Abstract
Motivated by the recent LHCb announcement of a 3.1σ violation of lepton- flavor universality in the ratio RK = 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 → ctau 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 U1 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 Bs- {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(*) nu overline{nu} ), and finally an updated analysis of collider bounds on the leptoquark mass and couplings.
Highlights
Motivated by the recent LHCb announcement of a 3.1σ violation of leptonflavor universality in the ratio RK = Γ(B → Kμ+μ−)/Γ(B → Ke+e−), we present an updated, comprehensive analysis of the flavor anomalies seen in both neutral-current (b → s + −) and charged-current (b → cτ ν) decays of B mesons
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 broken U(2)5 flavor symmetry
As we shall show in this paper, combining all the b → s + − observables in a very conservative way, the significance of the New Physics (NP) hypothesis formulated in 2014–2015 of a purely left-handed LFU-violating contact interaction has reached a significance of 4.6σ
Summary
Attempts to explain one or both sets of anomalies have stimulated an intense theoretical activity, which ranges from pure Effective Field Theory (EFT) approaches to the formulation of motivated ultraviolet (UV) completions of the SM In the latter category, models containing a TeV-scale vector leptoquark, U1 ∼ (3, 1, 2/3), as the main mediator are appealing. It emerged more clearly that the flavor structure of the new interaction is quite constrained in the case of combined explanations, and naturally follows the hypothesis of a minimally broken U(2) flavor symmetry [30, 36] — a hypothesis formulated well before the anomalies appeared [39], which links them to the origin of the hierarchies observed in the SM Yukawa couplings. Its rich field content and the three-scale structure behind the origin of the flavor hierarchies finds a simple interpretation in terms of a compact extra dimension of spacetime, with the flavor index of the four-dimensional fields being in one-to-one correspondence with the location of four-dimensional branes along the fifth dimension
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
