  Heavy meson decays with missing energy in the final state offer interesting
avenues to search for light invisible new physics such as dark matter (DM). In
this context, we show that such NP interactions also affect lifetime difference
in neutral meson-antimeson mixing. We consider general dimension-six effective
quark interactions involving a pair of DM particles and calculate their
contributions to lifetime difference in beauty and charm meson systems. We use
the latest data on mixing observables to constrain the relevant effective
operators. We find that lifetime differences provide novel and complementary
flavor constraints compared to those obtained from heavy meson decays.
