In extended models of gravity, a nonminimal coupling to matter has been assumed to lead to irreversible particle creation. In this paper, we challenge this assumption. We argue that a nonminimal coupling of the matter and gravitational sectors results in a change in particle momentum on a cosmological time scale, irrespective of particle creation or decay. We further argue that particle creation or decay associated with a nonminimal coupling to gravity could only happen as a result of significant deviations from a homogeneous Friedmann-Lemaítre-Robertson-Walker geometry on microscopic scales and provide a phenomenological description of the impact of particle creation or decay on the cosmological evolution of the density of the matter fields.

• Received 18 January 2019

DOI:https://doi.org/10.1103/PhysRevD.99.064027