A novel determination of the B_c lifetime

To reduce the current theory uncertainties a novel way to determine the $B_c$ lifetime, $\tau_{B_c}$, is proposed. Taking the difference of the $B_c$, and $B$ and $D$ meson decay rates eliminates the leading contributions from the calculation, which exhibit large scale and scheme dependence. The uncertainties in the proposed determination of $\tau_{B_c}$ are analyzed and improvements are proposed. The method predicts a value of $\tau_{B_c}$ in tension with the experimental determination. Several explanations are considered, including underestimation of uncertainties, duality violation and new physics. We discuss quantitative evidence that our method is vitiated by duality violation in the large mass OPE used to calculate nonleptonic decay rates of $B$ and $D$ mesons.