Signatures of complex new physics in $b\to c\tau \bar{\nu }$ transitions

Abstract

The anomalies in the measurements of $R_D$ and $R_{D^{\ast }}$ continue to provide motivation for physics beyond the Standard Model. In this work, we assume the new physics Wilson coefficients to be complex and find their values by doing a global fit to the present $b\to c\tau \bar{\nu }$ data. We find that the number of allowed solutions depend on the choice of the upper limit on $Br(B_c\to \tau \bar{\nu })$. We find that the forward-backward asymmetries in $B\to (D,D^{\ast })\tau \bar{\nu }$ decays have the capability to distinguish between different solutions. Further we calculate the maximum values of CP violating triple product asymmetries in $B\to D^{\ast }\tau \bar{\nu }$ decay allowed the current data. We observe that only one of the three CP asymmetries can be enhanced up to a maximum value of $\sim 2-3\%$ whereas the other asymmetries remain smaller.

Comments: 18 pages, 5 figures, Accepted for publication in Nucl. Phys. B