Laboratoire de Physique
Theorique d'Orsay

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Univ. Paris-Sud 11
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Particle Physics Seminar

Particle physics seminars generally take place Thursdays at 4 PM, in room 114, 1st floor of Building 210.

Contact : Adam Falkowski.

Les séminaires se tiennent en salle 114 au 1er étage du bâtiment 210, généralement le jeudi à 16h, sauf indication contraire.

Upcoming Seminars

-  Thu 27 April 2017, 16:00, Pyungwon Ko (KIAS Seoul) : Dark gauge theories for dark matter and dark radiation

-  Thu 4 May 2017, 16:00, Andrei Angelescu (LPT Orsay) : TBA

-  Thu 11 May 2017, 16:00, Olcyr Sumensari (LPT Orsay) : TBA

-  Thu 18 May 2017, 16:00, Vittorio Lubicz (Universita Roma Tre) : Electromagnetic corrections to hadronic decays from lattice QCD

A new method recently introduced for the lattice calculation of electromagnetic and isospin corrections to weak decays is discussed. Using this method, for the first time, the electromagnetic effects in the leptonic decay rates π→μν and K→μν have been evaluated in lattice QCD. Results for the electromagnetic corrections to charged (neutral) pion and kaon masses and leptonic decay rates are presented.

-  Thu 1 June 2017, 16:00, Matias Rodriguez-Vazquez (LPT Orsay) : TBA

Past Seminars

-  Thu 20 April 2017, 16:00, Zahra Tabrizi (University of Sao Paulo) : Neutrinophilic Two-Higgs-Doublet Model as UV completion for inverse seesaw mechanism

More than two decades of neutrino experiments have confirmed that neutrinos are massive particles and oscillate. The seesaw mechanism is one of the most elegant and economic ways to explain the smallness of neutrino masse, however, it is inaccessible to current experiments. An interesting variation of the mechanism, which allows for TeV New Physics (NP), is given by the (double) inverse seesaw mechanism. In this work we show how the idea of neutrinophilic Two-Higgs-Doublet Model (ν2HDM) can be used to build a realistic and phenomenologically viable inverse seesaw model. We impose theoretical and experimental constrains on the model and show that while it is not difficult to have a phenomenologically viable neutrino physics, the parameter space is strongly constrained by the Higgs and Z boson decays and by electroweak precision tests.

-  Thu 6 April 2017, 16:00, Roberto Vega-Morales (University of Granada) : LHC Probes of SM-like and Exotic Higgs Sectors

In this talk I give an overview of various probes of a Standard Model like Higgs boson as well as other exotic scalars which might be present in beyond the Standard Model scenarios of electroweak symmetry breaking. ​I​ ​first discuss using four lepton​ decays​ of the 125 GeV Higgs boson ​to ​probe 1-loop effects. I will also discuss diboson probes of exotic scalars which can be found in models of electroweak symmetry breaking with extended Higgs sectors. If time permits I will also briefly discuss Higgs lepton flavor violating decays ​to probe the flavor sector of the Little Higgs model with T-Parity.

-   Thu 30 March 2017, 16:00, Aritra Gupta (Harish-Chandra Research Institute, Allahabad) : Astrophysical neutrinos, PeV events at IceCube, and the Direct Detection of Dark Matter

In this talk, we discuss the implications of the premise that any new, relativistic, highly energetic neutral particle that interacts with quarks and gluons would create cascade-like events in the IceCube (IC) detector which would be observationally indistinguishable from neutral current deep-inelastic (DIS) scattering events due to neutrinos. Consequently, one reason for deviations, breaks or excesses in the expected astrophysical power-law neutrino spectrum could be the flux of such a particle. Motivated by features in the recent 1347-day IceCube high energy starting event (HESE) data, we focus on particular boosted dark matter (\chi) related realizations of this premise, where \chi is assumed to be much lighter than, and the result of, the slow decay of a massive scalar (\phi ) which constitutes a major fraction of the Universe’s dark matter (DM). We show that this hypothesis, coupled with a standard power-law astrophysical neutrino flux is capable of providing very good fits to the present data, along with a possible explanation of other features in the HESE sample : ie, a) the paucity of events beyond 2 PeV b) a spectral feature resembling a dip in the 400 TeV - 1 PeV region and c) an excess in the 50-100 TeV region. We also consider constraints from diffuse gamma ray backgrounds and find that it is indeed very restrictive.

-   Thu 23 March 2017, 16:00, Monalisa Patra (IRB Zagreb) : Constraints on the top-Higgs FCNC couplings at linear colliders using a generalized top spin analysis

The flavor changing couplings of the top quark with the Higgs Boson and the up/charm quark, through the production has been extensively studied in the LHC and limits obtained. The nature of these couplings can also be explored in the International Linear Collider, with the kinematics of the emitted from in production being sensitive to the chirality of the coupling. The nature of the couplings can also be studied through the construction of different top-spin observables in the context of generalised spin basis. Overall I will discuss in details the sensitivity of the ILC in obtaining a limit on these coupling, with its different choice of initial beam polarization.

