Thermodynamics of scalartensor gravity
Abstract
Previously, the Einstein equation has been described as an equation of state, general relativity as the equilibrium state of gravity, and $f({\cal R})$ gravity as a nonequilibrium one. We apply Eckart's first order thermodynamics to the effective dissipative fluid describing scalartensor gravity. Surprisingly, we obtain simple expressions for the effective heat flux, "temperature of gravity", shear and bulk viscosity, and entropy density, plus a generalized Fourier law in a consistent Eckart thermodynamical picture. Welldefined notions of temperature and approach to equilibrium, missing in the current thermodynamics of spacetime scenarios, naturally emerge.
 Publication:

arXiv eprints
 Pub Date:
 March 2021
 arXiv:
 arXiv:2103.05389
 Bibcode:
 2021arXiv210305389F
 Keywords:

 General Relativity and Quantum Cosmology;
 High Energy Physics  Theory
 EPrint:
 5 pages. Corrected Eq. (26) describing the approach to equilibrium and one typographical error. Matches Letter to appear in Physical Review D