Stealth metastable state of scalar-tensor thermodynamics

TL;DR

This paper explores the thermodynamic properties of scalar-tensor gravity, revealing a metastable stealth state in Brans-Dicke theory that is unstable under tensor perturbations, using a gauge-invariant stability analysis.

Contribution

It introduces a novel stability analysis of scalar-tensor thermodynamics, identifying a metastable stealth solution analogous to a non-equilibrium state.

Findings

Stealth solution in Brans-Dicke gravity exhibits metastability.

Tensor perturbations destabilize the stealth state.

Gauge-invariant formalism effectively analyzes stability in modified gravity.

Abstract

We investigate a puzzle in the recent thermodynamics of scalar-tensor gravity, in which general relativity is a zero-temperature state of equilibrium and scalar-tensor gravity is the non-equilibrium configuration of an effective dissipative fluid. A stealth solution of Brans-Dicke gravity with constant positive temperature is shown to be analogous to a metastable state for the effective fluid and to suffer from an instability. The stability analysis employs a version of the Bardeen-Ellis-Bruni-Hwang gauge-invariant formalism for cosmological perturbations adapted to modified gravity. The metastable state is destroyed by tensor perturbations.