Effects of Kaluza-Klein Neutrinos on $R_D$ and $R_{D^{\ast }}$

Abstract

Recent measurements of $R_D$ and $R_{D^{\ast }}$ by the LHCb collaboration show deviations from their respective Standard Model values. These semileptonic $B$ meson decays, associated with $b\to c\tau \bar{\nu }$ transition, are pointing toward new physics beyond the Standard Model via leptonic flavor universality violation. In this paper, we show that such anomaly can be resolved by the cummulative Kaluza-Klein (KK) modes of singlet right-handed neutrino which propagates in the large extra dimensional space. We found that the number of extra dimension should be 2 to explain $R_D$ and $R_{D^{\ast }}$. We show that both $R_D$ and $R_{D^{\ast }}$ constraint the energy scale $M_F$ of this extra dimension which are compatible with the limits from lepton flavor violating tau decays. In contrast, our findings are in tension with the limits coming from the neutrino experiments which set the most stringent lower bound on $M_F$. The future measurements of $R_{D^{(\ast )}}^{exp}$ with reduced uncertainties will exclude this extra dimensional model with right-handed neutrino propagating in the bulk, if the central values stay.

Comments: 15 pages, 4 figures