Reading the footprints of the B-meson flavor anomalies

Abstract

Abstract Motivated by the recent LHCb announcement of a 3.1σ violation of lepton- flavor universality in the ratio R K = Γ(B → Kμ + μ − )/Γ(B → Ke + e − ), we present an updated, comprehensive analysis of the flavor anomalies seen in both neutral-current (b → sℓ + ℓ − ) and charged-current (b → cτ ν ¯ $$ c\tau \overline{\nu} $$ ) decays of B mesons. Our study starts from a model-independent effective field-theory approach and then considers both a simplified model and a UV-complete extension of the Standard Model featuring a vector leptoquark U 1 as the main mediator of the anomalies. We show that the new LHCb data corroborate the emerging pattern of a new, predominantly left-handed, semileptonic current-current interaction with a flavor structure respecting a (minimally) broken U(2)5 flavor symmetry. New aspects of our analysis include a combined analysis of the semileptonic operators involving tau leptons, including in particular the important constraint from B s - B ¯ s $$ {\overline{B}}_s $$ mixing, a systematic study of the effects of right-handed leptoquark couplings and of deviations from minimal flavor-symmetry breaking, a detailed analysis of various rare B-decay modes which would provide smoking-gun signatures of this non-standard framework (LFV decays, di-tau modes, and B → K (*) ν ν ¯ $$ \nu \overline{\nu} $$ ), and finally an updated analysis of collider bounds on the leptoquark mass and couplings.

Keywords

• Beyond Standard Model
• Heavy Quark Physics