Activities of the Particle Phenomenology Group

The Seminars and Journal Club sessions of previous years are listed below.

2013, 1st semester

Journal Club Sessions

02/05/2013, Eduardo Ponton: "Loop-induced Higgs couplings in WED"

References: 1301.7692, 1204.0008, 1006.5939

Abstract: The loop-induced couplings of the Higgs (that are relevant for its production via gluon fusion, or its discovery mode into two photons) can be sensitive to physics beyond the SM. In the context of warped extra-dimensional constructions, the Kaluza-Klein modes can give sizeable contributions to these processes that could be interesting in light of the most recent LHC results. The outcome is sensitive to whether the Higgs is delta-function localized on the IR brane, or whether it has a non-trivial bulk profile. Furthermore, in the case that the Higgs is exactly localized, incompatible results where found by two groups: http://arxiv.org/pdf/1006.5939.pdf and http://arxiv.org/pdf/1204.0008.pdf. More recently, http://arxiv.org/pdf/1301.7692.pdf investigated the origin of the difference.

The plan would be to discuss the latter paper, with the other two as background reading. The issue may or may not have been fully resolved...

03/14/2013, Ricardo Matheus: "Full-hierarchy Quiver Theories of Electroweak Symmetry Breaking and Fermion Masses"

References: 1210.5568

Abstract (of the paper): We consider quiver theories in four dimensions with a large ultra-violet cutoff. These theories require that an ordered set of vacuum expectation values for the link fields develops dynamically and can be obtained from the coarse deconstruction of extra-dimensional theories in an AdS background. These full-hierarchy quiver theories form a large class which include AdS$_5$ models as a limit, but which have a distinctive phenomenology. As an example, in this paper we show that fermions can be introduced in a way that can at the same time generate the fermion mass hierarchy and have flavor violation consistent with experimental bounds, when the mass scale of the color-octect gauge excitation is above $3 {\rm TeV}$. We also show that electroweak precision constraints are satisfied by this mass scale, without the need to extend the gauge sector to protect against custodial violation.

03/21/2013, Rogerio Rosenfeld: "The universal Higgs fit"

References: 1303.3570

Abstract (of the paper): We perform a state-of-the-art global fit to all Higgs data. We synthesise them into a 'universal' form, which allows to easily test any desired model. We apply the proposed methodology to extract from data the Higgs branching ratios, production cross sections, couplings and to analyse composite Higgs models, models with extra Higgs doublets, supersymmetry, extra particles in the loops, anomalous top couplings, invisible Higgs decay into Dark Matter. Best fit regions lie around the Standard Model predictions and are well approximated by our 'universal' fit. Latest data exclude the dilaton as an alternative to the Higgs, and disfavour fits with negative Yukawa couplings. We derive for the first time the SM Higgs boson mass from the measured rates, rather than from the peak positions, obtaining M_h = 124.2 pm 1.8 GeV.

03/28/2013, Adriano Natale: "The 125 GeV boson: A composite scalar?"

References: 1303.3248

Abstract (of the paper): Assuming that the 125 GeV particle observed at the LHC is a composite scalar and responsible for the electroweak gauge symmetry breaking, we consider the possibility that the bound state is generated by a non-Abelian gauge theory with dynamically generated gauge boson masses and a specific chiral symmetry breaking dynamics motivated by confinement. The scalar mass is computed with the use of the Bethe-Salpeter equation and its normalization condition as a function of the SU(N) group and the respective fermionic representation. If the fermions that form the composite state are in the fundamental representation of the SU(N) group, we can generate such light boson only for one specific number of fermions for each group. In the case of small groups, like SU(2) to SU(5), and two fermions in the adjoint representation we find that is quite improbable to generate such light composite scalar.

04/18/2013, Raphael Albuquerque: "Massive Nambu-Goldstone bosons"

References: 1303.1527 , also: 1204.1570

Abstract (of the paper): Nicolis and Piazza (1204.1570) have recently pointed out the existence of Nambu-Goldstone-like excitations in relativistic systems at finite density, whose gap is exactly determined by the chemical potential and the symmetry algebra. We show that the phenomenon is much more general than anticipated and demonstrate the presence of such modes in a number of systems from (anti)ferromagnets in magnetic field to superfluid phases of quantum chromodynamics. Furthermore, we prove a counting rule for these massive Nambu-Goldstone bosons and construct a low-energy effective Lagrangian that captures their dynamics.

04/25/2013, Gero von Gersdorff: "A Bayesian view of the Higgs sector with higher dimensional operators"

References: 1304.3369

Abstract (of the paper): We investigate the possibilities of New Physics affecting the Standard Model (SM) Higgs sector. An effective Lagrangian with dimension-six operators is used to capture the effect of New Physics. We carry out a global Bayesian inference analysis, considering the recent LHC data set including all available correlations, as well as results from Tevatron. Trilinear gauge boson couplings and electroweak precision observables are also taken into account. The case of weak bosons tensorial couplings is closely examined and NLO QCD corrections are taken into account in the deviations we predict. We consider two scenarios, one where the coefficients of all the dimension-six operators are essentially unconstrained, and one where a certain subset is loop suppressed. In both scenarios, we find that large deviations from some of the SM Higgs couplings can still be present, assuming New Physics arising at 3 TeV. In particular, we find that a significantly reduced coupling of the Higgs to the top quark is possible and slightly favored by searches on Higgs production in association with top quark pairs. The total width of the Higgs boson is only weakly constrained and can vary between 0.7 and 2.7 times the Standard Model value within 95% Bayesian credible interval (BCI). We also observe sizeable effects induced by New Physics contributions to tensorial couplings. In particular, the Higgs boson decay width into $Z\gamma$ can be enhanced by up to a factor 12 within 95% BCI.

05/02/2013, Eduardo Ponton: "Physical Naturalness and Dynamical Breaking of Classical Scale Invariance"

References: 1304.7006

Abstract (of the paper): The recent LHC data may suggest that the paradigm of naturalness, which has overwhelmingly guided model building beyond the standard model, should be revised. In a scheme-independent view of regularisation only physical mass scales give contributions of the order of that scale to the renormalised Higgs mass parameter. A self-consistent picture of electroweak symmetry breaking and renormalisation then emerges if, at the classical level, the space-time symmetry of the fundamental Lagrangian is maximally enhanced to the conformal group, which is ultimately broken down to the Lorentz group by quantum effects. That is, the Lagrangian is taken to be classically scale invariant, implying that any explicit mass scales are absent. As a concrete mechanism for generating the electroweak scale and providing dark matter candidates, we propose a model of a confining dark sector, dark technicolor, that communicates with the standard model only through the Higgs portal.

05/09/2013, Alberto Tonero: "Asymptotic safety of gravity and the Higgs boson mass" (joint JC @IFT)

Joint JC with USP group, hosted in IFT

References: 0912.0208

Abstract (of the paper): There are indications that gravity is asymptotically safe. The Standard Model (SM) plus gravity could be valid up to arbitrarily high energies. Supposing that this is indeed the case and assuming that there are no intermediate energy scales between the Fermi and Planck scales we address the question of whether the mass of the Higgs boson $m_H$ can be predicted. For a positive gravity induced anomalous dimension $A_\lambda>0$ the running of the quartic scalar self interaction $\lambda$ at scales beyond the Planck mass is determined by a fixed point at zero. This results in $m_H=m_{\rm min}=126$ GeV, with only a few GeV uncertainty. This prediction is independent of the details of the short distance running and holds for a wide class of extensions of the SM as well. For $A_\lambda <0$ one finds $m_H$ in the interval $m_{\rm min}< m_H < m_{\rm max}\simeq 174$ GeV, now sensitive to $A_\lambda$ and other properties of the short distance running. The case $A_\lambda>0$ is favored by explicit computations existing in the literature.

05/16/2013, Riccardo Sturani: "Classical Space-Times from the S Matrix"

References: 1304.7263

Abstract (of the paper): We show that classical space-times can be derived directly from the S-matrix for a theory of massive particles coupled to a massless spin two particle. As an explicit example we derive the Schwarzchild space-time as a series in $G_N$. At no point of the derivation is any use made of the Einstein-Hilbert action or the Einstein equations. The intermediate steps involve only on-shell S-matrix elements which are generated via BCFW recursion relations and unitarity sewing techniques. The notion of a space-time metric is only introduced at the end of the calculation where it is extracted by matching the potential determined by the S-matrix to the geodesic motion of a test particle. Other static space-times such as Kerr follow in a similar manner. Furthermore, given that the procedure is action independent and depends only upon the choice of the representation of the little group, solutions to Yang-Mills (YM) theory can be generated in the same fashion. Moreover, the squaring relation between the YM and gravity three point functions shows that the seeds that generate solutions in the two theories are algebraically related. From a technical standpoint our methodology can also be utilized to calculate quantities relevant for the binary inspiral problem more efficiently than the more traditional Feynman diagram approach.

05/23/2013, Leonardo de Lima: "Revisiting the Naturalness Problem -- Who is afraid of quadratic divergences? --" (joint JC @USP)

Joint JC with USP group, hosted in USP

References: 1201.0857, fnal: Conf-95-391-T.pdf

Abstract (of the paper): It is widely believed that quadratic divergences severely restrict natural constructions of particle physics models beyond the standard model (SM). Supersymmetry provides a beautiful solution, but the recent LHC experiments have excluded large parameter regions of supersymmetric extensions of the SM. It will now be important to reconsider whether we have been misinterpreting the quadratic divergences in field theories. In this paper, we revisit the problem from the viewpoint of the Wilsonian renormalization group and argue that quadratic divergences, which can always be absorbed into a position of the critical surface, should be simply subtracted in model constructions. Such a picture gives another justification to the argument that the scale invariance of the SM, except for the soft-breaking terms, is an alternative solution to the naturalness problem. It also largely broadens possibilities of model constructions beyond the SM since we just need to take care of logarithmic divergences, which cause mixings of various physical scales and runnings of couplings.

06/06/2013, Rogerio Rosenfeld: "How well do we need to measure the Higgs boson mass and self-coupling?"

References: 1305.6397

Much of the discussion regarding future measurements of the Higgs boson mass and self-coupling is focussed on how well various collider options can do. In this article we ask a physics-based question of how well do we need colliders to measure these quantities to have an impact on discovery of new physics or an impact in how we understand the role of the Higgs boson in nature. We address the question within the framework of the Standard Model and various beyond the Standard Model scenarios, including supersymmetry and theories of composite Higgs bosons. We conclude that the LHC's stated ability to measure the Higgs boson to better than 150 MeV will be as good as we will ever need to know the Higgs boson mass in the foreseeable future. On the other hand, we estimate that the self-coupling will likely need to be measured to better than 20 percent to see a deviation from the Standard Model expectation. This is a challenging target for future collider and upgrade scenarios.

06/13/2013, Ricardo Matheus: "A top condensate model with a Higgs doublet and a Higgs triplet" (joint JC @IFT)

Joint JC with USP group, hosted in IFT

References: 1304.7139

Abstract (of the paper): We reconsider top condensate models from the perspective that not only two quark composite fields can form but also four quark ones. We obtain a model which contains a Higgs doublet and a Higgs triplet, where one of the neutral components of the Higgs triplet identifies with the Higgs boson found at the LHC. We discuss some of the phenomenological consequences.

06/20/2013, Camila S. Machado: "Generalized Skyrmions in QCD and the Electroweak Sector"

References: 1209.6430

We discuss the stability and masses of topological solitons in QCD and strongly-interacting models of electroweak symmetry breaking with arbitrary combinations of two inequivalent Lagrangian terms of fourth order in the field spatial derivatives. We find stable solitons for only a restricted range of the ratio of these combinations, in agreement with previous results, and we calculate the corresponding soliton masses. In QCD, the experimental constraints on the fourth-order terms force the soliton to resemble the original Skyrmion solution. However, this is not necessarily the case in strongly-interacting models of electroweak symmetry breaking, in which a non-Skyrmion-like soliton is also possible. This possibility will be constrained by future LHC measurements and dark matter experiments. Current upper bounds on the electroweak soliton mass range between 18 and 59 TeV, which would be reduced to 4.6 to 8.1 TeV with the likely sensitivity of LHC data to the fourth-order electroweak Lagrangian parameters.

06/27/2013, André Lessa: "Electroweak Cogenesis" (joint JC @USP)

Joint JC with USP group, hosted in USP

References: 1306.4321

Abstract (of the paper): We propose a simple renormalizable model of baryogenesis and asymmetric dark matter generation at the electroweak phase transition. Our setup utilizes the two Higgs doublet model plus two complex gauge singlets, the lighter of which is stable dark matter. The dark matter is charged under a global symmetry that is broken in the early universe but restored during the electroweak phase transition. Because the ratio of baryon and dark matter asymmetries is controlled by model parameters, the dark matter need not be light. Thus, new force carriers are unnecessary and the symmetric dark matter abundance can be eliminated via Higgs portal interactions alone. Our model places a rough upper bound on the dark matter mass, and has implications for direct detection experiments and particle colliders.

