Unparticle effects on $B\to D^{(*)}\tau\nu$

Abstract

We examine the possible unparticle effects on $R(D^{(*)})$ associated with $B\to D^{(*)}\tau\nu$ decays by minimum-$\chi^2$ fitting. Recent measurements from Belle and LHCb are included in this analysis. While it is true that the new experimental results of $R(D^{(*)})$ get closer to the standard model predictions, there are still rooms for new physics and unparticles are also one possibility. Our best-fit values are $R(D)=0.456$ and $R(D^*)=0.270$, which are still far from the standard model values by more than ($R(D)$) or almost ($R(D^*)$) $2\sigma$. We also find that the unparticle effects are quite safe to render the branching ratio ${\rm Br}(B_c\to\tau\nu)$ less than 10\%.