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

Abstract

We examine the possible unparticle effects on $R(D^{(\ast )})$ associated with $B\to D^{(\ast )}\tau \nu$ 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 $R(D^{(\ast )})$ 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 $R(D^{\ast })=0.270$, which are still far from the standard model values by more than ($R(D)$) or almost ($R(D^{\ast })$) $2\sigma$. We also find that the unparticle effects are quite safe to render the branching ratio $\mathrm{Br}(B_c\to \tau \nu )$ less than 10\%.

Comments: 11 pages, 4 figures