Joint JCs

These are the dates and places for the Joint JCs for this semester:

(May 9th) Joint JC @IFT, 10:30 AM
(May 23th) Joint JC @USP, 5:30 PM
(June 13th) Joint JC @IFT, 10:30 AM
(June, 27th) Joint JC @USP, 5:30 PM

Seminars

04/19/2013, 4 pm, Zackaria Chacko: "The Dilaton, the Radion and Duality"

04/19/2013, 4 pm, room #3

References: 1304.1795, 1209.3259

Abstract: I consider scenarios where strong conformal dynamics constitutes the ultraviolet completion of the physics that drives electroweak symmetry breaking. I identify the circumstances under which the dilaton can remain light, and construct the effective theory of the light dilaton in this framework. The form of the dilaton couplings to Standard Model states is determined, and corrections from conformal symmetry violating effects are shown to be under good theoretical control in theories where the dilaton is light. Using the AdS/CFT correspondence, I show how the same results emerge from extra dimensional warped constructions, with the dilaton identified as the radion. I briefly consider the possibility that the recently discovered resonance at 125 GeV is a dilaton, rather than the Standard Model Higgs.

04/26/2013, 2 pm, Enrico Bertuzzo: "Composite Two Higgs doublet Models"

04/26/2013, 2 pm, room #3

References: 1206.2623

Abstract: I consider scenarios where strong conformal dynamics constitutes the ultraviolet completion of the physics that drives electroweak symmetry breaking. I identify the circumstances under which the dilaton can remain light, and construct the effective theory of the light dilaton in this framework. The form of the dilaton couplings to Standard Model states is determined, and corrections from conformal symmetry violating effects are shown to be under good theoretical control in theories where the dilaton is light. Using the AdS/CFT correspondence, I show how the same results emerge from extra dimensional warped constructions, with the dilaton identified as the radion. I briefly consider the possibility that the recently discovered resonance at 125 GeV is a dilaton, rather than the Standard Model Higgs.

04/30/2013, 2 pm, Maryam Tavakoli: "Constraints on dark matter properties from diffuse gamma-rays"

04/26/2013, 2 pm, room #2

05/29/2013, 4:30 pm, Aneesh Manohar: "Informal Discussion on Higher Dimensional Operators and Minimal Couplings"

05/29/2013, 4:30 pm

References: 1305.0017 , 1305.3927 , 1301.2588

2013, 2st semester

Journal Club Sessions

07/25/2013, Gero von Gersdorff: "Investigating the near-criticality of the Higgs boson"

References: 1307.3536

Abstract (of the paper): We extract from data the parameters of the Higgs potential and the top Yukawa coupling with full 2-loop NNLO precision, and we extrapolate the SM parameters up to large energies with full 3-loop NNLO RGE precision. Then we study the phase diagram of the Standard Model in terms of high-energy parameters, finding that the measured Higgs mass roughly corresponds to the minimum values of the Higgs quartic and top Yukawa and the maximum value of the gauge couplings allowed by vacuum metastability. We discuss various theoretical interpretations of the near-criticality of the Higgs mass.

08/01/2013, "Naturalness after LHC8"

References: 1307.7879

Abstract (of the paper): I review the status of naturalness of the weak scale after the results from the LHC operating at an energy of 8 TeV. Talk delivered at the 2013 Europhysics Conference on High Energy Physics (EPS), Stockholm, Sweden, 18-24 July 2013.

08/08/2013, Alberto Tonero: "Stringent limits on top-quark compositeness from top anti-top production at the Tevatron and the LHC"

References: 1307.5750

Abstract (of the paper): We show that in the minimal 3-3-1 model the flavor changing neutral currents (FCNCs) do not impose necessarily strong constraints on the mass of the $Z^\prime$ of the model if we also consider the neutral scalar contributions to such processes, like the neutral mesons mass difference and rare semileptonic decays. We first obtain numerical values for all the mixing matrices of the model i.e., the unitary matrices that rotate the left- and right-handed quarks in each charge sector which give the correct mass of all the quarks and the CKM mixing matrix. Then, we find that there is a range of parameters in which the neutral scalar contributions to these processes may interfere with those of the $Z^\prime$, implying this vector boson may be lighter than it has been thought.

08/15/2013, Bruno Lenzi: "Measurements of the Higgs boson properties with the ATLAS detector" (seminar)

References: 1307.1427, 1307.1432, ATLAS-CONF-2013-079, ATLAS-CONF-2012-160

About a year ago the ATLAS and CMS collaborations announced the observation of a new particle on the search for the Standard Model Higgs boson. The measurements of its properties such as rates in different decay channels, mass, couplings and spin using the 7 TeV and 8 TeV pp collision data collected in 2011 and 2012 with the ATLAS detector, are discussed.

08/22/2013, Vicente Pleitez: "FCNC in the minimal 3-3-1 model revisited"

References: 1305.1921

Abstract (of the paper): We show that in the minimal 3-3-1 model the flavor changing neutral currents (FCNCs) do not impose necessarily strong constraints on the mass of the $Z^\prime$ of the model if we also consider the neutral scalar contributions to such processes, like the neutral mesons mass difference and rare semileptonic decays. We first obtain numerical values for all the mixing matrices of the model i.e., the unitary matrices that rotate the left- and right-handed quarks in each charge sector which give the correct mass of all the quarks and the CKM mixing matrix. Then, we find that there is a range of parameters in which the neutral scalar contributions to these processes may interfere with those of the $Z^\prime$, implying this vector boson may be lighter than it has been thought.

09/12/2013, Ana C. B. Machado: "An 3HDM with S3 symmetry, dark matter and two inert doublets without FCNC"

References: 1206.6362

Abstract: We propose a new mechanism to suppress the flavor changing neutral currents in a three-Higgs doublet extension of the standard electroweak model. This mechanism has three ingredients: i) The three SU(2) Higgs scalar doublets transform as the reducible representation triplet of the discrete S3 symmetry that breaks to the irreducible representations, a doublet and a singlet; ii) an appropriate vacuum alignment and, iii) fermions transform as singlets of S3. The mass matrices in both, neutral and charged scalar sectors, have the same form and are diagonalized by the same unitary matrix. In some cases the latter matrix is of the tribimaximal type. However, the natural suppression of the flavor changing neutral processes does not depend on the form of this matrix. We also consider in these model that due to the new charged scalars there is an enhancement in the two-photon decay while the other channels have the same decay widths that the SM neutral Higgs. Finally, considering the introduction of right-handed neutrinos we can have good dark matter candidates.

10/02/2013, Camila S. Machado: "Twin Peak Higgs"

References: 1307.7146

Abstract (of the paper): A broad class of models in which electroweak symmetry breaking originates from dynamics in a singlet dark sector, and is transferred to the Standard Model via the Higgs portal, predicts in general strongly suppressed Higgs boson mixing with a singlet scalar. In this work we point out that at present this class of models allows for the second phenomenologically acceptable solution with almost maximal mixing between the Higgs and the scalar singlet. This scenario predicts an almost degenerate twin peak Higgs signal which is presently indistinguishable from a single peak, due to the limited LHC mass resolution. Because of that, the LHC experiments measure inclusive Higgs rates that all must exactly agree with Standard Model predictions due to sum rules. We show that if the dark sector and Standard Model communicate only via the singlet messenger scalar that mixes with the Higgs, the spin independent direct detection cross section of dark matter is suppressed by the scalar mass degeneracy, explaining its non-observation so far.

10/10/2013, Thiago Tomei Fernandez: "Identifying Hadronically Decaying Vector Bosons Merged into a Single Jet (and applications in BSM physics searches)"

References: CMS-PAS-JME-13-006, CMS-PAS-EXO-12-022, CMS-PAS-EXO-12-021

Abstract (of the paper): In the new energy regime of the LHC, it is becoming increasingly important for new physics searches to identify single jet objects which originate from and contain the decay products of a hadronically decaying massive W boson produced with high transverse momentum. A number of observables are explored for identifying these "W-jets". An algorithm is defined to identify jets originating from hadronically decaying W bosons for different signal scenarios. The efficiency for tagging W-jets is presented and comparisons are made between data and simulation. All the techniques discussed in identifying W-jets are applicable for other hadronic two-prong decays such as those from Z and Higgs bosons.

10/24/2013, Eduardo Ponton

References:

Abstract (of the paper):

10/31/2013, Michele Redi: "Axion-Higgs Unification" (seminar)

Abstract: I will discuss a unified framework for the Higgs boson and axion both arising from the spontaneous breaking of a non-abelian global symmetry G->H. The Goldstone symmetry of the Higgs is broken by the SM couplings while the axion shift symmetry is only broken by the QCD anomaly. Dark matter determines the decay constant of the Goldstone bosons f ~ 10^{11} GeV so that the electro-weak VEV is obtained by tuning. We present explicit examples in terms of SU(n) and SO(n) gauge theories when fermion masses are generated through bi-linear couplings of SM fermions as in technicolor. Axion-Higgs models can also be realized if SM fields couple linearly as in modern composite Higgs constructions, most simply within the pattern SO(6)/SO(5). We also show that with a large compositeness scale, a 125 GeV Higgs mass may follow from the Goldstone nature of the Higgs.

11/07/2013, First Particle Physics Phenomenology and Theory Workshop

This is the first workshop with the high energy groups in USP and IFT/ICTP-SAIFR.
The main idea of the workshop is to give the groups in each institute an opportunity to present to each other their current work and future plans. It is also a good opportunity for the newcomers to present their interests and recent work. The presentations are very informal and short (~15-20min) and cover current research topics, leaving plenty of time for discussions.

DETAILS AND PROGRAMME HERE

11/14/2013, Nicolás Bernal: "Dark matter production from Goldstone boson interactions and implications for direct searches and dark radiation"

References: 1310.6256

Abstract: The stability of the dark matter particle could be attributed to the remnant Z2 symmetry that arises from the spontaneous breaking of a global U(1) symmetry. This plausible scenario contains a Goldstone boson which, as recently shown by Weinberg, is a strong candidate for dark radiation. We show in this paper that this Goldstone boson, together with the CP-even scalar associated to the spontaneous breaking of the global U(1) symmetry, plays a central role in the dark matter production. Besides, the mixing of the CP-even scalar with the Standard Model Higgs boson leads to novel Higgs decay channels and to interactions with nucleons, thus opening the possibility of probing this scenario at the LHC and in direct dark matter search experiments. We carefully analyze the latter possibility and we show that there are good prospects to observe a signal at the future experiments LUX and XENON1T provided the dark matter particle was produced thermally and has a mass larger than ~25 GeV.

11/21/2013, Oscar Eboli: "Electroweak Effective Operators and Higgs Physics" (joint JC @USP)

Joint JC with USP group, hosted in USP

References: 1311.3107

Abstract (of the paper): We derive bounds from oblique parameters on the dimension-6 operators of an effective field theory of electroweak gauge bosons and the Higgs doublet. The loop- induced contributions to the S, T, and U oblique parameters are sensitive to these contributions and we pay particular attention to the role of renormalization when computing loop corrections in the effective theory. Limits on the coefficients of the effective theory from loop contributions to oblique parameters yield complementary information to direct Higgs production measurements.

11/28/2013, Sylvain Fichet: "Anomalous gauge couplings from composite Higgs and warped extra dimensions" (seminar)

Abstract: We examine trilinear and quartic anomalous gauge couplings (AGCs) generated in composite Higgs models and models with warped extra dimensions. We first  revisit the $SU(2)_L\times U(1)_Y$ effective Lagrangian and derive the charged and two-photon neutral AGCs. We derive the general perturbative contributions to the pure field-strength operators from spin $0$, $\frac{1}{2}$, $1$ resonances by means of the heat kernel method. In the composite Higgs framework, we derive the pattern of expected deviations from typical $SO(N)$ embeddings of the light composite top partner. We then study a generic warped extra dimension framework with $AdS_5$ background, recasting in few parameters the features of models relevant for AGCs. We also present a detailed study of the latest bounds from electroweak and Higgs precision observables, with and without brane kinetic terms. For vanishing brane kinetic terms, we find that the $S$ and $T$ parameters exclude KK gauge modes of the RS custodial [non-custodial] scenario  below  $7.7$ [$14.7$] TeV,  for a brane Higgs  and below $6.6$ [$8.1$] TeV for a Pseudo Nambu-Goldstone Higgs, at $95\%$ CL. These constraints can be relaxed in presence of brane kinetic terms. The leading AGCs are probing the KK gravitons and the KK modes of bulk gauge fields in parts of the parameter space. In these scenarios, the future ATLAS Forward Proton detector could   be sensitive to the effect of   KK gravitons in the multi-TeV mass range. 

