Helicity amplitudes in the $\bar{B} \to D^{*} \bar{\nu}_\tau \tau$ decay with $V-A$ breaking in the quark sector

TL;DR

This paper analyzes the helicity amplitudes in the $ar{B} o D^{*} ar{ u}_ au au$ decay, comparing standard model predictions with models that break $V-A$ symmetry in the quark sector, focusing on the sensitivity of transverse contributions to new physics.

Contribution

It evaluates helicity amplitudes in $ar{B} o D^{*} ar{ u}_ au au$ decay for models with $V-A$ breaking, highlighting the sensitivity of transverse components to such effects.

Findings

Transverse contributions are more sensitive to $V-A$ breaking than longitudinal.

Differences in $M=-1$ and $M=+1$ amplitudes reveal potential new physics effects.

Standard model predictions are compared with models having different $ ext{V-A}$ structures.

Abstract

In view of the recent measurement of the $F_L^{D^*}$ magnitude in the $\bar{B} \to D^{*} \bar{\nu}_\tau \tau$ reaction we evaluate this magnitude within the standard model and for a family of models with the $\gamma^\mu -\alpha\gamma^\mu \gamma_5$ current structure for the quarks for different values of $\alpha$. At the same time we evaluate also the transverse contributions, $M=-1$, $M=+1$, and find that the difference between the $M=-1$ and $M=+1$ contributions is far more sensitive to changes in $\alpha$ than the longitudinal component.