In these mini-proceedings we review the results of the workshop `Impact of $B\to\mu^+\mu^-$ on New Physics Searches' that took place at the Paul Scherrer Institute (PSI) on the 18th-19th December 2017.

I present a few model building lessons for high-p T searches at the LHC when addressing recently reported hints on lepton flavour universality violation in semi-tauonic and rare B - meson decays.

We provide an ultraviolet (UV) complete model for the R(D(∗)) anomalies, in which the additional contribution to semi-tauonic b → c transitions arises from decay to a right-handed sterile neutrino via exchange of a TeV-scale SU(2)L singlet W ′. The model is based on an extension of the Standard Model (SM) hypercharge group, U(1)Y , to the SU(2)V ×U(1)′ gauge group, containing several pairs of heavy vector-like fermions. We present a comprehensive phenomenological survey of the model, ranging from the lowenergy flavor physics, direct searches at the LHC, to neutrino physics and cosmology. We show that, while the W ′ and Z ′-induced constraints are important, it is possible to find parameter space naturally consistent with all the available data. The sterile neutrino sector also offers rich phenomenology, including possibilities for measurable dark radiation, gamma ray signals, and displaced decays at colliders. ar X iv :1 80 4. 04 64 2v 1 [ he pph ] 1 2 A pr 2 01 8

Admir Greljo, Jorge Martin Camalich, 2, 3 and José David Ruiz-Álvarez Theoretical Physics Department, CERN, 1 Esplanade des Particules, 1211 Geneva 23, Switzerland Instituto de Astrof́ısica de Canarias, C/ Vı́a Láctea, s/n E38205 La Laguna, Tenerife, Spain Universidad de La Laguna, Departamento de Astrof́ısica, La Laguna, Tenerife, Spain Instituto de F́ısica, Universidad de Antioquia, A.A. 1226, Medelĺın, Colombia We investigate the crossing-symmetry relation between b→ cτ−ν̄ decay and bc̄→ τ−ν̄ scattering to derive direct correlations of New Physics in semi-tauonic B-meson decays and the mono-tau signature at the LHC (pp→ τhX + MET). Using an exhaustive set of effective operators and heavy mediators we find that the current ATLAS and CMS data constrain scenarios addressing anomalies in B-decays. Pure tensor solutions, completed by leptoquark, and right-handed solutions, completed by W ′ R or leptoquark, are challenged by our analysis. Furthermore, the sensitivity that will be achieved in the high-luminosity phase of the LHC will probe all the possible scenarios that explain the anomalies. Finally, we note that the LHC is also competitive in the b → u transitions and bounds in some cases are currently better than those from B decays.

LHCb experiment at CERN has recently reported a set of measurements on lepton flavour universality in $b \to s$ transitions showing a departure from the Standard Model predictions. I will review the main ideas recently put forward to make sense out of these intriguing hints. Focusing on the new physics explanation, I will discuss the correlated signals expected in other low- and high-energy observables, that could help clarify the mysterious anomalies.