# Neutron Stars in Screened Modified Gravity: Chameleon vs Dilaton

## TL;DR

This paper investigates how scalar fields in screened modified gravity models, specifically chameleon and dilaton types, influence neutron star structures and their observable mass-radius relationships.

## Contribution

It provides a numerical analysis of scalar field profiles around neutron stars for chameleon and dilaton models, highlighting degeneracies with the equation of state.

## Key findings

- Chameleon and dilaton behaviors are similar around neutron stars.
- Large degeneracy exists between gravity parameters and the neutron star equation of state.
- Modifications to the mass-radius relationship depend on model parameters.

## Abstract

We consider the scalar field profile around relativistic compact objects such as neutron stars for a range of modified gravity models with screening mechanisms of the chameleon and Damour-Polyakov types. We focus primarily on inverse power law chameleons and the environmentally dependent dilaton as examples of both mechanisms. We discuss the modified Tolman-Oppenheimer-Volkoff equation and then implement a relaxation algorithm to solve for the scalar profiles numerically. We find that chameleons and dilatons behave in a similar manner and that there is a large degeneracy between the modified gravity parameters and the neutron star equation of state. This is exemplified by the modifications to the mass-radius relationship for a variety of model parameters.