Resolution of $R_D$/$R_{D^{\ast }}$ puzzle

Abstract

One of the exciting results in flavor physics in recent times is the $R_D$/$R_{D^{\ast }}$ puzzle. The measurements of these flavor ratios performed by the B-factory experiments, BaBar and Belle, and the LHCb experiment are about $4\sigma$ away from the Standard Model expectation. These measurements indicate that the mechanism of $b\to c\tau \bar{\nu }$ decay is not identical to that of $b\to c(\mu /e)\bar{\nu }$. This charge lepton universality violation is particularly intriguing because these decays occur at tree level in the Standard Model. In particular, we expect a moderately large new physics contribution to $b\to c\tau \bar{\nu }$. The different types of new physics amplitudes, which can explain the $R_D$/$R_{D^{\ast }}$ puzzle, have been identified previously. In this letter, we show that the polarization fractions of $\tau$ and $D^{\ast }$ and the angular asymmetries $A_{FB}$ and $A_{LT}$ in $B\to D^{\ast }\tau \bar{\nu }$ decay have the capability to uniquely identify the Lorentz structure of the new physics. A measurement of these four observables will lead to such an identification.

6 pages, 2 figures (Accepted for publication in Physics Letters B)

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• On lepton flavour universality in semileptonic $B_c\to {\eta }_c,J/\psi$ decays
• Asymmetry Observables and the Origin of $R_{D^{(\ast )}}$ Anomalies
• $b\to c\tau \nu$ Transitions in the Standard Model Effective Field Theory
• Solutions to $R_D$-$R_{D^{\ast }}$ in light of Belle 2019 data
• R-parity violating solutions to the $R_{D^{(\ast )}}$ anomaly and their GUT-scale unifications
• Maximizing the Impact of New Physics in $b\to c\tau \nu$ Anomalies
• On the Minimal Flavor Violating Leptoquark Explanation of the $R_{D^{(\ast )}}$ Anomaly
• A comprehensive study on the semileptonic decay of heavy flavor mesons
• Common explanation to the $R_{K^{(\ast )}}$, $R_{D^{(\ast )}}$ and ${\epsilon }^{\prime }/\epsilon$ anomalies in a 3HDM+${\nu }_R$ and connections to neutrino physics
• CP Violation in ${\bar{B}}^0\to D^{\ast +}{\mu }^{-}{\bar{\nu }}_{\mu }$
• A Measurable Angular Distribution for $\bar{B}\to D^{\ast }{\tau }^{-}{\bar{\nu }}_{\tau }$ Decays
• Lepton Flavor Universality tests through angular observables of $\overline{B}\to D^{(\ast )}\ell \overline{\nu }$ decay modes
• Probing effects of new physics in ${\Lambda }_b^0\to {\Lambda }_c^{+}{\mu }^{-}{\bar{\nu }}_{\mu }$ decays
• Implication of $R_{D^{(\ast )}}$ anomalies on semileptonic decays of ${\Sigma }_b$ and ${\Omega }_b$ baryons
• Signatures of complex new physics in $b\to c\tau \bar{\nu }$ transitions
• New physics effects in purely leptonic $B_s^{\ast }$ decays
• Implication of $b\to c\tau \nu$ flavor anomalies on $B_s\to D_s^{\ast }\tau \nu$ decay observables
• New physics footprints in the angular distribution of $B_s\to D_s^{\ast }(\to D_s\gamma ,D_s\pi )\tau \nu$ decays
• A unique discrimination between new physics scenarios in $b\to s{\mu }^{+}{\mu }^{-}$ anomalies
• Effects of nonstandard interaction on temporal and spatial correlations in neutrino oscillations
• Impact of $b\to c$ measurements on ${\Lambda }_b\to p\tau \bar{\nu }$ decay in $U_1$ leptoquark model
• Flavor signatures of complex anomalous $tcZ$ couplings
• New Physics solutions for $b\to c\tau \bar{\nu }$ anomalies after Moriond 2019
• Resolving $R_D$ and $R_{D^{\ast }}$ anomalies
• $B_s^{\ast }\to l^{+}{l}^{-}$ decays in light of recent $B$ anomalies