New physics in $\mathrm{\Delta }{\mathrm{\Gamma }}_d$

We analyze the possibility of having new physics effects in the decay rate difference, $\mathrm{\Delta }{\mathrm{\Gamma }}_d$, 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 $(\bar{d}p)({\bar{p}}^{\mathrm{\prime }}b)$ with $p,p^{\mathrm{\prime }}=u,c$; 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 $\mathrm{\Delta }{\mathrm{\Gamma }}_d$ are not excluded by current experimental data.