$R_{D^{(\ast)}}$ in custodial warped space

TL;DR

This paper presents a warped space model with custodial symmetry that explains B-meson decay anomalies involving tau and muon/electron ratios, while also addressing the hierarchy problem and LEP data consistency.

Contribution

It provides a UV-complete warped space model with custodial symmetry that simultaneously explains $R_{D^{(*)}}$, $R_{K^{(*)}}$ anomalies, and predicts an $A^b_{FB}$ deviation consistent with LEP.

Findings

Model explains $R_{D^{(*)}}$ anomaly.

Model addresses $R_{K^{(*)}}$ anomalies.

Predicts an $A^b_{FB}$ deviation compatible with LEP.

Abstract

Flavor physics experiments allow to probe the accuracy of the Standard Model (SM) description at low energies, and are sensitive to new heavy gauge bosons that couple to quarks and leptons in a relevant way. The apparent anomaly in the ratios of the decay of $B$-mesons into $D$-mesons and different lepton flavors, $R_{D^{(\ast)}} = \mathcal B(B \to D^{(\ast)} \tau \nu)/ \mathcal B(B \to D^{(\ast)} \ell \nu )$ is particularly intriguing, since these decay processes occur at tree-level in the SM. Recently, it has been suggested that this anomaly may be explained by new gauge bosons coupled to right-handed currents of quarks and leptons, involving light right-handed neutrinos. In this work we present a well-motivated ultraviolet complete realization of this idea, embedding the SM in a warped space with an $SU(2)_L \otimes SU(2)_R \otimes U(1)_{B-L}$ bulk gauge symmetry. Besides providing a solution to the hierarchy problem, we show that this model, which has an explicit custodial symmetry, can explain the $R_{D^{(\ast)}}$ anomaly and at the same time allow for a solution to the $R_{K^{(\ast)}}$ anomalies, related to the decay of $B$-mesons into $K$-mesons and leptons, $R_{K^{(*)}} = \mathcal B(B\to K^{(*)} \mu \mu)/ \mathcal B(B \to K^{(*)} e e)$. In addition, a model prediction is an anomalous value of the forward-backward asymmetry $A^b_{FB}$, driven by the $Z\bar b_R b_R$ coupling, in agreement with LEP data.