  Deviations from the standard model prediction have been observed not only in
$b \to c$ charged current interactions but also in $b \to s$ flavor changing
neutral current interactions. In particular, the deviation observed in the
measured ratio of branching fractions $R_D = \mathcal B(B \to
D\tau\nu)/\mathcal B(B \to D\,l\,\nu)$ and $R_{D^{\ast}} =\mathcal B(B \to
D^{\ast}\tau\nu)/\mathcal B(B \to D^{\ast}\,l\,\nu)$, where $l = (e,\,\mu)$, is
more pronounced and the combined excess currently stands at $3.9\sigma$ level.
If it persists and confirmed by future experiments, it would be a definite hint
of new physics. In this context, we consider $B_c \to \eta_c\,l\,\nu$ and $B_c
\to J/\Psi\,l\,\nu$ decays mediated via $b \to c\,l\,\nu$ charged current
interactions and employ the most general effective Lagrangian in the presence
of new physics to give prediction on various observables such as ratio of
branching ratio, tau polarization fraction, and forward backward asymmetry for
these decay modes.
