Magic Monday Journal Club

13th January 2014

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Thank you to all of you to have been present in a such crowded MMJC!! And thank you for the hospitality of Ecole Polytechnique and the organizing help of Emilian Dudas. In this Journal Club we had a mini-seminar of Christoffer Petersson («the killer») about multiphoton and multiplepton signals from SUSY models at LHC. We include his seminar here. HAve a nice reading!

Multilepton and multiphoton signatures of supersymmetry at the LHC

by Christoffer Petersson

In the first part of the talk, based on arXiv:1310.0018, I discussed the possibility of explaining a small excess of multilepton events recently observed by the CMS collaboration by means of a simplified model of gauge mediated supersymmetry breaking (GMSB). Not only is this model able to explain the excess (without being excluded by any other search), but it also gives rise to signatures which are currently not being searched for at the LHC. In order to completely probe this model I proposed an LHC search in the final state with 2 hadronically decaying taus+2 (or 3) leptons+MET. In the second part of the talk, based on arXiv:1312.1698, I discussed how the standard phenomenology of GMSB can be significantly modified by the non-minimal assumption that supersymmetry is broken in more than one hidden sector. Multiple hidden sectors give rise to light neutral fermions called pseudo-goldstini and due to the extra decay steps they give rise to, where soft photons are emitted, these models give rise to multiphoton plus missing energy signatures. In order to probe these models I proposed two LHC searches. The first one is a fully inclusive search in the final state with at least 3 photons+MET, which would be sensitive to any production mode, and second one in the final state with 2 leptons+(at least) 2 photons+MET, optimized for slepton pair production.   

Key slides in pdf file: Pages 21 and 27 for the first part and pages 43 and 45 for the second part. You can find a pdf version of the talk here.

Higgs Couplings and Electroweak Phase Transition

by A. Katz and M. Perelstein

In the Standard Model the  transition in the early universe from the phase with zero Higgs vev to the phase with a broken electroweak symmetry is believed to be smooth. New physics is needed to modify the thermal Higgs potential such that the phase transision is strongly first order.  The paper studies the connection between the new physics leading to a strongly first-order electroweak phase transition and modifications of the  Higgs couplings that can be measured at the LHC and future e+e- colliders. It argues that,  if the

new physics carries a color charge, these modifications should be observable at the LHC, while in other cases the modifications should be observable at the e+e- colliders. This observation provides some good motivation for precise measurements of the Higgs

couplings, as a means to understand the early universe.

Out-of-equilibrium Baryogenesis and SuperWIMP Dark Matter

by G. Arcadi and L. Covi (presented by G. Arcadi)

Our paper proposes a simple mechanism for connecting baryogenesis and Dark Matter production through the decay of a same mother particle. The baryon and Dark matter density are thus contemporary produced by the out-of-equilibrium decay of a particle. Their ratio results to be independent on the initial density of the mother particle (cfr. expressions (1), (3) and (4)). This mechanism can be embedded in generic particle physics frameworks but works particularly well in Supersymmetric theories with gravitino Dark Matter. We provide two examples of realizations. In the first the decaying field is a TeV scale Bino in RPV-MSSM while in the second the mechanism is embedded in a leptogenesis framework within an extension of a RPC-MSSM with three right-handed neutrinos (snuetrinos) which play the role of mother particles. The outcome for these specific realizations is summarized in figures 2 and 3.


What if lambda_hhh neq 3 mh2/v ?

by A. Efrati and Y. Nir

In this paper, the authors are interested in treating specific extensions of the SM and check their predictions to the self trilinear coupling of the Higgs. Especially, comparing deviation from trilinear coiupling to the one induced to the vectorial coupling, the y can predict for each model the ratio expected in the next run of the LHC. Interesting paper to be introduced on the subject.  You can find an annoted version of the paper here.

Probing Light Nonthermal Dark Matter at the LHC

by V.  B. Dutta1 ,  Y. Gao1 and T. Kamon1

This paper investigates the collider phenomenolgy of a minimal nonthermal dark matter model with a 1-GeV dark matter candidate, which naturally explain baryongensis. Since the light dark matter is not parity-protected, it can be singly produced at the LHC. This leads to large missing energy associated with an energetic jet whose transverse momentum distribution is featured by a Jacobian-like shape. The monojet, dijet, paired dijet and 2 jets + missing energy channels are studied. Currently existing data at Tevatron and LHC offer significant bounds on their model.

Sur la dynamique de l’électron

by H. Poincare


In this article, published 2 weeks before the Einstein one, you can see that the «Lorentz transformation» (which were in fact first found by Poincare) exhibiting a group structure was for the first time printed in this notes of Académie des Science in 1905. This paper was forgotten as another published version appeared in July 1905 in an Italian proceeding of  a mathematical conference he did in Sicilia. The aticle is clear and even propose the basis of general relativity. A nice reading I encourage you to read before sleeping. Or even after!!! You can find an annoted version of the paper here.