Hot scalar radiation setting bounds on the curvature coupling parameter

TL;DR

This paper investigates how the curvature coupling parameter affects the stability of thermodynamic equilibrium for massless scalar radiation near a boundary, establishing bounds that include conformal but exclude minimal coupling.

Contribution

It determines the range of the curvature coupling parameter that allows stable equilibrium, highlighting differences between conformal and minimal coupling in higher dimensions.

Findings

Stable equilibrium requires the curvature coupling parameter to be within a specific range.

The conformal coupling is within this range, while the minimal coupling is not.

The results apply to both massless and massive scalar fields in higher-dimensional spacetimes.

Abstract

This paper addresses the interplay between vacuum and thermal local averages for massless scalar radiation near a plane wall of a large cavity where the Dirichlet boundary condition is assumed to hold. The main result is that stable thermodynamic equilibrium is possible only if the curvature coupling parameter is restricted to a certain range. In more than three spacetime dimensions such a range contains the conformal coupling, but it does not contain the minimal coupling. Since this same range for possible values of the curvature coupling parameter also applies to massive scalar radiation, it may be relevant in settings where arbitrarily coupled scalar fields are present.