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

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.