-   Thu 2 March 2017, 16:00, Sylvain Fichet (ICTP-SAIFR, Sao Paulo) : The global Higgs as a signal for compositeness at the LHC

We consider scenarios of Higgs compositeness where the Higgs doublet arises as a pseudo-Nambu Goldstone boson. Our focus is the scalar ("radial") excitation associated with the global symmetry breaking vacuum, which we dubbed the "global Higgs”. We study the interactions of the global Higgs and show that in a wide class of Composite Higgs models its coupling to gluons can be sizable. Some LHC signatures of the global Higgs are then investigated, including decay channels into EW bosons, top quarks, and possibly boosted top partners.

-  Thu 23 February 2017, 16:00, Javi Serra (CERN) : R-axion at colliders

We present the effective theory of a generic class of hidden sectors where supersymmetry is broken together with an approximate R-symmetry at low energy. The light spectrum contains the gravitino and the pseudo-Nambu-Goldstone boson of the R-symmetry, the R-axion. We derive new model-independent constraints on the R-axion decay constant for R-axion masses ranging from GeV to TeV, which are of relevance for hadron colliders, lepton colliders and B-factories. The current bounds allow for the exciting possibility that the R-axion will be the first sign of SUSY. We point out the most distinctive signals of the R-axion, providing a new experimental handle on the properties of the hidden sector.

-  Fri 24 February 2017, 16:00, Savvas Zafeiropoulos (LNL Virginia) : Complex Langevin simulations of a finite density matrix model for QCD

We study a random matrix model for QCD at finite density via complex Langevin dynamics. This model has a phase transition to a phase with nonzero baryon density. We study the convergence of the algorithm as a function of the quark mass and the chemical potential and focus on two main observables : the baryon density and the chiral condensate. For simulations close to the chiral limit, the algorithm has wrong convergence properties when the quark mass is in the spectral domain of the Dirac operator. A possible solution of this problem is discussed.

-  Thu 16 February 2017, 16:00, Mariane Mangin-Brinet (LPSC Grenoble) : Markov Chain Monte Carlo technics applied to Parton Distribution Functions determination : proof of concept

Among the fundamental ingredients of QCD, Parton Distribution Functions (PDFs) are key elements and play an essential role to connect the QCD dynamics of quarks and gluons to the measured hard scattering cross sections of colliding hadron(s). They carry an invaluable source of information on hadrons partonic structure and enormous theoretical and experimental efforts since years have been devoted to the extraction of these distribution functions. We have developed a new procedure to determine these PDFs and their uncertainties, based on Markov Chain Monte Carlo methods. After a brief introduction to the challenges of PDFs determination, I will show in this seminar how we can replace the standard χ2 minimization used in global analyses by procedures grounded on Statistical methods, and on Bayesian inference in particular, thus offering additional insight into the rich field of PDFs.

-   Thu Dec 1 2016, 16:00, Yuri Dokshitser (LPTHE) : 40 years of Gluon Dynamics

We will discuss important steps in the history of QCD, as well as new perspectives in understanding the gluon interaction dynamics that are offered by Super-Symmetric QFTs.

Slides can be found under this link :

-   Thu Nov 24 2016, 16:00 (salle des conseils !), Antoine Gérardin (University of Mainz) : The pion to two-photon transition form factor and the hadronic light-by-light scattering in the muon g-2

I will present some new developments on the pion-pole contribution to the hadronic light-by-light scattering in the muon g−2 and how to better control the uncertainty of this contribution. This in particularly relevant in order to fully profit from future muon g-2 experiments to test the Standard Model and to constrain models of New Physics. In the framework of Lattice QCD, we are able to compute the pion to two-photon transition form factor in the kinematical range of interest [0−1.5] GeV^2 where no experimental data are available yet. I will compare our results to different phenomenological models proposed in the literature and to experimental data in the single-virtual case when one photon is on-shell. Finally, I will use our result to give a first lattice estimate of the pion-pole contribution to the hadronic light-by-light scattering in the muon g-2, expected to be numerically dominant.
-   Thu Nov 17 2016, 16:00, Venus Keus (University of Helsinki) : CP violating scalar Dark Matter

I will talk about scalar extensions of the Standard Model (SM) in which copies of the SM scalar SU(2) doublet are added to the scalar sector. These extra doublets either acquire a Vacuum Expectation Value (VEV) and hence are "active" or do not acquire a VEV and are "inert". I will talk about Dark Matter (DM) candidates arising from the inert sector, and discuss CP-violation in the active or inert sector. I will then show the affect of CP-violation on the DM relic density and constrain the parameter space using recent results from the Large Hadron Collider (LHC) and DM direct and indirect detection experiments.
-   Thu Nov 10 2016, 14:00, Nejc Kosnik (Jozef Stefan Institute, Ljubljana) : Identifying viable leptoquark scenarios of lepton universality violation

Lepton flavor universality in the Standard Model and hints of its violation in neutral (RK) and charged currents (RD( ?)) in B decays are presented. We discuss model independent features as well as several leptoquark scenarios which are well suited to fit current values of RK and/or RD( ?) We also comment on the constraints posed by existing and future lepton flavor violation constraints as well as on possibility of flavor violation in Higgs decays.

