  In this article, we have predicted the standard model (SM) values of the
asymmetric and angular observables in $B\to D^{(\ast)}\tau\nu_{\tau}$ decays,
using the results of the new up-to-date analysis in $B\to
D^{(*)}\ell\nu_{\ell}$. We have also revisited the SM prediction of the
inclusive ratio $\mathcal{R}_{X_c}$, and have given its values in different
schemes of the charm quark mass. This is the first analysis which includes all
the known corrections in the SM. In addition, we have analysed the $b\to
c\tau\nu_\tau$ decay modes in a model-independent framework of effective field
theory beyond the standard model. Considering all the possible combinations of
the effective operators in $b \to c \tau\nu_{\tau}$ decays and using the Akaike
Information Criterion, we find out the scenarios which can best explain the
available data on these channels. In the selected scenarios, best-fit values
and correlations of the new parameters are extracted. Using these results,
predictions are made on various observables in the exclusive and inclusive
semitaunic $b \to c $ decays. The graphical correlations between these
observables are shown, which are found to be useful in discriminating various
new physics scenarios.
