Must cosmological perturbations remain nonadiabatic after multifield inflation?

Even if nonadiabatic perturbations are generated in multifield inflation, the perturbations will become adiabatic if the Universe after inflation enters an era of local thermal equilibrium, with no nonzero conserved quantities, and will remain adiabatic as long as the wavelength is outside the horizon, even when local thermal equilibrium no longer applies. Small initial nonadiabatic perturbations associated with imperfect local thermal equilibrium remain small when baryons are created from out-of-equilibrium decay of massive particles, or when dark matter particles go out of local thermal equilibrium.