12/05/2013, Gero von Gersdorff: "An Equivalent Gauge and the Equivalence Theorem" (joint JC @IFT)

Joint JC with USP group, hosted in IFT

References: 1309.6055

Abstract (of the paper): I describe a novel covariant formulation of massive gauge theories in which the longitudinal polarization vectors do not grow with the energy. Therefore in the present formalism, differently from the ordinary one, the energy and coupling power-counting is completely transparent at the level of individual Feynman diagrams, with obvious advantages both at the conceptual and practical level. Since power-counting is transparent, the high-energy limit of the amplitudes involving longitudinal particles is immediately taken, and the Equivalence Theorem is easily demonstrated at all orders in perturbation theory. Since the formalism makes the Equivalence Theorem self-evident, and because it is based on a suitable choice of the gauge, we can call it an "Equivalent Gauge".

Joint JCs

These are the dates and places for the Joint JCs for this semester:

(October 7th) First Particle Physics Phenomenology and Theory Workshop, details and programme
(November 21th) Joint JC @USP, 5:30 PM
(December 5th) Joint JC @IFT, 2:00 PM


Seminars

08/15/2013, 2:30 pm, Bruno Lenzi (ATLAS): "Measurements of the Higgs boson properties with the ATLAS detector"

08/15/2013, 2:30 pm, room #3

References: 1307.1427, 1307.1432, ATLAS-CONF-2013-079, ATLAS-CONF-2012-160

About a year ago the ATLAS and CMS collaborations announced the observation of a new particle on the search for the Standard Model Higgs boson. The measurements of its properties such as rates in different decay channels, mass, couplings and spin using the 7 TeV and 8 TeV pp collision data collected in 2011 and 2012 with the ATLAS detector, are discussed.

09/26/2013, 2 pm, Jorge Morfin (Fermilab): "The Intensity Frontier Experimental Program at Fermilab"

09/26/2013, 2 pm, auditorium

The Intensity Frontier program at Fermilab covers muon experiments like Mu2e and g-2 and kaon experiments like ORKA. However, the emphasis is on neutrino experiments that include MINERvA, MINOS+, NOvA, MicroBooNE and LBNE. Recently the MINERvA experiment published results on charged-current quasi elastic scattering that may shed light on the role of correlated nucleon pairs in neutrino-nucleus interactions. A description of the entire Intensity Frontier program will be presented with emphasis on neutrinos.

09/27/2013, 2 pm, Laura López (Vrije Universiteit Brussel): "Significant gamma ray signal from dark matter: Scalar versus Majorana"

09/27/2013, 2 pm, auditorium

There has been interest recently on particle physics models that may give rise to sharp gamma ray spectral features from dark matter annihilation. Because dark matter is supposed to be electrically neutral, it is challenging to build weakly interacting massive particle models that may accommodate both a large cross section into gamma rays at, say, the Galactic center, and the right dark matter abundance. In my talk, I will discuss the gamma ray signatures of real scalar and Majorana dark matter annihilating into lepton-antilepton pairs. In both cases, the two-body final-state annihilation channel will turn out to be velocity suppressed in the chiral limit. This allow for large contributions to the annihilation cross-section from virtual internal bremsstrahlung emission of a gamma ray. I will show that the virtual internal bremsstrahlung signal may be enhanced by a factor of (up to) two orders of magnitude in the case of scalar dark matter.

09/30/2013, 2 pm, Claudia Frugiuele (Fermilab): "Mixing stops at the LHC"

09/30/2013, 2 pm, room 3

I will discuss the phenomenology of a light stop NLSP in the presence of large mixing with either the first or the second generation.  R-symmetric models provide a prime setting for this scenario, but this also applies to the MSSM when a significant amount of mixing can be accommodated.  In our framework the dominant stop decay is through the flavor violating mode into a light jet and the LSP in an extended region of parameter space.  There are currently no public limits from ATLAS and CMS in this region.  However, I will show that shape-based hadronic SUSY searches for this topology have potential sensitivity and can set strong exclusion limits on light stops.

10/31/2013, 2 pm, Michele Redi (INFN and Galileo Galilei Institute): "Axion-Higgs Unification"

10/31/2013, 2 pm, room 3

I will discuss a unified framework for the Higgs boson and axion both arising from the spontaneous breaking of a non-abelian global symmetry G->H. The Goldstone symmetry of the Higgs is broken by the SM couplings while the axion shift symmetry is only broken by the QCD anomaly. Dark matter determines the decay constant of the Goldstone bosons f ~ 10^{11} GeV so that the electro-weak VEV is obtained by tuning. We present explicit examples in terms of SU(n) and SO(n) gauge theories when fermion masses are generated through bi-linear couplings of SM fermions as in technicolor. Axion-Higgs models can also be realized if SM fields couple linearly as in modern composite Higgs constructions, most simply within the pattern SO(6)/SO(5). We also show that with a large compositeness scale, a 125 GeV Higgs mass may follow from the Goldstone nature of the Higgs.

11/28/2013, 2 pm, Sylvain Fichet (International Institute of Physics - UFRN): "Anomalous gauge couplings from composite Higgs and warped extra dimensions"

11/28/2013, 2 pm, room 3

We examine trilinear and quartic anomalous gauge couplings (AGCs) generated in composite Higgs models and models with warped extra dimensions. We first  revisit the $SU(2)_L\times U(1)_Y$ effective Lagrangian and derive the charged and two-photon neutral AGCs. We derive the general perturbative contributions to the pure field-strength operators from spin $0$, $\frac{1}{2}$, $1$ resonances by means of the heat kernel method. In the composite Higgs framework, we derive the pattern of expected deviations from typical $SO(N)$ embeddings of the light composite top partner. We then study a generic warped extra dimension framework with $AdS_5$ background, recasting in few parameters the features of models relevant for AGCs. We also present a detailed study of the latest bounds from electroweak and Higgs precision observables, with and without brane kinetic terms. For vanishing brane kinetic terms, we find that the $S$ and $T$ parameters exclude KK gauge modes of the RS custodial [non-custodial] scenario  below  $7.7$ [$14.7$] TeV,  for a brane Higgs  and below $6.6$ [$8.1$] TeV for a Pseudo Nambu-Goldstone Higgs, at $95\%$ CL. These constraints can be relaxed in presence of brane kinetic terms. The leading AGCs are probing the KK gravitons and the KK modes of bulk gauge fields in parts of the parameter space. In these scenarios, the future ATLAS Forward Proton detector could   be sensitive to the effect of   KK gravitons in the multi-TeV mass range. 

2014, 1st semester

Journal Club Sessions

02/04/2014 (Tuesday, 2:00pm), Gero von Gersdorff: "Higgs mass from compositeness at a multi-TeV scale"

References: 1311.5928

Abstract (of the paper): Within composite Higgs models based on the top seesaw mechanism, we show that the Higgs field can arise as the pseudo Nambu-Goldstone boson of the broken U(3)_L chiral symmetry associated with a vector-like quark and the t-b doublet. As a result, the lightest CP-even neutral state of the composite scalar sector is lighter than the top quark, and can be identified as the newly discovered Higgs boson. Constraints on weak isospin violation push the chiral symmetry breaking scale above a few TeV, implying that other composite scalars are probably too heavy to be probed at the LHC, but may be within reach at a future hadron collider with center-of-mass energy of about 100 TeV.

02/13/2014, Leonardo de Lima: "Deconstructing Dimensions and Massive Gravity"

References: 1308.4136

Abstract (of the paper): We show that the ghost-free models of massive gravity and their multi-graviton extensions follow from considering higher dimensional General Relativity in Einstein-Cartan form on a discrete extra dimension, according to the Dimensional Deconstruction paradigm. We show that Dimensional Deconstruction is equivalent to a truncation of the Kaluza-Klein tower at the nonlinear level. Higher dimensional gravity is not recovered from a lower dimensional multi-graviton theory in the limit of a continuous extra dimension (infinite Kaluza-Klein tower) due to the appearance of a low strong coupling scale that depends on IR physics. This strong coupling scale, which is associated with the mass of the lowest Kaluza-Klein mode, controls the onset of the Vainshtein mechanism and is crucial to the theoretical and observational viability of the truncated theory.

02/27/2014, Yuber F Perez G: "Basis invariant measure of CP-violation and renormalization" (joint JC @USP)

Joint JC with USP group, hosted in USP

References: 1309.1385

Abstract (of the paper): We analyze, in the context of a simple toy model, for which renormalization schemes the CP-properties of bare Lagrangian and its finite part coincide. We show that this is the case for the minimal subtraction and on-shell schemes. The CP-properties of the theory can then be characterized by CP-odd basis invariants expressed in terms of renormalized masses and couplings.

03/06/2014, Nicolás Bernal: "The SIMP Miracle"

References: 1402.5143

Abstract (of the paper): We present a new paradigm for achieving thermal relic dark matter. The mechanism arises when a nearly secluded dark sector is thermalized with the Standard Model after reheating. The freezeout process is a number-changing 3->2 annihilation of strongly-interacting-massive-particles (SIMPs) in the dark sector, and points to sub-GeV dark matter. The couplings to the visible sector, necessary for maintaining thermal equilibrium with the Standard Model, imply measurable signals that will allow coverage of a significant part of the parameter space with future indirect- and direct-detection experiments and via direct production of dark matter at colliders. Moreover, 3->2 annihilations typically predict sizable 2->2 self-interactions which naturally address the `core vs. cusp' and `too-big-to-fail' small structure problems.

03/13/2014, Ricardo Matheus: "Bounding the top Yukawa with Higgs-associated single-top production" (joint JC @IFT)

Joint JC with USP group, hosted in IFT

References: 1402.0445

Abstract (of the paper): After the discovery of the 125 GeV scalar boson with gauge properties similar to the Standard Model Higgs, the search for beyond the SM interactions will focus on studying the discovered particles' coupling properties more precisely and shedding light on the relation of fermion masses with the electroweak vacuum. The large mass of the top quark and the SM-predicted order one top Yukawa coupling is a natural candidate for BSM physics, though experimentally challenging to constrain. In this paper, we argue that investigating angular correlations in  pptH j  production provides an excellent handle to constrain the top Yukawa coupling  y_t  via direct measurements, even when we focus on rare exclusive final states. We perform a hadron-level analysis and show that we may expect to constrain  y_t \geq 0.5 y^{SM}_t  at 95%-99% confidence level at the high luminosity LHC using semi-leptonic top decays and  H γ γ  alone, by employing a two-channel measurement approach.

03/20/2014, Rogerio Rosenfeld: "Some implications of BICEP2 results"

03/27/2014, Gabriela Lima Lichtenstein: "Effective field theory and keV lines from dark matter" (joint JC @USP)

Joint JC with USP group, hosted in USP

References: 1403.1240

Abstract (of the paper): We survey operators that can lead to a keV photon line from dark matter decay or annihilation. We are motivated in part by recent claims of an unexplained 3.5 keV line in galaxy clusters and in Andromeda, but our results could apply to any hypothetical line observed in this energy range. We find that given the amount of flux that is observable, explanations in terms of decay are more plausible than annihilation, at least if the annihilation is directly to Standard Model states rather than intermediate particles. The decay case can be explained by a scalar or pseudoscalar field coupling to photons suppressed by a scale not far below the reduced Planck mass, which can be taken as a tantalizing hint of high-scale physics. The scalar case is particularly interesting from the effective field theory viewpoint, and we discuss it at some length. Because of a quartically divergent mass correction, naturalness strongly suggests the theory should be cut off at or below the 1000 TeV scale. The most plausible such natural UV completion would involve supersymmetry. These bottom-up arguments reproduce expectations from top-down considerations of the physics of moduli. A keV line could also arise from the decay of a sterile neutrino, in which case a renormalizable UV completion exists and no direct inference about high-scale physics is possible.

04/03/2014, Saeed Mirshekari: "Spontaneous Scalarization in Scalar-Tensor Theories of Gravity"

References: 1212.5053

04/10/2014, Horatiu Nastase: "Conformal inflation from the Higgs" (joint JC @IFT)

Joint JC with USP group, hosted in IFT

Abstract: Conformal inflation is a model with local Weyl invariance, a dynamical Planck scale and an SO(1,1) invariance at high energies. A related cyclic Higgs model obtains the Higgs at low energies and cyclic cosmology at high energies, using also a local Weyl invariant model. We combine the two models, obtaining conformal inflation at high energies and Higgs at low energies. The general set-up is an exponentially-corrected plateau giving a generalized Starobinsky model, with an infinite series of R^p corrections instead of just the first term, leading to a general tensor to scalar ratio r that can be made compatible with BICEP2, unlike the simple Starobinsky model. Introducing a scalar-gravity coupling different from the conformal value leads nevertheless to a strong attractor behaviour towards the Starobinsky line.

