Particle decay in expanding Friedmann-Robertson-Walker universes

TL;DR

This paper investigates how particle decay rates are affected by the curvature of expanding universes, showing that gravitational coupling can alter decay processes significantly, which is crucial for accurate early universe cosmology.

Contribution

It provides the first analysis of particle decay in a general power-law universe with arbitrary gravitational coupling, extending beyond minimal or conformal coupling assumptions.

Findings

Decay rates can be strengthened or weakened by gravity depending on coupling.

For certain couplings, decay rates match Minkowskian values across universe types.

Curved spacetime effects are significant for precise cosmological calculations.

Abstract

The lack of energy conservation introduces new particle processes in curved spacetime that are forbidden in flat space. Therefore one has to be very cautious about using the results calculated in Minkowskian space in early universe applications. This is true for particle decay rates in particular, which need to be calculated using quantum field theory in curved spacetime. Previous studies are usually restricted to using minimal or conformal coupling for the decaying particle, while using a more general coupling would give deeper insight into particle decay. This paper presents the results we obtained for a massive particle decaying in a general power-law universe with arbitrary coupling to gravity. We find that depending on the value of the gravitational coupling, the effect of gravitation may either strengthen or weaken the decay. The analysis further reveals that, apart from radiation dominated universe, there are values of the coupling constant for which the decay rate is exactly Minkowskian for all universe types. Because the decay rate may be considerably modified in curved space, these issues need to be considered when doing precise cosmological calculations.