## Journal Club

Seminar Room

If you want to propose a paper, you can contact **Supratim Das Bakshi** (*sdb AT ugr.es*)

### Tuesday 29th of March, 2022

# Search for pair-produced vector-like leptons in ≥ 3b + Nτ final states

**The CMS Collaboration**

A search for vector-like leptons (VLLs) is presented in the context of the 4321 model, a UV-complete model with the potential to explain existing B-physics measurements that are in tension with standard model predictions. The analyzed data correspond to an integrated luminosity of 97 fb−1, and were recorded by the CMS detector at the LHC in proton-proton collisions at √s = 13 TeV at the LHC. Final states with ≥ 3 b jets and two third-generation leptons (ττ, τντ, or ντ ντ) are targeted. Expected upper limits are derived on the VLL production cross section in the VLL mass range 500 − 1050 GeV, assuming only electroweak production. At the low end of this mass range, the expected limits are below the expected production cross section, whereas at the high end of the mass range the expected upper limits on the production cross section are several times higher than the expected cross section for electroweak production. A mild excess, consistent with a possible signal, is observed in the data, such that the observed upper limits are approximately double the expected limits. The maximum likelihood fit prefers the presence of signal at the level of 2.8 σ, for a representative VLL mass point of 600 GeV. |

Speaker: **Javi Fuentes**

Links**: **https://cds.cern.ch/record/2803736/files/B2G-21-004-pas.pdf

https://moriond.in2p3.fr/2022/EW/slides/2/2/5_KCormier.pdf

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# Entanglement production in the dynamical Casimir effect at parametric resonance

The particles produced from the vacuum in the dynamical Casimir effect are highly entangled. In order to quantify the correlations generated by the process of vacuum decay induced by moving mirrors, we study the entanglement evolution in the dynamical Casimir effect by computing the time-dependent Rényi and von Neumann entanglement entropy analytically in arbitrary dimensions. We consider the system at parametric resonance, where the effect is enhanced. We find that, in (1+1) dimensions, the entropies grow logarithmically for large times, S_A(tau)~log(tau)/2 while in higher dimensions (n+1) the growth is linear, S_A(t)~ lambda tau where lambda can be identified with the Lyapunov exponent of a classical instability in the system. In (1+1) dimensions, strong interactions among field modes prevent the parametric resonance from manifesting as a Lyapunov instability, leading to a sublinear entropy growth associated with a constant rate of particle production in the resonant mode. Interestingly, the logarithmic growth comes with a pre-factor with 1/2 which cannot occur in time-periodic systems with finitely many degrees of freedom and is thus a special property of bosonic field theories.

Journal reference: | Phys. Rev. D 100, 065022 (2019) |

Related DOI: | https://doi.org/10.1103/PhysRevD.100.065022 |

Speaker: **Javi Olmedo**

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