04/24/2014, Chee Sheng Fong: "7 keV Scalar Dark Matter and the Anomalous Galactic X-ray Spectrum" (joint JC @USP)

Joint JC with USP group, hosted in USP

References: 1404.2220

Abstract (of the paper): We present a simple model for a 7 keV scalar dark matter particle which also explains the recently reported anomalous peak in the galactic X-ray spectrum at 3.55 keV in terms of its two photon decay. The model is arguably the simplest extension of the Standard Model, with the addition of a real scalar gauge singlet field subject to a reflection symmetry. This symmetry breaks spontaneously at an energy scale of a few MeV which triggers the decay of the dark matter particle into two photons. In this framework, the Higgs boson of the Standard Model is also the source of dark matter in the Universe. The model fits the relic dark matter abundance and the partial lifetime for two photon decay, while being consistent with constraints from domain wall formation and dark matter self-interactions. We show that all these features of the model are preserved in its natural embedding into a simple dark  U (1)  gauge theory with a Higgs mechanism. The properties of the dark photon get determined in such a scenario. High precision cosmological measurements can potentially test these models, as there are residual effects from domain wall formation and non-negligible self-interactions of dark matter.

05/08/2014, Alberto Tonero: "Dipole-induced anomalous top quark couplings at the LHC"

References: 1404.2581

Abstract (of the paper): We consider direct bounds on the coefficients of higher dimensional top quark dipole operators from their contributions to anomalous top couplings that affect some related processes at the LHC. Several observables are studied. In particular, we incorporate for the first time in this type of analysis the recently measured associated ttbarV production, which is currently the only measured direct observable sensitive to the dipole operator involving the hypercharge field. We perform a Bayesian analysis to derive the 1(2)σ confidence level (CL) intervals on these coefficients.

05/14/2014, Ana Machado: "The Quest for an Intermediate-Scale Accidental Axion and Further ALPs" (joint JC @IFT)

Joint JC with USP group, hosted in IFT

Abstract (of the paper): The recent detection of the cosmic microwave background polarimeter experiment BICEP2 of tensor fluctuations in the B-mode power spectrum basically excludes all plausible axion models where its decay constant is above 10^13 GeV. Moreover, there are strong theoretical, astrophysical, and cosmological motivations for models involving, in addition to the axion, also axion-like particles (ALPs), with decay constants in the intermediate scale range, between 10^9 GeV and 10^13 GeV. Here, we present a general analysis of models with an axion and further ALPs and derive bounds on the relative size of the axion and ALP photon (and electron) coupling. We discuss what we can learn from measurements of the axion and ALP photon couplings about the fundamental parameters of the underlying ultraviolet completion of the theory. For the latter we consider extensions of the Standard Model in which the axion and the ALP(s) appear as pseudo Nambu-Goldstone bosons from the breaking of global chiral U(1) (Peccei-Quinn (PQ)) symmetries, occuring accidentally as low energy remnants from exact discrete symmetries. In such models, the axion and the further ALP are protected from disastrous explicit symmetry breaking effects due to Planck-scale suppressed operators. The scenarios considered exploit heavy right handed neutrinos getting their mass via PQ symmetry breaking and thus explain the small mass of the active neutrinos via a seesaw relation between the electroweak and an intermediate PQ symmetry breaking scale. We show some models that can accommodate simultaneously an axion dark matter candidate, an ALP explaining the anomalous transparency of the universe for γ-rays, and an ALP explaining the recently reported 3.55 keV gamma line from galaxies and clusters of galaxies, if the respective decay constants are of intermediate scale.

05/28/2014, Renata Funchal: "Anarchy and Hierarchy" (joint JC @USP)

Joint JC with USP group, hosted in USP

References: hep-ph/0009174

Abstract (of the paper): We advocate a new approach to study models of fermion masses and mixings, namely anarchy proposed in hep-ph/9911341. In this approach, we scan the O(1) coefficients randomly. We argue that this is the correct approach when the fundamental theory is sufficiently complicated. Assuming there is no physical distinction among three generations of neutrinos, the probability distributions in MNS mixing angles can be predicted independent of the choice of the measure. This is because the mixing angles are distributed according to the Haar measure of the Lie groups whose elements diagonalize the mass matrices. The near-maximal mixings, as observed in the atmospheric neutrino data and as required in the LMA solution to the solar neutrino problem, are highly probable. A small hierarchy between the Delta m^2 for the atmospheric and the solar neutrinos is obtained very easily; the complex seesaw case gives a hierarchy of a factor of 20 as the most probable one, even though this conclusion is more measure-dependent. U_{e3} has to be just below the current limit from the CHOOZ experiment. The CP-violating parameter sin delta is preferred to be maximal. We present a simple SU(5)-like extension of anarchy to the charged-lepton and quark sectors which works well phenomenologically.

Joint JCs

These are the dates and places for the Joint JCs for this semester:

(February 27th) Joint JC @USP, 5:30 PM
(March 13th) Joint JC @IFT, 2:00 PM
(March 27th) Joint JC @USP, 5:30 PM
(April 10th) Joint JC @IFT, 2:00 PM
(April 24th) Joint JC @USP, 5:30 PM
(May 15th) Joint JC @IFT, 2:00 PM
(May 29th) Joint JC @USP, 5:30 PM
More TBA (World cup complications)

Seminars

03/12/2014, 11:00 am, Antonio Delgado (University of Notre Dame): "Phenomenology of the LSSM"

03/12/2014, 11:00 am, Auditorium

I will present a top-bottom approach to "natural susy" based on two sources of supersymmetry breaking. I will describe the model as well as its phenomenology at the LHC.

03/26/2014, 11:00 am, Diogo Boito (Technische Universität München): "Issues in alpha_s determinations from tau decays"

03/26/2014, 11:00 am, Room 3, 3rd floor

I will present a discussion of recent developments in the QCD description of hadronic tau decays with emphasis in the perturbative contribution. The perturbative series is the main ingredient in the extraction of the strong coupling (alpha_s) from these decays. The ambiguity due to the different prescriptions regarding the renormalization group improvement of the series will be studied under different assumptions for the large-order corrections. Our results show that some of the moments of the hadronic spectral functions employed in alpha_s determinations have bad perturbative behaviour and should be avoided. The goal of our study is to develop the optimal theoretical framework for alpha_s extractions from the 2014 update of the ALEPH data.

2014, 2nd semester

Journal Club Sessions

07/24/2014, Camila Machado: "Electroweak and Conformal Symmetry Breaking by a Strongly Coupled Hidden Sector"

References: 1310.4423

Abstract (of the paper): The LHC and other experiments show so far no sign of new physics and long-held beliefs about naturalness should be critically reexamined. We discuss therefore in this paper a model with a combined breaking of conformal and electroweak symmetry by a strongly coupled hidden sector. Even though the conformal symmetry is anomalous, this may still provide an explanation of the smallness of electroweak scale compared to the Planck scale. Specifically we start from a classically conformal model, in which a strongly coupled hidden sector undergoes spontaneous chiral symmetry breaking. A coupling via a real scalar field transmits the breaking scale to the Standard Model Higgs and triggers electroweak symmetry breaking. The model contains dark matter candidates in the form of dark pions, whose stability is being guaranteed by the flavor symmetry of hidden quark sector. We study its relic abundance and direct detection prospects with the Nambu-Jona-Lasinio method and discuss the phase transition in the dark sector as well as in the electroweak sector..

08/07/2014, Sylvain Fichet: "Detecting extradimensions with light-by-light scattering at the LHC"

08/28/2014, Arhrib Abdesslam: "Phenomenology of Inert Higgs Models" (joint JC @IFT)

Joint JC with USP group, hosted in IFT

References:

09/04/2014, Leonardo de Lima: "Effective Theories and Measurements at Colliders"

References: 1408.5147

Abstract (of the paper): If the LHC run 2 will not provide conclusive hints for new resonant Physics beyond the Standard Model, dedicated and consistent search strategies at high momentum transfers will become the focus of searches for anticipated deviations from the Standard Model expectation. We discuss the phenomenological importance of QCD and electroweak corrections in bounding higher dimensional operators when analysing energy-dependent differential distributions. In particular, we study the impact of RGE-induced operator running and mixing effects on measurements performed in the context of an Effective Field Theory extension of the SM. Furthermore we outline a general analysis strategy which allows a RGE-improved formulation of constraints free of theoretical shortcomings that can arise when differential distributions start to probe the new interaction scale. We compare the numerical importance of such a programme against the standard analysis approach which is widely pursued at present.

09/11/2014, Alejandro Ibarra: "Signatures of the Inert Doublet Dark Matter Model" (joint JC @IFT)

Joint JC with USP group, hosted in IFT

References:

09/25/2014, Nicolás Bernal: "Particle-antiparticle asymmetries from annihilations" (joint JC @USP)

References: 1407.4566

Abstract (of the paper): An extensively studied mechanism to create particle-antiparticle asymmetries is the out-of-equilibrium and CP violating decay of a heavy particle. Here we instead examine how asymmetries can arise purely from 2 <-> 2 annihilations rather than from the usual 1 <-> 2 decays and inverse decays. We review the general conditions on the reaction rates that arise from S-matrix unitarity and CPT invariance, and show how these are implemented in the context of a simple toy model. We formulate the Boltzmann equations for this model, and present an example solution.

10/09/2014, Maria Eugenia: "Identifying boosted new physics with non-isolated leptons" (joint JC @USP)

References: 1410.0362

Abstract (of the paper): We demonstrate the utility of leptons which fail standard isolation criteria in searches for new physics at the LHC. Such leptons can arise in any event containing a highly boosted particle which decays to both leptons and quarks. We begin by considering multiple extensions to the Standard Model which primarily lead to events with non-isolated leptons and are therefore missed by current search strategies. We emphasize the failure of standard isolation variables to adequately discriminate between signal and SM background for any value of the isolation cuts. We then introduce a new approach which makes use of jet substructure techniques to distinguish a broad range of signals from QCD events. We proceed with a simulated, proof-of-principle search for R-parity violating supersymmetry to demonstrate both the experimental reach possible with the use of non-isolated leptons and the utility of new substructure variables over existing techniques.

10/16/2014, Christophe Royon: "Forward Physics at the LHC with tagged protons"

Abstract: We will describe briefly some of the physics topics that can be studied at the LHC using tagged protons, namely QCD and the structure of the pomeron in terms of quarks and gluons, as well as the search for extra-dimensions in the universe via anomalous couplings between photon, W and Z. We will finish the seminar by decribing briefly the new detectors that will be installed to achieve these measurements.

10/23/2014, Gero von Gersdorff: "Holomorphy in the Standard Model Effective Field Theory" (joint JC @IFT)

References: 1409.0868

Abstract (of the paper): The anomalous dimensions of dimension-six operators in the Standard Model Effective Field Theory (SMEFT) respect holomorphy to a large extent. The holomorphy conditions are reminiscent of supersymmetry, even though the SMEFT is not a supersymmetric theory.

10/16/2014, Eduardo Pontón: "Running Electroweak Couplings as a Probe of New Physics"

References: 1410.6810

Abstract (of the paper): The energy dependence of the electroweak gauge couplings has not been measured above the weak scale. We propose that percent-level measurements of the energy dependence of a1,2 can be performed now at the LHC and at future higher energy hadron colliders. These measurements can be used to set limits on new particles with electroweak quantum numbers without relying on any assumptions about their decay properties. The shape of the high invariant mass spectrum of Drell-Yan, pp?Z*/?*?l+l-, constrains a1,2(Q), and the shape of the high transverse mass distribution of pp?W*?l? constrains a2(Q). We use existing data to perform the first fits to a1,2 above the weak scale. Percent-level measurements are possible because of high precision in theoretical predictions and existing experimental measurements. We show that the LHC already has the reach to improve upon electroweak precision tests for new particles that dominantly couple through their electroweak charges. The 14 TeV LHC is sensitive to the predicted Standard Model (SM) running of a2, and can show that a2 decreases with energy at 2-3s significance. A future 100 TeV proton-proton collider will have significant reach to measure running weak couplings, with sensitivity to the SM running of a2 at 4-5s and sensitivity to winos with masses up to ~ 1.3 TeV at 2s.

11/06/2014, Oscar Éboli: "Vetoed jet clustering: The mass-jump algorithm" (joint JC @USP)

References: 1410.4637

Abstract (of the paper): An extensively studied mechanism to create particle-antiparticle asymmetries is the out-of-equilibrium and CP violating decay of a heavy particle. Here we instead examine how asymmetries can arise purely from 2 <-> 2 annihilations rather than from the usual 1 <-> 2 decays and inverse decays. We review the general conditions on the reaction rates that arise from S-matrix unitarity and CPT invariance, and show how these are implemented in the context of a simple toy model. We formulate the Boltzmann equations for this model, and present an example solution.