-   Thu Nov 3 2016, 15:00, Attilio Cucchieri (Universidade de Sao Paulo) : Simulating math with lattice gauge theories : Bloch’s theorem in minimal Landau gauge

-   Thu Oct 13 2016, 16:00, Pouya Bakhti (IPM, Tehran) : Determining neutrino oscillation parameters in presence of Non-Standard neutrino Interaction (NSI)

To measure the last unknown $3\nu$ oscillation parameter ($\delta$), several long baseline neutrino experiments have been designed or proposed. Recently it has been shown that turning on neutral-current Non-Standard Interactions (NSI) of neutrinos with matter can induce degeneracies that may even hinder the proposed state-of-the-art DUNE long baseline experiment from measuring the value of $\delta$. We study how the result of the proposed MOMENT experiment with a baseline of 150 km and $200 \rm MeV\rm MeV$ can help to solve the degeneracy induced by NSI and determine the true value of $\delta$. We also investigate the effects of charged-current NSIs at the source and at the detector in the simulated data for DUNE, while neglecting the neutral-current NSI at the propagation. We study the effects of NSI on the simultaneous measurements of $\theta_23$ and $\delta$ in the DUNE. We also find the potential of DUNE to constrain the relevant charged-current NSI parameters.

-   Thu Oct 6 2016, 16:00, Oleg ANTIPIN (IRB Zagreb) : Composite Dark matter

I will discuss models where Dark Matter candidates arise as composite states of a new confining gauge force, stable thanks to accidental symmetries. Restricting to renormalizable theories compatible with SU(5) unification, I will present models based on SU(N) and SO(N) gauge groups. The two gage groups lead to distinctive phenomenologies including potential observable electric and magnetic dipole moments of the DM candidate that lead to peculiar spin-independent and spin-dependent cross sections. Models allowing for Yukawa couplings give rise to electric dipole moments for the electron. Each model predicts a specific set of lighter composite scalars, possibly observable at colliders and the framework can be used to realize the cosmological relaxation of the electro-weak scale.

-   Thu Sep 29 2016, 16:00, Giovanna Cottin (Cambridge University) : Prompt Signals and Displaced Vertices in the NMSSM

In this talk, we study the LHC phenomenology of a model that combines Gauge Mediation and the Next-to-Minimal Supersymmetric Standard Model. The model possesses regions of parameter space where a longer-lived lightest neutralino decays inside the detector resulting in potential displaced vertex (DV) signatures. We investigate current bounds on sparticle masses and the discovery potential of the model, both via conventional searches and via searches for displaced vertices. I will comment on the reach of prompt searches and also summarise on current long-lived particle searches at the LHC, including details of the ATLAS multi-track DV+jets analysis we recast. We realise that the current DV searches cannot probe this model due to b−quarks in the final state. We show how the displaced vertex cuts might be relaxed in order to improve signal efficiency, while simultaneously applied prompt cuts reduce background, resulting in a much better sensitivity than either strategy alone and motivating a fully fledged experimental study.
-   Thu Sep 22 2016, 16:00, Yasaman Farzan (IPM Iran) : Viable models for large Non-Standard neutrino Interactions.

It has been recently shown that in the presence of non-standard neutrino interaction with matter, even with an effective coupling as small as 0.01 times the Fermi constant, the proposed long baseline experiments may lose their ability to extract the yet-unknown neutrino parameters such as the Dirac CP-violating phase or the octant of $\theta_23$. I will introduce models based on new $U(1)$ gauge symmetries with a sub-GeV gauge boson that give rise to both lepton flavor conserving and violating neutral current neutrino interaction with matter. I will then discuss various experimental constraints and suggest observations to test these models.

-   Tue Sep 27 2016, 16:00, Miha Nemevsek (Jožef Stefan Institute, Ljubljana) : Majorana Higgses at colliders

Abstract : The discovery of the Higgs boson and its relation to the mass of elementary particles still leaves open the question of the origin of neutrino mass. Majorana showed that neutrinos could be their own antiparticles and violate the lepton number. Searches for phenomenological consequences of Majorana neutrinos range from neutrino-less double beta decay to collider searches. We will show that the Higgs sector provides a viable new frontier with a good sensitivity to high scales of new interactions. Rare decays of the Higgs boson and production of additional scalar resonances through the Higgs portal may provide smoking gun signals. Their observation would test the spontaneous origin of neutrino masses in complete analogy with the SM Higgs and charged fermions.

-   Tue Sep 20 2016, 11:00, Ulrich Nierste (TTP Karlsruhe) : CP violation in D and K decays : road to discoveries ?

CP violation in charm decay is not discovered yet. Hadronic effects prevent reliable predictions of Standard-Model expectations for charm CP asymmetries. I present correlations between different CP asymmetries in D meson decays from which unknown hadronic quantities cancel. The analysis is based on SU(3) symmetry and includes linear SU(3) breaking. The second topic of my talk is direct CP violation in K-> pi pi decays : The measurement of the corresponding parameter epsilon’ disagrees with the Standard-Model prediction by 2.9 standard deviations. This discrepancy can be explained in the Minimal Supersymmetric Standard Model with squarks and gluinos with multi-TeV masses.

