A further study on Palatini f(R)-theories for polytropic stars

TL;DR

This paper investigates polytropic stars within Palatini f(R)-theories, highlighting how singular models extend parameter ranges and proposing the conformal metric as the physical metric, affecting stellar model predictions.

Contribution

It demonstrates how singular models in Palatini f(R)-theories extend parameter ranges and advocates for the conformal metric as the physical metric in stellar models.

Findings

Singular models extend the parameter interval without singularity formation.

The conformal metric can be smoothly matched at stellar surfaces.

Using the conformal metric alters stellar model predictions.

Abstract

After briefly reviewing the results about polytropic stars in Palatini f(R)-theories, we first show how these results rely on the assumption of a regular function f(R). In particular, singular models allow to extend the parameter interval in which no singularity is formed. Furthermore, we present how the conformal metric can be matched smoothly in the cases where the original metric generates a singularity. In fact, the singularity comes from a singular conformal factor which is continuous though not differentiable at the stellar surface. This suggests that the correct metric to be considered as physical is the conformal metric. This is relevant because, even also when matching the original metric is possible, the use of the conformal metric generates different stellar models.