Gravitational Lensing in Modified Gravity: A case study for Fast Radio Bursts

TL;DR

This paper investigates how modified gravity theories affect gravitational lensing of Fast Radio Bursts and uses observations to constrain dark matter composed of primordial black holes, revealing a screening effect similar to plasma scattering.

Contribution

It introduces a generic modified gravity framework to analyze lensing effects on Fast Radio Bursts and constrains primordial black hole dark matter fraction within this context.

Findings

Modified gravity induces a screening effect on gravitational lensing.

Fast Radio Burst observations constrain primordial black hole dark matter.

The screening effect mimics plasma scattering in lensing phenomena.

Abstract

Over the last few decades, a plethora of modifications to general relativity have been proposed to solve a host of cosmological and astrophysical problems. Many modified gravity models are now ruled out with further astrophysical observations; some theories are still viable, with, at best, bounds on their parameters set by observations to date. More recently, observations of Fast Radio Bursts have proven to be remarkably powerful tools to constrain cosmology and fundamental physics. In this work, we consider a generic modified gravity theory and consider the implications for gravitational lensing with Fast Radio Bursts. We use a set of Fast Radio Burst observations to constrain the fraction of dark matter made up of primordial black holes in such a theory. We further show that modified gravity adds a screening effect on gravitational lensing similar to the case when there is plasma in the path of the light ray acting as a scattering screen.