Joint JCs

These are the dates and places for the Joint JCs for this semester:

(August 28th) Joint JC @IFT, 2:00 PM
(September 11th) Joint JC @IFT, 2:00 PM
(September 25th) Joint JC @USP, 5:30 PM
(October 9th) Joint JC @USP, 5:30 PM
(October 23th) Joint JC @IFT, 2:00 PM
(November 6th) Joint JC @USP, 5:30 PM

Seminars

08/07/2014, 2:00 pm, Sylvain Fichet (International Institute of Physics, UFRN): "Detecting extradimensions with light-by-light scattering at the LHC"

08/07/2014, 2:00 pm, Room 3, 3rd floor

References: 1304.3369, 1307.0544, 1311.6815, 1312.5153

09/11/2014, 2:00 pm, Alejandro Ibarra (Technische Universität München): "Signatures of the Inert Doublet Dark Matter Model"

09/11/2014, 2:00 pm, Room 3, 3rd floor

References:

10/16/2014, 2:00 pm, Christophe Royon (IRFU, Saclay / Atlas Collaboration): "Forward Physics at the LHC with tagged protons"

10/16/2014, 2:00 pm, Room 3, 3rd floor

Abstract: We will describe briefly some of the physics topics that can be studied at the LHC using tagged protons, namely QCD and the structure of the pomeron in terms of quarks and gluons, as well as the search for extra-dimensions in the universe via anomalous couplings between photon, W and Z. We will finish the seminar by decribing briefly the new detectors that will be installed to achieve these measurements.

2015, 1st semester

Journal Club Sessions

1/29/2015, Chee Sheng Fong: "Dynamical flavor origin of ZN symmetries" (joint JC @IFT)

References: 1412.5600

Abstract (of the paper): Discrete Abelian symmetries (ZN) are a common "artifact" of beyond the standard model physics models. They provide different avenues for constructing consistent scenarios for lepton and quark mixing patterns, radiative neutrino mass generation as well as dark matter stabilization. We argue that these symmetries can arise from the spontaneous breaking of the Abelian U(1) factors contained in the global flavor symmetry transformations of the gauge invariant kinetic Lagrangian. This will be the case provided the ultra-violet completion responsible for the Yukawa structure involves scalar fields carrying non-trivial U(1) charges. Guided by minimality criteria, we demonstrate the viability of this approach with two examples: first, we derive the "scotogenic" model Lagrangian, and second, we construct a setup where the spontaneous symmetry breaking pattern leads to a Z3 symmetry which enables dark matter stability as well as neutrino mass generation at the 2-loop order. This generic approach can be used to derive many other models, with residual ZN or ZN1 x ... x ZNk symmetries, establishing an intriguing link between flavor symmetries, neutrino masses and dark matter.

2/12/2015, André Lessa: "Warm Dark Matter in Two Higgs Doublet Models" (joint JC @USP)

References: 1412.7745

Abstract (of the paper): We show that a neutral scalar field, \sigma, of two Higgs doublet extensions of the Standard Model incorporating the seesaw mechanism for neutrino masses can be identified as a consistent {\it warm} dark matter candidate with a mass of order keV. The relic density of σ is correctly reproduced by virtue of the late decay of a right-handed neutrino N participating in the seesaw mechanism. Constraints from cosmology determine the mass and lifetime of N to be M_N = 25 GeV - 20 TeV and \tau_N = (10^{-4} - 1) sec. These models can also explain the 3.5 keV X-ray anomaly in the extra-galactic spectrum that has been recently reported in terms of the decay \sigma \to \gamma \gamma. Future tests of these models at colliders and in astrophysical settings are outlined.

2/26/2015, Ricardo Matheus: "Model-independent precision constraints on dimension-6 operators"

References: 1411.0669

Abstract (of the paper): We discuss electroweak precision constraints on dimension-6 operators in the effective theory beyond the standard model. We identify the combinations of these operators that are constrained by the pole observables (the W and Z masses and on-shell decays) and by the W boson pair production. To this end, we define a set of effective couplings of W and Z bosons to fermions and to itself, which capture the effects of new physics corrections. This formalism clarifies which operators are constrained by which observable, independently of the adopted basis of operators. We obtain numerical constraints on the coefficients of dimension-6 operator in a form that can be easily adapted to any particular basis of operators, or any particular model with new heavy particles.

3/5/2015, Maury Goodman: "Status of the Experiment at the Long-Baseline Neutrino Facility ELBNF" (joint JC @IFT)

ELBNF is part of an ambitious worldwide program to understand the neutrino. It will consist of a 40-kt modular liquid argon TPC located deep underground. The principal goals are to carry out a comprehensive investigation of neutrino oscillations to test CP violation in the lepton sector, to determine the ordering of the neutrino masses, and to test the three neutrino paradigm; to perform a broad set of neutrino scattering measurements with the near detector; and to exploit the large, high-resolution, underground far detector for non-accelerator physics topics, including atmospheric neutrino measurements, searches for nucleon decay, and measurement of astrophysical neutrinos, especially those from a core-collapse supernova.

3/12/2015, Alberto Tonero: "Gluon-initiated associated production boosts Higgs physics"

References: 1310.4828

Abstract (of the paper): Analyses of boosted Higgs bosons from associated production comprise some of the main search channels for the Higgs boson at the LHC. The gluon-initiated gg→hZ subprocess has largely been ignored in phenomenological analyses of boosted associated production although this contribution is sizable as the pT spectrum for this process is maximised in the boosted regime due to the top quark loop threshold. In this paper, we discuss this contribution to boosted pp→hZ analyses in detail. We find there are previously overlooked modifications of Standard Model Higgs rates at the LHC which depend on the pT cuts applied and can be significant. There are also important consequences for physics beyond the Standard Model as the gg→hZ process introduces significant dependence on the magnitude and sign of the Higgs-top quark coupling ct, which is overlooked if it is assumed that associated production depends only on the Higgs-Z boson coupling as c2V. This new dependence on ct impacts interpretations of Higgs rates in the contexts of Supersymmetry, Two Higgs Doublet Models, and general scenarios with modified couplings. We suggest that these effects be included in current and future LHC boosted Higgs analyses.

3/19/2015, Hisakazu Minakata: "Oscillations of the 7Be solar neutrinos inside the Earth" (joint JC @USP)

References: 1503.02183

Abstract (of the paper): We explore in detail oscillations of the solar 7Be neutrinos in the matter of the Earth. The depth of oscillations is about (0.1−0.2)% and the length ≈30 km. The period of the oscillatory modulations in the energy scale is comparable with the width of the line determined by the temperature in the center of the Sun. The latter means that depending on the length of trajectory (nadir angle) one obtains different degree of averaging of oscillations. Exploring these oscillations it is possible to measure the width of the 7Be line and therefore the temperature of the Sun, determine precisely Δm221, perform tomography of the Earth, in particular, measure the deviation of its form from sphere, and detect small structures. Studies of the Be neutrinos open up a possibility to test quantum mechanics of neutrino oscillations and search for the sterile neutrinos. Accuracy of these measurements with future scintillator (or scintillator uploaded) detectors of the ∼100 kton mass scale is estimated.

3/26/2015, Rogério Rosenfeld: "Naturalness in the Dark at the LHC"

References: 1501.05310

Abstract (of the paper): We revisit the Twin Higgs scenario as a "dark" solution to the little hierarchy problem, identify the structure of a minimal model and its viable parameter space, and analyze its collider implications. In this model, dark naturalness generally leads to Hidden Valley phenomenology. The twin particles, including the top partner, are all Standard-Model-neutral, but naturalness favors the existence of twin strong interactions -- an asymptotically-free force that confines not far above the Standard Model QCD scale -- and a Higgs portal interaction. We show that, taken together, these typically give rise to exotic decays of the Higgs to twin hadrons. Across a substantial portion of the parameter space, certain twin hadrons have visible and often displaced decays, providing a potentially striking LHC signature. We briefly discuss appropriate experimental search strategies.

4/2/2015, Diogo Boito: "An Effective Guide to Beyond the Standard Model Physics" (joint JC @IFT)

References: 1406.6376

Abstract (of the paper): Effective Lagrangians with dimension-six operators are widely used to analyse Higgs and other electroweak data. We show how to build a basis of operators such that each operator corresponds to a coupling which is well measured or will be in the future. We choose a set of couplings such that the correspondence is one-to-one. In our framework, some important features of the Lagrangian are transparent. For example, one can clearly see the presence or absence of correlations among measurable quantities. This may be a useful guide when searching for physics beyond the Standard Model.

4/9/2015, Claudio Dib: "Heavy neutrinos and displaced vertices at the LHC"

We study several processes where heavy neutral leptons (i.e heavy sterile neutrinos) could be detected:
Several Lepton-Number violating meson decays, such as D^+ -> pi^- e^+ e^+, are induced by heavy neutral leptons in the intermediate state. These can enhance the rates when the mass is such that the neutral lepton goes on mass shell. However this implies long lifetimes (and long vertex displacements), requiring long detectors to observe the effect.

We also present the production and decays of neutral leptons at the LHC, also considering displaced vertices. The LHC is sensitive to heavier neutrals, with shorter lifetimes. Still there are significant vertex displacements, but here this effect can help reduce backgrounds.

Some references:
- Probing Majorana neutrinos in rare K and D, ~D_s, B, B_c meson decays,
G. Cvetic, C.D., Sin Kyu Kang, C.S. Kim
Phys.Rev. D82 (2010) 053010
e-Print: arXiv:1005.4282 [hep-ph]

-Remarks on the lifetime of sterile neutrinos and the effect on detection of rare meson decays M+→M′−ℓ+ℓ+
C.D., C.S. Kim
Phys.Rev. D89 (2014) 7, 077301
e-Print: arXiv:1403.1985 [hep-ph]

-Heavy neutrino searches at the LHC with displaced vertices
Juan C. Helo, Martin Hirsch, Sergey Kovalenko,
Phys.Rev. D89 (2014) 7, 073005
e-Print: arXiv:1312.2900 [hep-ph]

-Proposal to Search for Heavy Neutral Leptons at the SPS
W. Bonivento et al.
CERN-SPSC-2013-024, SPSC-EOI-010
e-Print: arXiv:1310.1762 [hep-ex]

- Left-Right Symmetric Models with GeV heavy neutrinos at High-Intensity Frontier
O. Castillo-Felisola, C.D, J. Helo, S. Kovalenko, and S. Ortiz
...in preparation

4/16/2015, Chee Sheng Fong: "Highlight talk on EW Moriond 2015" (joint JC @USP)

References: Talks

A highlight of what happened on Moriond 2015

4/23/2015, Camila Machado: "Implications of b→s measurements"

References: 1503.06199 and 1411.3161

Abstract (of the paper): The recent updated angular analysis of the  BK μ + μ  decay by the LHCb collaboration is interpreted by performing a global fit to all relevant measurements probing the flavour-changing neutral current  bsμ + μ  transition. A significant tension with Standard Model expectations is found. A solution with new physics modifying the Wilson coefficient  C 9  is preferred over the Standard Model by  3.7σ . The tension even increases to  4.2σ  including also  bse + e  measurements and assuming new physics to affect the muonic modes only. Other new physics benchmarks are discussed as well. The  q 2  dependence of the shift in  C 9  is suggested as a means to identify the origin of the tension - new physics or an unexpectedly large hadronic effect.

4/30/2015, 5:00 PM, Nicolás Bernal: "Dark Matter Self-Interactions" (joint JC @IFT)

References: 1503.07675 and 1504.03388

Abstract (of the paper): Collisions between galaxy clusters provide a test of the non-gravitational forces acting on dark matter. Dark matter's lack of deceleration in the `bullet cluster collision' constrained its self-interaction cross-section \sigma_DM/m < 1.25cm2/g (68% confidence limit) for long-ranged forces. Using the Chandra and Hubble Space Telescopes we have now observed 72 collisions, including both `major' and `minor' mergers. Combining these measurements statistically, we detect the existence of dark mass at 7.6\sigma significance. The position of the dark mass has remained closely aligned within 5.8+/-8.2 kpc of associated stars: implying a self-interaction cross-section \sigma_DM/m < 0.47 cm2/g (95% CL) and disfavoring some proposed extensions to the standard model.

5/7/2015, Leonardo de Lima: "Consistent Use of the Standard Model Effective Potential"

References: 1408.0292

Abstract (of the paper): The stability of the Standard Model is determined by the true minimum of the effective Higgs potential. We show that the potential at its minimum when computed by the traditional method is strongly dependent on the gauge parameter. It moreover depends on the scale where the potential is calculated. We provide a consistent method for determining absolute stability independent of both gauge and calculation scale, order by order in perturbation theory. This leads to a revised stability bounds mH > (129.4 \pm 2.3) GeV and mt < (171.2 \pm 0.3)GeV. We also show how to evaluate the effect of new physics on the stability bound without resorting to unphysical field values.