-   Tue Sep 13 2016, 16:00, Amit Chakraborty (Tata Institute, Mumbai) : Chasing New Physics in Stacks of Soft Tracks

In this talk, we will introduce a new variable $\xi$, namely the number of tracks associated with the primary vertex, which are not parts of the reconstructed objects such as jets/isolated leptons etc in the context of new physics searches in the channel monojet + missing transverse momentum (MET). In models such as in compressed supersymmetry, events are often characterized by a rather large number of soft partons from the cascade decays, none of which result in reconstructed objects. We find that $\xi$, binned in pT, can discriminate these new physics events from events due to Z+jets, the main background in the monojet + MET channel. We find that the information contained in soft tracks is largely uncorrelated with traditional variables such as the effective mass, MET, pT of the jet, etc. and, therefore, a MultiVariate analysis combining these variables help to increase the discovery potential by more than 200% (depending on the spectra, of course). Pileup robustness of this variable will also be discussed at the end.

-   Thu July 21 2016, 16:00, Felix Kahlhoefer (DESY) : Dark mediators and dark terminators - how to save the WIMP

A reliable comparison of different dark matter (DM) searches requires models that satisfy certain consistency requirements like gauge invariance and perturbative unitarity. As a well-motivated example, I will discuss two-mediator DM (2MDM). The model is based on a spontaneously broken U(1)’ gauge symmetry and contains a Majorana DM particle as well as two s-channel mediators, one vector (the Z’) and one scalar (the dark Higgs). The presence of the two mediators affects the phenomenology of the model in important ways, leading to additional constraints but also offering new ways to avoid thermal overproduction of dark matter. I will present a global scan over the parameters of the model and explore whether thermal DM can still be viable within this model.

-   Wed July 13 2016, 16:00, Renata Zukanovich Funchal (Sao Paulo U.) : New Physics and the Flavour Composition of IceCube’s High Energy Neutrino Flux

Since 2012 the IceCube detector in the South Pole has been observing an unexpected flux of neutrinos in the energy range from about 100 TeV to a few PeV, most probably coming from outside our galaxy. We will discuss in this talk what can be learned from this measurement and, in particular, we will discuss what kind of new physics can be investigated using the flavour content of this data.

-  Wed 15 June 2016, 16:00, Renaud Boussarie (LPT Orsay) : Diffractive production of dijets in DIS

We give an introduction to Balitsky’s shockwave formalism, which we then use to compute the impact factor for the production of a quark-antiquark pair in DIS at NLO accuracy in kt-factorization. Finally we apply this result to get the cross-section for the production of dijets in diffractive DIS.

-  Wed 8 June 2016, 16:00, Tony Gherghetta (University of Minnesota) : Naturalizing Supersymmetry with the Relaxion Mechanism

Tuned versions of supersymmetry can be naturalized by a two-field relaxion mechanism that does not depend on QCD dynamics and where the relaxion potential barrier height is controlled by a second axion-like field. During the cosmological evolution, the relaxion rolls with a nonzero field value that breaks supersymmetry and scans the soft supersymmetric mass terms. Electroweak symmetry is broken after the soft masses become of order the supersymmetric Higgs mass term and causes the relaxion to stop rolling for superpartner masses up to 10^9 GeV. This can explain the tuning in supersymmetric models, including split-SUSY models, while preserving the QCD axion solution to the strong CP problem. Besides predicting two very weakly-coupled axion-like particles, the supersymmetric spectrum may contain an extra Goldstino, which could be a viable dark matter candidate.

-  Tue 7 June 2016, 16:00, Nabarun Chakrabarty (Harish-Chandra Research Institute, Allahabad) : High-scale validity of two and three Higgs-doublet scenarios.

To the precision LHC has attained so far, it is difficult to predict if the observed Higgs around 125 GeV is the SM Higgs, or a Higgs originating from an extended Higgs sector with an SM alignment. Prototypes of such scenarios are models with extra scalar doublets. While a 2HDM is important from the flavor physics perspective, a 3HDM too can turn useful in predicting the observed fermion mass hierarchy and the mixings. We have investigated some such models from the perspective of high-scale validity under renormalization group. Apart from requiring that each of these models furnishes a Higgs @125 GeV, we have also imposed constraints coming from oblique parameters, signal strengths, dark matter observables and also neutrino mass. The results generate useful insight about the viability of these models.

-  Thu 26 May 2016, 16:00, Alberto Ramos (CERN) : Towards a precise and accurate non-perturbative determination of the strong coupling constant at the electroweak scale.

Relating the value of the strong coupling at the electroweak scale with the experimental value of hadronic quantities is a theoretical challenge that requires a non-perturbative formulation of the strong interactions. Lattice QCD provides an adequate theoretical framework to attack this problem. Our collaboration has developed a systematic strategy to connect non-perturbatively the low energy region of QCD with its high energy perturbative domain. After many years of applications to the pure gauge theory and two-flavour theory, we have applied this strategy to the three flavour theory. This study will allow us to determine $\alpha_s(M_Z)$ in a controlled and precise fashion. In this talk I wil present the current status of the project.

-  28 April 2016, 11:00, Tereza Mendes (Instituto de Fisica de Sao Carlos/Universidade de Sao Paulo) : Infrared Gluon and Ghost Propagators and Deconfinement in Yang-Mills Theories

We investigate numerically the long-distance properties of gluon and ghost propagators in Landau gauge on the lattice, for the SU(2) case. By considering electric and magnetic gluon propagators at nonzero temperature, we extract Debye screening masses and look for signs of deconfinement around the critical temperature. Our results are related to the zero-temperature behavior of infrared propagators for comparison.

