Maximizing the Impact of New Physics in $b\rightarrow c \tau \nu$ Anomalies

Understand

We develop a rigorous, semi-analytical method for maximizing any $b\to c\tau\nu$ observable in the full 20-real-dimensional parameter space of the dimension 6 effective Hamiltonian, given some fixed values of $R_{D^{(*)}}$.

• We apply our method to find the maximum allowed values of $F^L_{D^*}$ and $R_{J/\psi}$, two observables which have both come out higher than their SM predictions in recent measurements by the Belle and LHCb collaborations.
• While the measurements still have large error bars, they add to the existing $R_{D^{(*)}}$ anomaly, and it is worthwhile to consider NP explanations.
• It has been shown that none of the existing, minimal models in the literature can explain the observed values of $F^L_{D^*}$ and $R_{J/\psi}$.