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

TL;DR

This paper investigates complex new physics contributions to $b\to c\tau\bar{\nu}$ transitions, fitting data to identify solutions, and explores how asymmetries can distinguish these solutions and reveal CP violation.

Contribution

It performs a global fit with complex Wilson coefficients to current data and analyzes CP asymmetries to differentiate new physics scenarios.

Findings

Multiple solutions depend on $Br(B_c\rightarrow \tau\bar{\nu})$ limits.

Forward-backward asymmetries can distinguish solutions.

CP asymmetries can be enhanced up to 2-3% in certain cases.

Abstract

The anomalies in the measurements of $R_D$ and $R_{D^*}$ 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 $b\rightarrow c\tau\bar{\nu}$ data. We find that the number of allowed solutions depend on the choice of the upper limit on $Br(B_c\rightarrow \tau\bar{\nu})$. We find that the forward-backward asymmetries in $B\rightarrow (D, D^*)\tau\bar{\nu}$ decays have the capability to distinguish between different solutions. Further we calculate the maximum values of CP violating triple product asymmetries in $B\to D^*\tau\bar{\nu}$ 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.