New physics in $\Delta \Gamma_d$

We analyze the possibility of having new physics effects in the decay rate difference, $\Delta \Gamma_d$, of neutral $B_d$ mesons. Three different sources of enhancement are considered, CKM unitarity violations, beyond standard model effects in the tree-level dimension six operators $(\bar{d}p)(\bar{p}'b)$ with $p,p'=u,c$; and large enhancements of the almost unconstrained operators $(\bar{d}b)(\bar{\tau}\tau)$. We find that deviations of several hundred per cent from the standard model prediction of $\Delta \Gamma_d$ are not excluded by current experimental data.