-  21 April 2016, 11:00, Benjamin Fuks (LPTHE Paris) : Next-to-leading order predictions matched to parton showers for new physics

During the first LHC run, both the ATLAS and CMS collaborations have extensively investigated many different channels in order to get hints for new physics. Many of these searches are currently based on Monte Carlo simulations of the signals where leading-order matrix elements of different partonic multiplicities are matched to parton showers and merged. More sophisticated differential theoretical predictions are however always helpful for setting more accurate exclusion limits, possibly refining the search strategies, and measuring the model free parameters in case of a discovery. In this talk, I will discuss how the MadGraph5_aMC@NLO framework can provide a general platform for computing (differential) observables within many beyond the Standard Model theories at the next-to-leading order accuracy in QCD. I will present specific examples based on scenarios inspired by supersymmetry and on vector-like quark models.

-  Thu 14 April 2016, 16:00, Mark Goodsel (LPTHE Paris) : Tools for the phenomenology of scalars in generic theories

I will discuss the state-of-the art of the calculation of properties of the scalar sectors for generic renormalisable theories, in the context of the package SARAH, in particular how this applies to their masses, production and decays. I will also discuss the relevance for the possible 750 GeV excess.

-  25 February 2016, 16:00, T.N. Truong (Ecole Polytechnique) Is It Possible to Use Perturbation Theory for Soft Pion Physics ?

Non perturbative methods for strong interaction in the low energy region are reviewed : the Bethe- Schwinger Effective Range theory and the Sum Rules of the type Adler­-Weisberger, Drell­-Hearn- Gerasimov. Extending these works to the Effective Chiral Theory of the QCD Lagrangian, the difference between the Weinberg and Lehman approaches is analyzed. The Weinberg approach is purely perturbative while the Lehman approach is a combination of the perturbation technique and unitarity via the effective range method. It is suggested that the low energy pion form factor data can be used to test the difference between the Weinberg and Lehman methods. The unitarisation scheme used for this problem is the inverse amplitude and/or the Padé approximant method. The one loop amplitude (TNT 1988) and the two loop amplitude (Hannah 1998) were done. These two calculations show the importance of incorporating the unitarity condition for a low energy theory and also the possible connections between the quark model (which could be in principle derived from the QCD Lagrangian) and the Effective Low Energy chiral theory of the QCD Lagrangian. I shall discuss the implication of this work on the use of the lattice gauge theory.

-  18 February 2016, 16:00, Laura Covi FIMP and SuperWIMPs at LHC

We review the Dark Matter production based on very weak coupling and heavy particle decay called FIMP and SuperWIMPS mechanisms and the general possibility of a decaying Dark Matter candidate. We then have a look at specific models, e.g. the minimal decaying Dark Matter scenario and gravitino Dark Matter and discuss possible signals at the LHC.

-  4 February 2016, 16:00, Svetlana Fajfer LFU violation in heavy meson semileptonic decays

Presently in B physics there are three anomalies which might imply violation of lepton flavour universality. The processes of B-> D(*) l nu and B-> K mu+ mu- can be approached using effective Hamiltonian framework. After establishing deviations of the experimental results from the Standard Model prediction, models of New Physics can be used. We explain observed anomalies by adding new coloured bosons - leptoquarks to the Standard Model. The experimental constraints are used to constrain parameter space of new particles and consequences of this SM extension are discussed.

-  28 January 2016, 16:30, Michel Tytgat (ULB Brussels) Signatures from Scalar Dark Matter with a Vector-like Quark Mediator

We present a comprehensive study of a model where the dark matter is composed of a singlet real scalar that couples to the Standard Model predominantly via a Yukawa interaction with a light quark and a colored vector-like fermion. A distinctive feature of this scenario is that thermal freeze-out in the early universe may be driven by annihilation both into gluon pairs at one-loop (gg) and by virtual internal Bremsstrahlung of a gluon (qqg). Such a dark matter candidate may also be tested through direct and indirect detection and at the LHC ; viable candidates have either a mass nearly degenerate with that of the fermionic mediator or a mass above about 2 TeV.

-  17 December 2015, 4pm, Thomas Flacke (Korea University) Composite Higgs Models : on top partners, UV embeddings and collider phenomenology

Composite Higgs models provide a viable solution to the hierarchy problem. The models predict a new strongly coupled sector at the TeV scale which comes with virtues (discoverable new resonances at the LHC), problems (new sources of flavor violation) and new questions (``What is the underlying strongly coupled model ?’’). In the first part of the talk, I present results on the prospects to detect heavy vector-like resonances (``top partners’’) at LHC run 2. In the second part, I discuss a potential UV embedding leading to a viable composite Higgs model, and its phenomenological implications.

-  10 December 2015, 4pm, Diego Redigolo (LPTHE Jussieu) The Twin Higgs and its SUSY incarnations

After the Run I of LHC the common lore is that models of new physics are tuned at least at the 10% level. In such a situation it is fair to ask which models can saturate the fine tuning bound and what is the UV cutoff of these models. Around the cutoff scale we expect new physics states to be detectable at colliders. A special role in the plethora of new physics models is played by the Twin Higgs which gives a concrete (perturbative) realization of the so-called "Neutral Naturalness" paradigm where no new colored states are necessary to stabilize the EW scale. After a brief review of the basic Twin Higgs mechanism, I will discuss supersymmetric UV completions and their model building issues. I will show that many of the features of Twin SUSY models such as the Higgs mass constraint and the EWSB conditions can be discussed in a model independent way. This analysis can be used to compare different implementations of the Twin SUSY idea and identify promising directions.

