Abstract
In this paper, we show that the baryon-to-photon ratio is in general not conserved before decoupling in nonminimally coupled theories of gravity. We use big-bang nucleosynthesis and cosmic microwave background (CMB) limits on the baryon-to-photon ratio to derive new constraints on modified gravity theories with a universal nonminimal coupling between matter and curvature, showing that they rule out a specific class of models previously considered in the literature as a substitute for the dark matter. We also compare these new constraints with the ones obtained from the COBE-FIRAS limits on CMB spectral distortions, highlighting the complementarity between them.
- Received 3 July 2018
DOI:https://doi.org/10.1103/PhysRevD.98.064045
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