Aspects of axion F(R) gravity

¹ ICREA - Passeig Luis Companys, 23, 08010 Barcelona, Spain
² Institute of Space Sciences (IEEC- CSIC) - C. Can Magrans s/n, 08193 Barcelona, Spain
³ Department of Physics, Aristotle University of Thessaloniki - Thessaloniki 54124, Greece
⁴ Laboratory for Theoretical Cosmology, Tomsk State University of Control Systems and Radioelectronics (TUSUR) 634050 Tomsk, Russia
⁵ Tomsk State Pedagogical University - 634061 Tomsk, Russia

Received: 20 February 2020
Accepted: 6 March 2020

Abstract

We provide a compact review on recent developments on axion F(R) gravity. The axion field is a string-theory–originated theoretical particle that is a perfect candidate for low-mass particle dark matter. In this review we present how a viable inflationary phenomenology and a viable late-time evolution can be described by an axion F(R) gravity theory, in which the F(R) gravity part can drive in a geometric way the inflationary and the late-time era, and the axion field behaves as dark matter, with its energy density behaving as a function of the scale factor as . We also briefly discuss the effect of a non-trivial axion Chern-Simons coupling on the inflationary phenomenology of the R² model. Finally, we briefly discuss the effects of a non-minimal coupling of the axion field with the curvature on neutron stars, and also the propagation of gravity waves in Chern-Simons axion gravity.