-  4 December 2015, 2pm, Sylvain Fichet (Sao Paulo) Statistics for the Higgs

I will present a thorough treatment of the theoretical uncertainties in the fits of the Higgs couplings. These uncertainties should be increasingly relevant for the new physics search as the LHC accumulates data. The analysis will be put in a broad statistical context, including conceptual discussions and the development of new methods related to systematic uncertainties.

-  26 November 2015, 4pm, Sophie Renner (DAMTP Cambridge) Linear flavour violation and anomalies in B physics

There have been a series of measurements on the run I LHCb dataset that have shown some intriguing discrepancies from Standard Model predictions in decays of B mesons. I will introduce these measurements and their possible interpretations in terms of new tree level interactions. I will then describe a renormalizable model of new physics in which b->sll interactions arise at loop level. Many unwanted interactions are forbidden by accidental symmetries in the model, but a contribution to the anomalous magnetic moment of the muon is expected, which can be large enough to fit the measured value. I will discuss important flavour and direct search bounds, and explain how the flavour violation in the new physics couplings could be linked to that present in the Standard Model.

-  19 November 2015, 4pm, Filippo Sala (Jussieu) New physics at the TeV scale : extra Higgses and WIMP Dark Matter

The high energy physics community is in the process of deciding which machines to propose for fundings. It is then particularly important to study the discovery prospects of different models at such machines. In this talk, I will do so for two motivated cases : i) new physics is almost natural, and an extra singlet-like Higgs is the lightest new particle around (conceivable e.g. in the NMSSM and in Twin Higgs) ; ii) independently of naturalness, Dark Matter is an electroweak multiplet, the prototype of a WIMP. I will mainly focus on the reach of colliders in the first case, and of telescopes in the second one."

-  5 November 2015, 4pm, Javier Virto (Siegen U.) Fitting B decay anomalies

We have recently discovered a set of tensions in certain B decays, between the data collected during run 1 by the LHCb experiment and the SM predictions. I will review the status of this issue and its possible interpretations.

-  29 October 2015, 4pm, Admir Greljo (Zurich U.) Going beyond "kappa-framework" : Higgs Pseudo-observables

We define a set of pseudo-observables (PO) in Higgs decays that describe, in great generality, possible deviations from the Standard Model (SM). PO can be determined from experimental data, providing a systematic generalization of the "kappa-framework" so far adopted by the LHC experiments. PO are defined from on-shell decay amplitudes, allow for a systematic inclusion of higher-order QED and QCD corrections and can be computed in any Effective Field Theory (EFT) approach to Higgs physics. We implement PO in the Monte Carlo event generator for future phenomenological and experimental studies. We analyze the reduction of the number of independent PO following from the hypotheses of lepton-universality, CP invariance, custodial symmetry, and linearly realized electroweak (EW) symmetry breaking. In particular, we present a systematic evaluation of the bounds on the Higgs PO that follow from the electroweak precision in the linear EFT regime. We also discuss how to extend the framework to Higgs production.

-  22 October 2015, 4pm, Oleg Lebedev (Helsinki U.) The Higgs and cosmology

The Higgs field enjoys a special status in the Standard Model as it can couple to the hidden sector at the renormalizable level. I will discuss implications of such a coupling for dark matter and inflation.

-  15 October 2015, 4pm, Marco Taoso (Jussieu) Phenomenology of electroweak multiplets and the Galactic center excess.

Electroweak multiplets are arguably among the simplest and best motivated WIMP dark matter candidates. I will review their relevant phenomenology in the light of current and future experimental searches. Predictions for searches at the high-luminosity LHC, and at an 100 TeV pp collider will be presented. Then, I will focus on indirect detection probes. I will compare the predictions of the model with the most recent bounds, discussing the impact of astrophysical uncertainties on current constraints. Finally, I will present predictions for future surveys. In the last part of the talk, I will focus on searches of a generic WIMP candidate with gamma-ray observations of the galactic center. Recently, an excess of photons has been reported from that region of the sky. This signal has been proposed as a possible hint of WIMP annihilations. Here, I will critically review its derivation. In particular, I explore realistic background diffusion models, accounting for a possible enhancement of cosmic-ray sources in the galactic center region. I will show that, taking into account the aforementioned ingredient, the astrophysical emission reproduces the morphological features of the data in a wide energy range, and there is no longer evidence on an excess.

-  8 October 2015, Andreas Crivellin (CERN) New Physics in B decays and correlations with LHC searches

In this talk I review the recently observed anomalies in flavour physics in b->smumu, b->ctaunu and h->taumu. After an introduction to these observables, I discuss the various new physics explanations of these anomalies with focus on 2HDMs and Z’ prime models. Correlations among observables and the possible signatures at LHC searches are considered.

-  24 September 2015, Luca di Luzio (University of Genova) On the UV sensitivity of the SM vacuum decay rate

I review the formalism by which the tunneling probability of an unstable ground state can be computed in quantum field theory, with special reference to the Standard Model of electroweak interactions. I describe in some detail the approximations implicitly adopted in such calculation. Particular attention is devoted to the role of scale invariance, and to the different implications of scale-invariance violations due to quantum effects and possible new degrees of freedom.

