Structural Implications of the Chameleon Mechanism on White Dwarfs

TL;DR

This paper investigates how the chameleon mechanism affects white dwarf structures, showing it reduces their radii and masses, accelerates cooling, and provides parametric formulas for future studies in scalar-tensor theories.

Contribution

It introduces a novel analysis of the chameleon mechanism's impact on white dwarfs, including a new similarity relation and parametric expressions for scalar-tensor models.

Findings

Chameleon field adopts a thick-shell configuration in white dwarfs.

The mechanism reduces white dwarf radii and masses compared to Newtonian predictions.

It accelerates white dwarf cooling by lowering their specific heat.

Abstract

We study the impact of the chameleon mechanism on the structure of white dwarfs. Using a shooting method of our design, we solve the corresponding scalar-tensor equilibrium equations for a Chandrasekhar equation of state, exploring various energy scales and couplings of the chameleon field to matter. For the considered parameter ranges, we find the chameleon field to be in a thick-shell configuration, identifying for the first time in the literature a similarity relation of the theory for the radially normalised scalar field gradient. Our analysis reveals that the chameleon mechanism alters the internal pressure of white dwarfs, leading to a reduction in the stellar radii and masses and shifting the mass-radius curves below those predicted by Newtonian gravity. This lowers also the specific heat of white dwarfs, accelerating their cooling process. Finally, we derive parametric expressions from our results to expedite future analyses of white dwarfs in scalar-tensor theories.