5/14/2015, Oscar Eboli: "Cornering dimension-6 HVV interactions at high luminosity LHC: the role of event ratios" (joint JC @USP)

References: 1505.00226

Abstract (of the paper): We suggest a way of improving the probes on dimension-6 CP-conserving  H V V  interactions ( V  =  W Z γ ), from the LHC data on the Higgs boson to be available in the 14 TeV run with an integrated luminosity of  3000  fb 1 . We find that the ratios of total rates in different channels can be quite useful in this respect. This includes ratios of event rates in (a) different final states for the Higgs produced by the same production mechanism, and (b) the same final state from two different production modes. While most theoretical uncertainties cancel in the former, the latter helps in the case of those operators which shift the numerator and denominator in opposite directions. Our analysis, incorporating theoretical, systematic and statistical uncertainties, leads to projected limits that are better than the strongest ones obtained so far from precision electroweak as well as LHC Higgs data. Moreover, values of the coefficients of the dimension-6 operators, which are allowed in disjoint intervals, can have their ranges narrowed down substantially in our approach.

5/21/2015, Gero von Gersdorff: "Cosmological Relaxation of the Electroweak Scale"

References: 1504.07551

Abstract (of the paper): A new class of solutions to the electroweak hierarchy problem is presented that does not require either weak scale dynamics or anthropics. Dynamical evolution during the early universe drives the Higgs mass to a value much smaller than the cutoff. The simplest model has the particle content of the standard model plus a QCD axion and an inflation sector. The highest cutoff achieved in any technically natural model is 10^8 GeV.

5/28/2015, Eduardo Pontón: "The cosmological Higgstory of the vacuum instability" (joint JC @IFT)

References: 1505.04825

Abstract (of the paper): The Standard Model Higgs potential becomes unstable at large field values. After clarifying the issue of gauge dependence of the effective potential, we study the cosmological evolution of the Higgs field in presence of this instability throughout inflation, reheating and the present epoch. We conclude that anti-de Sitter patches in which the Higgs field lies at its true vacuum are lethal for our universe. From this result, we derive upper bounds on the Hubble constant during inflation, which depend on the reheating temperature and on the Higgs coupling to the scalar curvature or to the inflaton. Finally we study how a speculative link between Higgs meta-stability and consistence of quantum gravity leads to a sharp prediction for the Higgs and top masses, which is consistent with measured values.

6/11/2015, Ricardo Matheus: "Unitarity-controlled resonances after Higgs discovery"

References: 1503.07459

Abstract (of the paper): If the recently discovered Higgs boson's couplings deviate from the Standard Model expectation, we may anticipate new resonant physics in the weak boson fusion channels resulting from high scale unitarity sum rules of longitudinal gauge boson scattering. Motivated by excesses in analyses of multi-leptons+missing energy+jets final states during run 1, we perform a phenomenological investigation of these channels at the LHC bounded by current Higgs coupling constraints. Such an approach constrains the prospects to observe such new physics at the LHC as a function of very few and generic parameters and allows the investigation of the strong requirement of probability conservation in the electroweak sector to high energies. Our analysis is directly relevant for the 2 TeV excess reported recently by the CMS and ATLAS collaborations.

6/18/2015, Encieh Erfani: "Inflation and Dark Matter Primordial Black Holes"

Abstract: Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations caused by Inflation in the early universe. A broad range of single field models of inflation are analyzed in light of all relevant recent cosmological data, checking whether they can lead to the formation of longlived PBHs as candidate for dark matter. To that end we calculate the spectral index of the power spectrum of primordial perturbations as well as its first and second derivatives. PBH formation is possible only if the spectral index ns(k0) increases significantly at small scales. Since current data indicate that the first derivative αs of the spectral index is negative at the pivot scale, PBH formation is only possible in the presence of a sizable and positive second derivative (running of the running) βs. Among the studied models, only the running-mass model allows PBH formation. As a by-product, we also show that the nonproduction of (long-lived) PBHs puts a stronger upper bound on βs.

7/2/2015, Luca Panizzi: "Phenomenology of new heavy quarks at the LHC"

Abstract: New heavy quarks are predicted in various scenarios of new physics; depending on their nature they can mix with SM quarks or they can even mediate the production of dark matter states. Theoretically-motivated scenarios of new physics in general predict the existence of multiple new quarks with different couplings with the SM states or dark matter. Experimental searches of new quarks at the LHC, on the other hand, have so far mostly tested minimal extensions of the SM with new quarks which specific decay patterns. No signals have been detected, pushing mass limits above 600-800 GeV, depending on different assumptions about their couplings to SM states. The reinterpretation of mass bounds from experimental searches to test theoretical models is therefore not always straightforward. I will describe model independent methods to recast data from experimental searches. These methods can be used to test general scenarios with any number of extra quarks which can mix with all SM families or couple to dark matter.

Joint JCs

These are the dates and places for the Joint JCs for this semester:

(January 29th) Joint JC @IFT, 2:00 PM
(February 12th) Joint JC @USP, 5:30 PM
(March 5th) Joint JC @IFT, 2:00 PM
(March 19th) Joint JC @USP, 5:30 PM
(April 2nd) Joint JC @IFT, 2:00 PM
(April 16th) Joint JC @USP, 5:30 PM
(April 30th) Joint JC @IFT, 2:00 PM
(May 14th) Joint JC @USP, 5:30 PM
(May 28th) Joint JC @IFT, 2:00 PM

Seminars

2/6/2015, 2:00 pm, Nayara Fonseca (IFUSP / CTP-MIT): "Dark Matter Constraints on Composite Higgs Models"

2/6/2015, 2:00 pm, Room 3, 3rd floor

Abstract: In composite Higgs models the pseudo-Nambu-Goldstone Boson (pNGB) nature of the Higgs field is an interesting alternative for explaning the smallness of the electroweak scale with respect to the beyond the Standard Model scale. In non-minimal models additional pNGB states are present and can be a Dark Matter (DM) candidate, if there is an approximate symmetry suppressing their decay. Here we assume that the low energy effective theory (for scales much below the compositeness scale) corresponds to the Standard Model with a pNGB Higgs doublet and a pNGB DM multiplet. We derive general effective DM Lagrangians for several possible DM representations (under the SM gauge group), including the singlet, doublet and triplet cases. Within this framework we discuss how the DM observables (relic abundance, direct and indirect detection) constrain the dimension-6 operators induced by the strong sector assuming that DM behaves as a Weakly Interacting Particle (WIMP) and that the relic abundance is settled through the freeze-out mechanism. We also apply our general results to two specific cosets: SO(6)/SO(5) and SO(6)/SO(4)×SO(2), which contain a singlet and doublet DM candidate, respectively. In particular we show that if compositeness is a solution to the little hierarchy problem, representations larger than the triplet are strongly disfavored. Furthermore, we find that composite models can have viable DM candidates with much smaller direct detection cross-sections than their non-composite counterparts, making DM detection much more challenging.

References: 1501.05957

3/5/2015, 2:00 pm, Maury Goodman (Argonne): "Status of the Experiment at the Long-Baseline Neutrino Facility ELBNF"

3/5/2015, 2:00 pm, Room 3, 3rd floor

ELBNF is part of an ambitious worldwide program to understand the neutrino. It will consist of a 40-kt modular liquid argon TPC located deep underground. The principal goals are to carry out a comprehensive investigation of neutrino oscillations to test CP violation in the lepton sector, to determine the ordering of the neutrino masses, and to test the three neutrino paradigm; to perform a broad set of neutrino scattering measurements with the near detector; and to exploit the large, high-resolution, underground far detector for non-accelerator physics topics, including atmospheric neutrino measurements, searches for nucleon decay, and measurement of astrophysical neutrinos, especially those from a core-collapse supernova.

4/9/2015, 2:00 pm, Claudio Dib (Universidad Tecnica Federico Santa Maria): "Heavy neutrinos and displaced vertices at the LHC"

4/9/2015, 2:00 pm, Room 3, 3rd floor

We study several processes where heavy neutral leptons (i.e heavy sterile neutrinos) could be detected:
Several Lepton-Number violating meson decays, such as D^+ -> pi^- e^+ e^+, are induced by heavy neutral leptons in the intermediate state. These can enhance the rates when the mass is such that the neutral lepton goes on mass shell. However this implies long lifetimes (and long vertex displacements), requiring long detectors to observe the effect.

We also present the production and decays of neutral leptons at the LHC, also considering displaced vertices. The LHC is sensitive to heavier neutrals, with shorter lifetimes. Still there are significant vertex displacements, but here this effect can help reduce backgrounds.

Some references:
- Probing Majorana neutrinos in rare K and D, ~D_s, B, B_c meson decays,
G. Cvetic, C.D., Sin Kyu Kang, C.S. Kim
Phys.Rev. D82 (2010) 053010
e-Print: arXiv:1005.4282 [hep-ph]

-Remarks on the lifetime of sterile neutrinos and the effect on detection of rare meson decays M+→M′−ℓ+ℓ+
C.D., C.S. Kim
Phys.Rev. D89 (2014) 7, 077301
e-Print: arXiv:1403.1985 [hep-ph]

-Heavy neutrino searches at the LHC with displaced vertices
Juan C. Helo, Martin Hirsch, Sergey Kovalenko,
Phys.Rev. D89 (2014) 7, 073005
e-Print: arXiv:1312.2900 [hep-ph]

-Proposal to Search for Heavy Neutral Leptons at the SPS
W. Bonivento et al.
CERN-SPSC-2013-024, SPSC-EOI-010
e-Print: arXiv:1310.1762 [hep-ex]

- Left-Right Symmetric Models with GeV heavy neutrinos at High-Intensity Frontier
O. Castillo-Felisola, C.D, J. Helo, S. Kovalenko, and S. Ortiz
...in preparation

6/18/2015, 2:00 pm, Encieh Erfani (Institute for Research in Fundamental Sciences - IPM, Iran): "Inflation and Dark Matter Primordial Black Holes"

6/18/2015, 2:00 pm, Room 3, 3rd floor

Abstract: Primordial Black Holes (PBHs) are gravitationally collapsed objects that may have been created by density fluctuations caused by Inflation in the early universe. A broad range of single field models of inflation are analyzed in light of all relevant recent cosmological data, checking whether they can lead to the formation of longlived PBHs as candidate for dark matter. To that end we calculate the spectral index of the power spectrum of primordial perturbations as well as its first and second derivatives. PBH formation is possible only if the spectral index ns(k0) increases significantly at small scales. Since current data indicate that the first derivative αs of the spectral index is negative at the pivot scale, PBH formation is only possible in the presence of a sizable and positive second derivative (running of the running) βs. Among the studied models, only the running-mass model allows PBH formation. As a by-product, we also show that the nonproduction of (long-lived) PBHs puts a stronger upper bound on βs.

7/2/2015, 2:00 pm, Luca Panizzi (University of Southampton): "Phenomenology of new heavy quarks at the LHC"

7/2/2015, 2:00 pm, Room 3, 3rd floor

Abstract: New heavy quarks are predicted in various scenarios of new physics; depending on their nature they can mix with SM quarks or they can even mediate the production of dark matter states. Theoretically-motivated scenarios of new physics in general predict the existence of multiple new quarks with different couplings with the SM states or dark matter. Experimental searches of new quarks at the LHC, on the other hand, have so far mostly tested minimal extensions of the SM with new quarks which specific decay patterns. No signals have been detected, pushing mass limits above 600-800 GeV, depending on different assumptions about their couplings to SM states. The reinterpretation of mass bounds from experimental searches to test theoretical models is therefore not always straightforward. I will describe model independent methods to recast data from experimental searches. These methods can be used to test general scenarios with any number of extra quarks which can mix with all SM families or couple to dark matter.

2015, 2nd semester

Journal Club Sessions

8/13/2015, Nayara Fonseca: "Dark Matter, Shared Asymmetries, and Galactic Gamma Ray Signals" (joint JC @IFT)

References: 1507.08295

Abstract (of the paper): We introduce a novel dark matter scenario where the visible sector and the dark sector share a common asymmetry. The two sectors are connected through an unstable mediator with baryon number one, allowing the standard model baryon asymmetry to be shared with dark matter via semi-annihilation. The present-day abundance of dark matter is then set by thermal freeze-out of this semi-annihilation process, yielding an asymmetric version of the WIMP miracle as well as promising signals for indirect detection experiments. As a proof of concept, we find a viable region of parameter space consistent with the observed Fermi excess of GeV gamma rays from the galactic center.

8/27/2015, Enrico Bertuzzo: "Is the Higgs Mechanism of Fermion Mass Generation a Fact? A Yukawa-less First-Two-Generation Model" (joint JC @USP)

References: 1508.01501

Abstract (of the paper): It is now established that the major source of electroweak symmetry breaking (EWSB) is due to the observed Higgs particle. However, whether the Higgs mechanism is responsible for the generation of all the fermion masses, in particular, the fermions of the first two generations, is an open question. In this letter we present a construction where the light fermion masses are generated through a secondary, subdominant and sequestered source of EWSB. This fits well with the approximate U(2) global symmetry of the observed structure of the flavor sector. We first realize the above idea using a calculable two Higgs doublet model. We then show that the first two generation masses could come from technicolor dynamics, while the third generation fermions, as well as the electroweak gauge bosons get their masses dominantly from the Higgs mechanism. We also discuss how the small CKM mixing between the first two generations and the third generation, and soft mixing between the sequestered EWSB components arise in this setup. A typical prediction of this scenario is a significant reduction of the couplings of the observed Higgs boson to the first two generation of fermions.

