$\bar{B}\to D^{(\ast )}\tau \bar{\nu }$ excesses in ALRSM constrained from $B$, $D$ decays and $D^0-{\bar{D}}^0$ mixing

Abstract

Recent experimental results from the LHCb, BaBar and Belle collaborations on the semitauonic decays of $B$ meson, $\bar{B}\to D^{(\ast )}\tau \bar{\nu }$, showing a significant deviation from the Standard Model (SM), hint towards a new physics scenario beyond the SM. In this work, we show that these enhanced decay rates can be explained within the framework of $E_6$ motivated Alternative Left-Right Symmetric Model (ALRSM), which has been successful in explaining the recent CMS excesses and has the feature of accommodating high scale leptogenesis. The R-parity conserving couplings in ALRSM can contribute universally to both $\bar{B}\to D\tau \bar{\nu }$ and $\bar{B}\to D^{(\ast )}\tau \bar{\nu }$ via the exchange of scalar leptoquarks. We study the leptonic decays $D_s^{+}\to {\tau }^{+}\bar{\nu }$, $B^{+}\to {\tau }^{+}\bar{\nu }$, $D^{+}\to {\tau }^{+}\bar{\nu }$ and $D^0$-${\bar{D}}^0$ mixing to constrain the couplings involved in explaining the enhanced $B$ decay rates and we find that ALRSM can explain the current experimental data on $\mathcal{R}(D^{(\ast )})$ quite well while satisfying these constraints.

Comments: 10 pages, 10 figures, minor refinements, all results unchanged, new references added