Early evolution of fully convective stars in scalar-tensor gravity

TL;DR

This paper investigates how scalar-tensor gravity theories, specifically DHOST models, alter the early evolutionary phases of fully convective low-mass stars, including contraction, lithium burning, and main sequence entry.

Contribution

It introduces the first detailed analysis of early stellar evolution under DHOST scalar-tensor gravity, highlighting modifications to Hayashi tracks and stellar age estimates.

Findings

Hayashi tracks are shifted in scalar-tensor gravity.

Star ages are significantly affected by the modified gravity parameters.

Early evolutionary phases show observable differences from standard models.

Abstract

In this work, the early evolution of low-mass fully convective stars is studied in the context of DHOST (degenerate higher order scalar-tensor) theories of gravity. Although it is known that the hydrostatic equilibrium equation is modified for scalar-tensor gravity, the consequent modifications to the early evolution phases of a star were not explored in this framework. With this in mind, we consider three evolutionary phases - contraction to the main sequence, lithium burning and entrance to the main sequence - and investigate how each of these phases is affected by the theory's parameter. Taking these effects into account, we are able to show, among other things, that the Hayashi tracks are shifted and the star's age is considerably modified.