9/3/2015, Rogério Rosenfeld: "Composite Higgses with seesaw EWSB"

References: 1508.06133

Abstract (of the paper): We introduce a new class of Composite Higgs models in which electroweak symmetry is broken by a seesaw-like mechanism. If a global symmetry is broken sequentially at different scales, two sets of pseudo-Goldstone bosons will arise, one set being typically heavier than the other. If two Composite Higgs doublets mix, then the mass-squared of the lighter state can be driven negative, and induce EWSB. We illustrate with the example SO(6)→SO(5)→SO(4), and derive an estimate of the light Higgs potential. We find that the introduction of an extra scale can ease many of the tensions present in conventional Composite Higgs models, especially those related to fine-tuning. In particular we find that we can significantly raise the upper bound on the mass of the elusive top partners.

9/10/2015, Chee Sheng Fong: "Baryogenesis from Symmetry Principle" (joint JC @IFT)

References: 1508.03648

Abstract (of the paper): In this work, a formalism based on symmetry which allows one to express asymmetries of all the particles in terms of conserved charges is developed. The manifestation of symmetry allows one to easily determine the viability of a baryogenesis scenario and also to identity the different roles played by the symmetry. This formalism is then applied to the standard model and its supersymmetric extension, which constitute two important foundations for constructing models of baryogenesis.

9/24/2015, Sylvain Fichet: "Anatomy of the Higgs fits: a first guide to statistical treatments of the theoretical uncertainties"

References: 1509.00472

Abstract (of the paper): The studies of the Higgs boson couplings based on the recent and upcoming LHC data open up a new window on physics beyond the Standard Model. In this paper, we propose a statistical guide to the consistent treatment of the theoretical uncertainties entering the Higgs rate fits. Both the Bayesian and frequentist approaches are systematically analysed in a unified formalism. We present analytical expressions for the marginal likelihoods, useful to implement simultaneously the experimental and theoretical uncertainties. We review the various origins of the theoretical errors (QCD, EFT, PDF, production mode contamination...). All these individual uncertainties are thoroughly combined with the help of moment-based considerations. The theoretical correlations among Higgs detection channels appear to affect the location and size of the best-fit regions in the space of Higgs couplings. We discuss the recurrent question of the shape of the prior distributions for the individual theoretical errors and find that a nearly Gaussian prior arises from the error combinations. We also develop the bias approach, which is an alternative to marginalisation providing more conservative results. The statistical framework to apply the bias principle is introduced and two realisations of the bias are proposed. Finally, depending on the statistical treatment, the Standard Model prediction for the Higgs signal strengths is found to lie within either the  68% or  95%  confidence level region obtained from the latest analyses of the  7  and  8  TeV LHC datasets.

10/1/2015, Maria Eugenia Cabrera Catalan: "Dark Photons from the Center of the Earth: Smoking-Gun Signals of Dark Matter" (joint JC @USP)

References: 1509.07525

Abstract (of the paper): Dark matter may be charged under dark electromagnetism with a dark photon that kinetically mixes with the Standard Model photon. In this framework, dark matter will collect at the center of the Earth and annihilate into dark photons, which may reach the surface of the Earth and decay into observable particles. We determine the resulting signal rates, including Sommerfeld enhancements, which play an important role in bringing the Earth's dark matter population to their maximal, equilibrium value. For dark matter masses mX∼ 100 GeV - 10 TeV, dark photon masses mA′∼ MeV - GeV, and kinetic mixing parameters ε∼10^(−9)−10^(−7), the resulting electrons, muons, photons, and hadrons that point back to the center of the Earth are a smoking-gun signal of dark matter that may be detected by a variety of experiments, including neutrino telescopes, such as IceCube, and space-based cosmic ray detectors, such as Fermi-LAT and AMS. We determine the signal rates and characteristics, and show that large and striking signals---such as parallel muon tracks---are possible in regions of the (mA′,ε) plane that are not probed by direct detection, accelerator experiments, or astrophysical observations.

10/15/2015, Alessandro Codello: "Covariant Effective Field Theory of Gravity" (joint JC @IFT)

References: 1507.06308 and 1507.07829

Abstract: Using covariant methods we construct the effective field theory of gravity as a loop expansion in inverse powers of the Planck mass, distinguishing classical, leading and next-to-leading quantum corrections. We then compute the leading corrections in a curvature expansion to quadratic order. We specialize the effective action to FRW spacetimes and we derive the related effective Friedmann equations. We show that for particular values of the parameters we recover many different non-local modifications of general relativity recently proposed that are able to describe both early and late time cosmology.

October 19 to December 19: Program on Particle Physics at the Dawn of the LHC13

During this period we will have no Journal Club sessions. Instead we invite all our usual participants to take part in the activities of the Program on Particle Physics at the Dawn of the LHC13.

Details and schedule for the program can be found here: http://www.ictp-saifr.org/?page_id=9445

These are the dates and places for the Joint JCs for this semester:

(August 13th) Joint JC @IFT, 2:00 PM
(August 27th) Joint JC @USP, 5:30 PM
(September 10th) Joint JC @IFT, 2:00 PM
(October 1st) Joint JC @USP, 5:30 PM
(October 15th) Joint JC @IFT, 2:00 PM


Seminars

8/13/2015, 2:00 pm, Nayara Fonseca (IFUSP / CTP-MIT): "Dark Matter, Shared Asymmetries, and Galactic Gamma Ray Signals" (joint JC @IFT)

8/13/2015, 2:00 pm, Room 3, 3rd floor

References: 1507.08295

Abstract: We introduce a novel dark matter scenario where the visible sector and the dark sector share a common asymmetry. The two sectors are connected through an unstable mediator with baryon number one, allowing the standard model baryon asymmetry to be shared with dark matter via semi-annihilation. The present-day abundance of dark matter is then set by thermal freeze-out of this semi-annihilation process, yielding an asymmetric version of the WIMP miracle as well as promising signals for indirect detection experiments. As a proof of concept, we find a viable region of parameter space consistent with the observed Fermi excess of GeV gamma rays from the galactic center.

9/10/2015, 2:00 pm, Chee Sheng Fong (IFUSP): "Baryogenesis from Symmetry Principle" (joint JC @IFT)

9/10/2015, 2:00 pm, Room 3, 3rd floor

References: 1508.03648

Abstract: In this work, a formalism based on symmetry which allows one to express asymmetries of all the particles in terms of conserved charges is developed. The manifestation of symmetry allows one to easily determine the viability of a baryogenesis scenario and also to identity the different roles played by the symmetry. This formalism is then applied to the standard model and its supersymmetric extension, which constitute two important foundations for constructing models of baryogenesis.

9/24/2015, 2:00 pm, Sylvain Fichet (ICTP-SAIFR and International Institute of Physics, UFRN): "Anatomy of the Higgs fits: a first guide to statistical treatments of the theoretical uncertainties"

9/24/2015, 2:00 pm, Room 3, 3rd floor

References: 1509.00472

Abstract (of the paper): The studies of the Higgs boson couplings based on the recent and upcoming LHC data open up a new window on physics beyond the Standard Model. In this paper, we propose a statistical guide to the consistent treatment of the theoretical uncertainties entering the Higgs rate fits. Both the Bayesian and frequentist approaches are systematically analysed in a unified formalism. We present analytical expressions for the marginal likelihoods, useful to implement simultaneously the experimental and theoretical uncertainties. We review the various origins of the theoretical errors (QCD, EFT, PDF, production mode contamination...). All these individual uncertainties are thoroughly combined with the help of moment-based considerations. The theoretical correlations among Higgs detection channels appear to affect the location and size of the best-fit regions in the space of Higgs couplings. We discuss the recurrent question of the shape of the prior distributions for the individual theoretical errors and find that a nearly Gaussian prior arises from the error combinations. We also develop the bias approach, which is an alternative to marginalisation providing more conservative results. The statistical framework to apply the bias principle is introduced and two realisations of the bias are proposed. Finally, depending on the statistical treatment, the Standard Model prediction for the Higgs signal strengths is found to lie within either the  68% or  95%  confidence level region obtained from the latest analyses of the  7  and  8  TeV LHC datasets.

10/15/2015, 2:00 pm, Alessandro Codello (CP3 – Origins, Odense, Denmark): "Covariant Effective Field Theory of Gravity"

10/15/2015, 2:00 pm, Room 3, 3rd floor

References: 1507.06308 and 1507.07829

Abstract: Using covariant methods we construct the effective field theory of gravity as a loop expansion in inverse powers of the Planck mass, distinguishing classical, leading and next-to-leading quantum corrections. We then compute the leading corrections in a curvature expansion to quadratic order. We specialize the effective action to FRW spacetimes and we derive the related effective Friedmann equations. We show that for particular values of the parameters we recover many different non-local modifications of general relativity recently proposed that are able to describe both early and late time cosmology.

October 19 to December 19: Program on Particle Physics at the Dawn of the LHC13

During this period we will have no Journal Club sessions. Instead we invite all our usual participants to take part in the activities of the Program on Particle Physics at the Dawn of the LHC13.

Details and schedule for the program can be found here: http://www.ictp-saifr.org/?page_id=9445

2016, 1st semester

Journal Club Sessions

10/3/2016, Alberto Tonero: "What is the gamma gamma resonance at 750 GeV?" (joint JC @IFT)

References: 1512.04933

Abstract (of the paper): Run 2 LHC data show hints of a new resonance in the diphoton distribution at an invariant mass of 750 GeV. We analyse the data in terms of a new boson, extracting information on its properties and exploring theoretical interpretations. Scenarios covered include a narrow resonance and, as preliminary indications suggest, a wider resonance. If the width indications persist, the new particle is likely to belong to a strongly-interacting sector. We also show how compatibility between Run 1 and Run 2 data is improved by postulating the existence of an additional heavy particle, whose decays are possibly related to dark matter.

17/3/2016, Rafael Porto: "The Tune of Love: Black Holes and Naturalness"

Abstract: The hierarchy between the electroweak and Planck scale, the cosmological constant problem and the black hole information paradox are among the most vexing puzzles in theoretical physics. I argue there is yet another black hole quandary which, in light of the recent direct detection of gravitational waves by Advanced LIGO, reveals a new window to probe the nature of spacetime in the forthcoming era of 'precision gravity'.

31/3/2016, Eduardo Pontón: "Diphoton Resonance from a Warped Extra Dimension"

References: 1603.05978

Abstract (of the paper): We argue that extensions of the Standard Model (SM) with a warped extra dimension, which successfully address the hierarchy and flavor problems of elementary particle physics, can provide an elegant explanation of the 750 GeV diphoton excess recently reported by ATLAS and CMS. A gauge-singlet bulk scalar with O(1) couplings to fermions is identified as the new resonance S, and the vector-like Kaluza-Klein excitations of the SM quarks and leptons mediate its loop-induced couplings to photons and gluons. The electroweak gauge symmetry almost unambiguously dictates the bulk matter content and hence the hierarchies of the S→γγ, WW, ZZ, Zγ, t\bar t and dijet decay rates. We find that the S→Zγ decay mode is strongly suppressed, such that Br(S→Zγ)Br(S→γγ)<0.1. The hierarchy problem for the new scalar boson is solved in analogy with the Higgs boson by localizing it near the infrared brane. The infinite sums over the Kaluza-Klein towers of fermion states are finite and can be calculated in closed form with a remarkably simple result. Reproducing the observed pp→S→γγ signal requires Kaluza-Klein masses in the multi-TeV range, in perfect agreement with bounds from flavor physics and electroweak precision observables.

7/4/2016, Alexandre Alves: "Infering the Higgs Boson Mass with the Maximum Entropy Method" (joint JC @IFT)

Abstract: In this talk, I show how the Higgs boson mass and the vacuum expectation value can be inferred with high precision computing the information-theoretic entropy of the Higgs boson decay probabilities into Standard Model particles and using the maximum entropy principle.

14/4/2016, Nicolás Bernal: "The Dark Temperature"

References: SIMPs begin, SIMPs strike back, GB, FIMPs, ELDER and Cannibals

Abstract: Everything You Always Wanted to Know About the Dark Matter Temperature*
                But Were Afraid to Ask

21/4/2016, Tiradentes → No JC :-(

28/4/2016, Boris Panes: "New ambiguity in probing CP violation in neutrino oscillations" (Joint JC @USP)

Reference: 1604.05690

Abstract (of the paper):
If neutrinos get mass a la seesaw the mixing matrix describing neutrino oscillations can be effectively non-unitary. We show that in this case the neutrino appearance probabilities involve a new CP phase, φ, associated to non-unitarity. This leads to an ambiguity in extracting the "standard" three-neutrino phase δCP, which can survive even after neutrino and antineutrino channels are combined. Its existence should be taken into account in the planning of any oscillation experiment aiming at a robust measurement of δCP.