-  7 September 2015, Jure Zupan (Cincinnati U.) Flavor violating Higgs decays

Flavor violating Higgs decays can be used as probes of new physics. Focusing mainly on the flavor violating leptonic Higgs decays I will first show what the model independent bounds on these decay modes are. In the second part of the talk I will discuss what kind of models could give the putative signal of h->tau mu hinted at in the CMS and ATLAS Run 1 data.

-  4 Juin 2015, Clara Peset (Barcelona Autonoma U.) On the proton radius puzzle

The proton radius was recently measured in muonic hydrogen spectroscopy giving a value that is 7-sigma (4.4%) away from its CODATA value, which is based on measurements coming both from hydrogen spectroscopy and from the electron-proton scattering. The proton radius in muonic hydrogen is measured through the Lamb shift. We will give a full model independent analysis of it within an effective field theory framework, focusing on its hadronic contributions, which are the main source of theoretical uncertainty. We will also review which are the most likely theoretical and experimental sources for this discrepancy and which is the state of this puzzle at the moment.

-  30 April 2015, Christian Gross (Helsinki University) A second Higgs from the Higgs portal

In the Higgs portal framework, the Standard Model Higgs mixes with a singlet scalar, leading to the existence of two states H_1 and H_2, where H_1 is identified with the 125 GeV scalar observed at the LHC. In this talk I will discuss, (i), how the additional scalar can stabilise the otherwise-metastable electroweak vacuum, and (ii), in how far its mass and its mixing angle with H_2 are constraint by current experimental data. I will also show the prospects for observing the decay H_2 -> H_1 H_1 at LHC-13.

-  16 April 2015, Felix Yu (Mainz University) New Physics in WW Scattering

We motivate and discuss the importance of vector boson scattering (VBS) measurements at the LHC and future hadron colliders. We also characterize the measurement in the larger context of on-shell and off-shell Higgs studies and prospects at the LHC. We present a phenomenological study of the various VBS channels, motivating the same-sign WW scattering process as the most promising. We analyze isolating the critical Higgs-related pieces of the WW scattering amplitude and show preliminary prospects for using the same measurement to identify contributions from concrete new physics models.

-  2 April 2015, Takashi Toma (LPT Orsay) Radiative Neutrino Masses and Dark Matter

Although non-zero neutrino masses and existence of dark matter have been confirmed experimentally, both of them are not explained in the standard model. Radiative seesaw mechanism is one of the possibilities which solve these two different issues simultaneously. In some models with radiative neutrino masses, neutrino mass generation and dark matter are correlated since dark matter particle run in the loop for neutrino masses. We discuss and compare this kind of models, and properties of the dark matter particles are also discussed. In particular, Majorana dark matter in the models emits a characteristic gamma-ray as signature of indirect detection of dark matter.

-  19 March 2015, Pradipta Ghosh (Madrid University) Searching evidences of new physics in the light of extended supersymmetric models

Supersymmetric theories with singlets can accommodate light scalar(s), pseudoscalar(s) and neutralino(s) in certain regions of the parameter space. These states, through their presence in the decay cascades of the heavier particles can lead to novel signatures at the LHC. This conclusion is not only limited to supersymmetric particles but also extended for the heavy standard model particles. We emphasise how the presence of these light states produces distinct final states at the LHC. Analyses of these kinds with heavy standard model particles (e.g., W±, Z, Higgs) are viable alternatives to verify the evidence of new physics beyond the standard model when rest of the mass spectrum remains beyond the reach of the LHC. We exemplify our analysis with the μνSSM, where three families of the right-handed neutrino superfields have been used to offer a solution to the μ-problem and at the same time, to house the observed three flavour neutrino data.

-  19 February 2015, Roberto Franceschini (CERN) Energy peaks and future progress on the top quark mass measurement

In this talk I will review recent experimental results on the measurement of top quark mass and their relation to open theoretical issues about the physics of the Standard Model and beyond. With the goal of getting a better understanding of these issues, I will present a class of new top quark mass measurement techniques. The proposed measurement determines the top quark mass from the position of the peak of the energy distribution of the top quark decay products (for instance bottom quark jets or hadrons). Preliminary results on the top quark mass determination from energy distributions computed at Next to Leading Order in QCD will be presented.

-  12 February 2015, Ninetta Saviano (IPPP Durham) Neutrinos in cosmology : current bounds and new physics scenarios

Relic neutrinos play an important role in the evolution of the Universe, having a remarkable impact on the cosmological observables. Notably, Big Bang Nucleosynthesis (BBN), Cosmic Microwave Background (CMB) and Structure Formation (LSS) data represent powerful probes for the neutrino properties. In this talk we show how these cosmological data can be used to bound the absolute scale of neutrino masses and the effective number of neutrino species (N_eff). We also discuss the cosmological impact of sterile neutrinos that would act as a portal towards new physics scenarios. In particular eV sterile neutrinos, suggested by laboratory anomalies, could modify the standard framework requiring large primordial neutrino asymmetries or secret neutrino self-interactions to accommodate these particles with cosmological observations.

