Fast radio bursts as a probe of gravity on cosmological scales

TL;DR

This paper investigates how fast radio bursts (FRBs) can improve constraints on Horndeski gravity by analyzing their correlation with cosmic shear, demonstrating potential for enhanced cosmological parameter estimation.

Contribution

It introduces a novel method combining FRB dispersion measures with cosmic shear to constrain modified gravity, specifically Horndeski theories, using advanced modeling and current data.

Findings

FRBs can help disentangle baryonic feedback and neutrino mass effects from gravity parameters.

Including FRBs can improve Horndeski parameter constraints by up to 40%.

Current data provide limited constraints, mainly influenced by priors.

Abstract

We explore the potential for improving constraints on gravity by leveraging correlations in the dispersion measure derived from Fast Radio Bursts (FRBs) in combination with cosmic shear. Specifically, we focus on Horndeski gravity, inferring the kinetic braiding and Planck mass run rate from a stage-4 cosmic shear mock survey alongside a survey comprising $10^4$ FRBs. For the inference pipeline, we utilise the Boltzmann code hi_class to predict the linear matter power spectrum in modified gravity scenarios, while non-linear corrections are obtained from the halo-model employed in HMcode, including feedback mechanisms. Our findings indicate that FRBs can disentangle degeneracies between baryonic feedback and cosmological parameters, as well as the mass of massive neutrinos. Since these parameters are also degenerate with modified gravity parameters, the inclusion of FRBs can enhance constraints on Horndeski parameters by up to $40$ percent, despite being a less significant measurement. Additionally, we apply our model to current FRB data and use the uncertainty in the $\mathrm{DM}-z$ relation to impose limits on gravity. However, due to the limited sample size of current data, constraints are predominantly influenced by theoretical priors. Despite this, our study demonstrates that FRBs will significantly augment the limited set of cosmological probes available, playing a critical role in providing alternative tests of feedback, cosmology, and gravity. All codes used in this work are made publicly available.