5/5/2016, Anibal Medina (Saclay): "Diphoton Excess at 750 GeV from a Radion in the Bulk-Higgs Scenario"

Reference: 1512.05618

Abstract: In this work we point out that the diphoton excess recently presented by the ATLAS and CMS collaborations might originate from a radion in the bulk Higgs scenario within a warped extra dimension. In this case the couplings of the radion to massive gauge bosons are suppressed, allowing it to evade existing searches. In the presence of mixing with the Higgs, due to the strong constraints from diboson searches, only points near what we denominate the alignment region are able to explain the diphoton signal and evade current experimental constraints. The radion always has a sizeable branching ratio into top pairs, which provides a somewhat model independent channel to probe this scenario in the near future. If alignment is strong however, there are regions of parameter space where diHiggs decays may dominate providing stronger constraints and interesting perspectives for future collider searches.

12/5/2016, Sylvain Fichet: "Disscusion about Polarizable Dark particles" (Joint JC @IFT)

Reference:
1206.2910

19/5/2016, Ricardo Matheus: "Recent developments in Relaxion models"

26/5/2016, Corpus christi → No JC :-(

2/6/2016, Enrico Bertuzzo: "Evidence for a Protophobic Fifth Force from 8Be Nuclear Transitions" (Joint JC @USP)

Reference: 1604.07411

Abstract (of the paper):
Recently a 6.8σ anomaly has been reported in the opening angle and invariant mass distributions of e+e- pairs produced in 8Be nuclear transitions. The data are explained by a 17 MeV vector gauge boson X that is produced in the decay of an excited state to the ground state, 8Be*8Be X, and then decays through X→e+e-. The X boson mediates a fifth force with a characteristic range of 12 fm and has milli-charged couplings to up and down quarks and electrons, and a proton coupling that is suppressed relative to neutrons. The protophobic X boson may also alleviate the current 3.6σ discrepancy between the predicted and measured values of the muon's anomalous magnetic moment.

9/6/2016, Thiago Tomei Fernandez: "A low-mass dark matter search using ionization signals in XENON100"

Reference: 1605.06262

Abstract (of the paper):
The paper extends the reach of the XENON100 experiment down to WIMP masses of 7 GeV, by forsaking the usage of a complete background model. They manage to set limits by considering that *every* event could be a signal event [???], which is what I found interesting. So, the first part of the talk will be a quick description of how XENON100 usually works; the second part will then be the different approach taken by this paper.

16/6/2016, Rogério Rosenfeld: "The diphoton as the Higgs of the Higgs" (Joint JC @IFT)

Reference: 1605.08681

Abstract (of the paper):
LHC results do not confirm conventional natural solutions to the Higgs mass hierarchy problem, motivating alternative interpretations where a hierarchically small weak scale is generated from a dimension-less quantum dynamics. We propose weakly and strongly-coupled models where the field that breaks scale invariance giving mass to itself and to the Higgs is identified with the 750 GeV diphoton resonance. Such models can be extrapolated up to the Planck scale, provide Dark Matter candidates and eliminate the SM vacuum instability.

23/6/2016, Bruce Sánchez-Vega: "A Brief Journey into Nambu-Goldstone Bosons"

Abstract:
In this short talk, I am going to show the role of the (pseudo) Nambu-Goldstone (NG) bosons in two different contexts. The first one is a framework where neutrino masses and axion like particles (ALPs) are related each other and at the same time, these offer a solution to some astrophysical anomalies. In the second one, I am going to consider the 331 model with different symmetry breaking patterns with NG bosons in the physical spectra. Mainly, I going to focus on the bounds that the existence of these NG bosons impose on that model.

30/6/2016, Dark Matter School → No JC :-(

7/7/2016, Dark Matter School → No JC :-(

14/7/2016, PPC → No JC :-(

21/7/2016, IFT-Perimeter-SAIFR Journeys → No JC :-(

Seminars

24/6/2016, 2:00 pm, Sergio Palomares-Ruiz (IFIC - Spain): "Subhalos internal structure and dark matter annihilation signals"

24/6/2016, 2:00 pm, Room 3, 3rd floor

Abstract: A prediction of the standard ΛCDM cosmological model, also confirmed by N-body simulations, is that dark matter halos are teeming with numerous self-bound substructure, or subhalos. In this talk, thanks to the superb subhalo statistics (in the mass range 106 - 1011 h-1 Msun) of the Via Lactea II and ELVIS Milky Way-size simulations, and by taking a profile-independent approach, I will present a study of subhalo properties as a function of the distance to the host halo center and subhalo mass. With this at hand, I present a refinement of the substructure boost model of Sanchez-Conde&Prada 2014.

2016, 2nd semester

Journal Club Sessions

25/8/2016, Alberto Tonero: "Constraining the Higgs couplings to up and down quarks using production kinematics at the CERN Large Hadron Collider"

Reference: 1608.04376

Abstract (of the paper): We study the prospects for constraining the Higgs boson's couplings to up and down quarks using kinematic distributions in Higgs production at the CERN Large Hadron Collider. We find that the Higgs pT distribution can be used to constrain these couplings with precision competitive to other proposed techniques. With 3000 fb−1 of data at 13 TeV in the four-lepton decay channel, we find ***, where +++ is a scaling factor that modifies the q quark Yukawa coupling relative to the Standard Model bottom quark Yukawa coupling. The sensitivity may be improved by including additional Higgs decay channels.

1/9/2016, Camila Machado: "Helicity Selection Rules and Non-Interference for BSM Amplitudes" (joint JC @IFT)

Reference: 1607.05236

Abstract (of the paper): Precision studies of scattering processes at colliders provide powerful indirect constraints on new physics. We study the helicity structure of scattering amplitudes in the SM and in the context of an effective Lagrangian description of BSM dynamics. Our analysis reveals a novel set of helicity selection rules according to which, in the majority of 2 → 2 scattering processes at high energy, the SM and the leading BSM effects do not interfere. In such situations, the naive expectation that dimension-6 operators represent the leading BSM contribution is compromised, as corrections from dimension-8 operators can become equally (if not more) important well within the validity of the effective field theory approach

8/9/2016, Encontrão → No JC :-(

15/9/2016, Eduardo Pontón: "Nonrelativistic Short-Distance Completions of a Naturally Light Higgs"

References: 1608.06937, 1608.06287, 1308.5967 and 0901.3775

Abstract (of the paper): Nonrelativistic scalar field theories can exhibit a natural cascading hierarchy of scales, protected by a hierarchy of polynomial shift symmetries. Using a simple model, we argue that a high-energy cross-over to such nonrelativistic behavior naturally leads to light scalars, and thus represents a useful ingredient for technically natural resolutions of scalar mass hierarchies, perhaps even the Higgs mass hierarchy puzzle.

22/9/2016, Boris Panes: "Constraining High-Energy Cosmic Neutrino Sources: Implications and Prospects" (joint JC @USP)

Reference: 1607.01601

Abstract (of the paper): We consider limits on the local (z=0) density (n0) of extragalactic neutrino sources set by the nondetection of steady high-energy neutrino sources producing >30 TeV muon multiplets in the present IceCube data, taking into account the redshift evolution, luminosity function and neutrino spectrum of the sources. We show that the lower limit depends weakly on source spectra and strongly on redshift evolution. We find n0>10−7 Mpc−3 for standard candle sources evolving rapidly, ns∝(1+z)3, and n0≳10−5 Mpc−3 for nonevolving sources. The corresponding upper limits on their neutrino luminosity are *** and ***, respectively. Applying these results to a wide range of classes of potential sources, we show that powerful blazar jets associated with active galactic nuclei are unlikely to be the dominant sources. For almost all other steady candidate source classes (including starbursts, radio galaxies, and galaxy clusters and groups), an order of magnitude increase in the detector sensitivity at ∼0.1−1 PeV will enable a detection (as point sources) of the few brightest objects. Such an increase, which may be provided by next-generation detectors like IceCube-Gen2 and an upgraded KM3NET, can improve the limit on n0 by more than two orders of magnitude. Future gamma-ray observations (by Fermi, HAWC and CTA) will play a key role in confirming the association of the neutrinos with their sources.

29/9/2016, Nicolás Bernal: "Cannibal Dark Matter - Yummy!"

Reference: 1607.03108

Abstract (of the paper): A hidden sector with a mass gap undergoes an epoch of cannibalism if number changing interactions are active when the temperature drops below the mass of the lightest hidden particle. During cannibalism, the hidden sector temperature decreases only logarithmically with the scale factor. We consider the possibility that dark matter resides in a hidden sector that underwent cannibalism, and has relic density set by the freeze-out of two-to-two annihilations. We identify three novel phases, depending on the behavior of the hidden sector when dark matter freezes out. During the cannibal phase, dark matter annihilations decouple while the hidden sector is cannibalizing. During the chemical phase, only two-to-two interactions are active and the total number of hidden particles is conserved. During the one way phase, the dark matter annihilation products decay out of equilibrium, suppressing the production of dark matter from inverse annihilations. We map out the distinct phenomenology of each phase, which includes a boosted dark matter annihilation rate, new relativistic degrees of freedom, warm dark matter, and observable distortions to the spectrum of the cosmic microwave background.

6/10/2016, David Pinner: "Unification and New Particles at the LHC" (joint JC @IFT)

13/10/2016, Gero von Gersdorff: "The Global Higgs as a Signal for Compositeness at the LHC"

This talk is part of the "Program on Particle Physics at the New Energy Frontier of 13 TeV".

Abstract: We consider scenarios of Higgs compositeness where the Higgs doublet arises as a pseudo-Nambu Goldstone boson. Our focus is the physical scalar ("radial") excitation associated with the global symmetry breaking vacuum, which we call the "global Higgs". We derive the various couplings of this particle to the SM fields and show that in a wide class of Composite Higgs models studied in the literature the coupling of the global Higgs to gluons can be sizeable. We then investigate in detail some of the LHC signatures of the global Higgs.

20/10/2016, Enrico Bertuzzo: "Energy helps accuracy: electroweak precision tests at hadron colliders" (joint JC @USP)

Reference: 1609.08157

Abstract (of the paper): We show that high energy measurements of Drell-Yan at the LHC can serve as electroweak precision tests. Dimension-6 operators, from the Standard Model Effective Field Theory, modify the high energy behavior of electroweak gauge boson propagators. Existing measurements of the dilepton invariant mass spectrum, from neutral current Drell-Yan at 8 TeV, have comparable sensitivity to LEP. We propose measuring the transverse mass spectrum of charged current Drell-Yan, which can surpass LEP already with 8 TeV data. The 13 TeV LHC will elevate electroweak tests to a new precision frontier.

27/10/2016, Congresso Paulo Leal Ferreira → No JC :-(

3/11/2016, Alexander Belyaev: "Towards Dark Matter Spin Characterization at the LHC"

This talk is part of the "Program on Particle Physics at the New Energy Frontier of 13 TeV".

Abstract: The determination of the nature of Dark Matter (DM) is one of the most fundamental problems of particle physics and cosmology. If DM is light enough and interacts with Standard Model particles directly or via some mediators with a strength beyond the gravitational one, it can be directly produced at the Large Hadron Collider or future particle accelerators. The typical signature from DM produced in particles collisions is missing transverse energy, MET, due to the fact that they escape undetected from the experimental apparatus. We present study for the complete set of dimension 5 and dimension 6 effective operators involving scalar, fermion and vector DM to explore the possibility to distinguish these operators and characterise the spin of DM. We have found that, depending on the spin of the DM, the DM parts of the effective operators lead to a different energy dependence of the cross-sections and to different distributions of the invariant mass of the DM pair, and consequently to different MET distributions. Using statistical analysis, we have found that at the LHC with high luminosity, certain classes of EFT operators can be distinguished from each other and, through this, it is possible to characterise the spin of DM in some cases. We have also observed a drastic difference in the efficiencies (up to two orders of magnitude) for large MET cuts scenarios with different DM spin, thus indicating that the DM discovery potential strongly depends on it. The study we perform here can be applied more generally than within the EFT paradigm, where the DM mediator is not produced on-the-mass-shell, where the invariant mass of the DM pair is not fixed.

10/11/2016, Ricardo Matheus: "Phenomenology of relaxion-Higgs mixing" (Joint JC @IFT)

Reference: 1608.06937

17/11/2016, SILAFAE → No JC :-(

24/11/2016, Mini Workshop @USP on 25/11/2016 → No JC :-(

For more information about the mini-workshop click here.

01/12/2016, New Physics in Space Workshop → No JC :-(

08/12/2016, Sylvain Fichet: "Symmetry and Action for Flavor-Kinematics Duality"

Reference: 1612.00868

Seminars