-  5 February 2015, Akaki Rusetsky (Bonn University) Finite-volume methods in the analysis of lattice data

It is well known that the resonances can not be identified with an isolated energy level, which is measured in lattice simulations. In order to extract the parameters of resonances on the lattice, one has to relate the energy levels, measured in a finite volume, to the infinite-volume scattering phase shift at the same energy. This method goes under the name of Luescher’s approach. In this talk, using the effective field techniques in a finite volume, we generalize Luescher’s approach to study the matrix elements of the resonances, such as the electromagnetic form factor of the $\Delta$ or the $\Delta N \gamma^*$ transition form factor. An analog of the Luescher-Lellouch formula is derived for the pion photo-production off nucleons. We further apply the similar techniques to study the volume-dependence of the lattice spectrum in the three-particle sector and, in particular, derive an explicit expression for the volume-dependence of a three-particle shallow bound state.

-  29 January 2015, Florian Goertz (CERN) New Physics in the Higgs Sector

The discovery of the Higgs boson opened a unique window to test new physics. In this talk I will first consider prospects to measure the Higgs potential in an effective field theory extension of the Standard Model. I will also address possibilities to gain knowledge about the Yukawa couplings of the lighter quark generations, which is challenging at the LHC. Then, I am going to discuss the impact of the discovery of a light Higgs boson on minimal composite Higgs models and options to mitigate their tension with negative results in searches for light top partners.

-  11 December 2014, Fady Bishara (Cincinnati) Dark matter and flavor

We show that flavor symmetries can lead to dark matter stability without the need to impose additional discrete or continuous symmetries specifically for this purpose. We explore two scenarios. In the first, the metastability of asymmetric dark matter (ADM) derives from the breaking of continuous flavor symmetries. We show that, for ADM that carries nonzero baryon number, the continuous flavor symmetries that generate the flavor structure in the quark sector also imply a looser lower bound on the mass scale of the asymmetric mediators between the dark and visible sectors. We show that the mediators for B = 2 ADM can be of O(TeV) and can thus be searched for at the LHC. In the second scenario we show that flavor triality protects dark matter from decay even with non-MFV flavor breaking. We show that there is a viable region in parameter space where we obtain the correct thermal relic density while satisfying bounds from direct searches for the mediators at the LHC and low energy flavor observables.

-  04 December 2014, Giorgio Arcadi (LPT Orsay) Direct, Indirect and collider signals of Dark Portal scenarios

We will discuss same simple, but rather general scenarios, in which a (fermionic) dark matter interacts with Standard Model fermions through a mediator whose mass is accessible to collider production. Focussing in particular on Z/Z’ mediators, we will show how the constraints from Dark Matter phenomenology, in particular the correct relic abundance and the limits from Direct Detection, determine the nature, axial or vectorial, of the dark matter couplings. We will then discuss the detection prospects of next future experiments in view of these results. We will also investigate whether it is possible to accommodate in these scenarios the recently reported gamma-ray excess from the Galactic Center.

-  27 November 2014, Javier Virto (Siegen) Four-Body contributions to B->Xs\gamma at NLO

Ongoing efforts to reduce the perturbative uncertainty in the B->Xs gamma decay rate have resulted in a theory prediction to NNLO accuracy. However, a few contributions from multi-parton final states which are formally NLO are still unknown. These are parametrically small and included in the estimated error from higher order corrections, but must be computed if one is to claim a complete knowledge of the B->Xs gamma rate to NLO. A major part of these unknown pieces are four-body contributions corresponding to the partonic process $b\to s\bar q q\gamma$. We compute these NLO four-body contributions and confirm the corresponding tree-level LO results. While the NLO contributions arise from tree-level and one-loop Feynman diagrams, the four-body phase-space integrations make the computation non-trivial. The decay rate contains collinear logarithms arising from the mass regularization of collinear divergences. We perform an exhaustive numerical analysis, and find that these contributions are positive and amount to no more than 1% of the total rate in the SM, thus confirming previous estimates of the perturbative uncertainty.

-  20 November 2014 Marco Zaro (Jussieu) W-assisted top asymmetry and polarisation at the LHC

I will present a study about the charge asymmetry of the top quark at the LHC. After introducing the topic and discussing why the measurement of the charge asymmetry at the LHC is quite challenging, I will show how the associated production of a top pair with a W boson can render such a measurement easier. If, on one hand, the extra W boson leads to an important reduction of the total cross-section, on the other hand it naturally selects only the asymmetric production channel (qq initiated) at the LO, leading to a significantly larger prediction of the asymmetry. Furthermore, the extra W boson polarises the quarks, leading to a highly asymmetric production of the top decay products. I will present the expected results for the LHC, and discuss a simple BSM scenario to show how this observable can be sensitive to new physics.

-  6 November 2014 Jose Miguel No (Sussex) Could extra Higgses at the LHC lead to baryogenesis ?

The existence of extra Higgses in Nature could lead to a cosmological first order electroweak (EW) phase transition and explain the origin of the matter-antimatter asymmetry in the Universe. We discuss two possible such scenarios, analyzing the LHC `smoking gun’ signatures of such a phase transition : We first consider a two-Higgs-doublet model, and show that the observation of the decay A0 -> H0 Z at the 14 TeV run of LHC in llbb or llW+W− final states would signal a strong EW phase transition as required by baryogenesis. We then discuss Higgs portal scenarios, where resonant di-Higgs production may constitute a powerful probe of the nature of the phase transition.