The $V_{cb}$ puzzle: an update

Abstract

We discuss the impact of the recent untagged analysis of $B^0\to D^{\ast }l{\bar{\nu }}_l$ decays by the Belle Collaboration on the extraction of the CKM element $|V_{cb}|$ and provide updated SM predictions for the $b\to c\tau \nu$ observables $R(D^{\ast })$, $P_{\tau }$, and $F_L^{D^{\ast }}$. The value of $|V_{cb}|$ that we find is about $2\sigma$ from the one from inclusive semileptonic $B$ decays, and is very sensitive to the slope of the form factor at zero recoil which should soon become available from lattice calculations.

Comments: 7 pages, 4 figures. Minor changes, 2 additional figures