TCP conservation in cosmology

We investigate decay processes in an expanding universe. The Born approximation conforms to one's expectations: emission of particles with energy conservation and subsequent cooling down. Interference graphs containing CP-violating effects are then investigated with an eye to discovering a violation of TCP. Such effects are found to be much smaller than what one might have thought, even for very rapid expansion and in the particular cosmology described by an asymptotic de Sitter space, TCP violations vanish identically.