## Journal Club

Seminar Room, Mondays at 14:00

# The Electroweak Vacuum Angle

We reveal a new source of CP-violation in the electroweak sector that is free of any experimental bounds, and we highlight the implications for baryogenesis.
 Subjects: High Energy Physics - Phenomenology (hep-ph) Cite as: arXiv:1402.6340 [hep-ph] (or arXiv:1402.6340v1 [hep-ph] for this version)

Presented by Santiago

# Dressing L_mu - L_tau in Color

We consider a new massive vector-boson Z' that couples to leptons through the L_mu - L_tau current, and to quarks through an arbitrary set of couplings. We show that such a model can be obtained from a renormalizable field theory involving new heavy fermions in an anomaly-free representation. The model is a candidate explanation for the discrepancy observed recently by the LHCb collaboration in angular distributions of the final state particles in the rare decay B \to K* mu^+ mu^-. Interestingly, the new vector-boson contribution to the decay tau \to mu nu_tau \bar nu_mu can also remove a small tension in the measurement of the corresponding branching ratio. Constraints from light flavor meson-mixing restrict the coupling to the up- and down-quarks to be very small and thus direct production of the vector-boson at hadron colliders is strongly suppressed. The most promising ways to test the model is through the measurement of the Z decay to four leptons and through its effect on neutrino trident production of muon pairs. This latter process is a powerful but little-known constraint, which surprisingly rules out explanations of (g-2)_mu based on Z' gauge bosons coupled to muon number, with mass of at least a few GeV.
 Comments: 11 pages, 6 figures Subjects: High Energy Physics - Phenomenology (hep-ph) Cite as: arXiv:1403.1269 [hep-ph] (or arXiv:1403.1269v1 [hep-ph] for this version)

Presented by Santiago

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