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Must Cosmological Perturbations Remain Non-Adiabatic After Multi-Field Inflation?

Steven Weinberg
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Abstract

Even if non-adiabatic perturbations are generated in multi-field inflation, the perturbations will become adiabatic if the universe after inflation enters an era of local thermal equilibrium, with no non-zero 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 non-adiabatic 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.

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Steven Weinberg. 2004-07-20. Must Cosmological Perturbations Remain Non-Adiabatic After Multi-Field Inflation?. https://doi.org/10.1103/physrevd.70.083522

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