New physics searches in $B\to D^{(\ast )}\tau \nu$ decays

I review the current status of measurements involving semi-tauonic $B$ meson decay at the $B$-factories. I briefly discuss the experimental methods and highlight the importance of background contributions especially from poorly understood $D^{\ast \ast }$ in this study. Perhaps this can also shed some light on the discrepancy in the BaBar measurement of ratio of semi-tauonic and semi-leptonic ($e$/$\mu$) modes of $B$ decay from the Standard Model (SM) at 3.2$\sigma$. I will also discuss one of the New Physics (NP) models that could be experimentally sensitive in being distinguished from the Standard Model (SM).