Lepton-flavor universality violation in \(R_{D^{(*)}}\) and \(R_K\) from warped space

Abstract

Some anomalies in the processes \(b\to s\ell\ell\) (\(\ell=\mu,e\)) and \(b\to c \ell\bar\nu_\ell\) (\(\ell=\tau,\mu,e\)), in particular in the observables \(R_{D^{(*)}}\) and \(R_K\), have been found by the BaBar, LHCb and Belle Collaborations leading to a possible lepton flavor universality violation. If these anomalies were confirmed they would inevitably lead to physics beyond the Standard Model. In this paper we provide an explanation of the present anomalies in an extra dimensional theory, solving the naturalness problem of the Standard Model by means of a warped metric with a strong conformality violation near the infra-red brane. All anomalies can be accommodated provided that the left-handed bottom quark and tau lepton have a strong, and the left-handed muon lepton a mild, degree of compositeness in the dual theory. The theory is consistent with all electroweak and flavor observables, and with all direct searches of Kaluza-Klein electroweak gauge bosons and gluons. The fermion spectrum, and fermion mixing angles, can be reproduced by mostly elementary right-handed bottom quarks, and tau and muon leptons. In particular the smoking gun for the \(R_{D^{(*)}}\) anomaly in our model should be a branching ratio, larger than the Standard Model prediction, for the process \(\bar B\to \bar K\tau\tau\), although present bounds still leave a wide room in the parameter space.