Lepton universality violation and right-handed currents in $b \to c \tau \nu$

Understand

We consider the recent LHCb result for $B_c\to J/\psi \tau \nu$ in conjunction with the existing anomalies in $R(D)$ and $R(D^\star)$ within the framework of a right-handed current with enhanced couplings to the third generation.

• The model predicts a linear relation between the observables and their SM values in terms of two combinations of parameters.
• The strong constraints from $b\to s \gamma$ on $W-W^\prime$ mixing effectively remove one of the combinations of parameters resulting in an approximate proportionality between all three observables and their SM values.
• To accommodate the current averages for $R(D)$ and $R(D^\star)$, the $W^\prime$ mass should be near 1 TeV, and possibly accessible to direct searches at the LHC.