Probing primordial non-Gaussianity with Fast Radio Bursts

TL;DR

Fast radio bursts can be used to probe primordial non-Gaussianity by analyzing their dispersion measure correlations, offering a new way to study early universe physics with large-volume surveys.

Contribution

This paper demonstrates that FRB dispersion measure correlations can constrain primordial non-Gaussianity, providing a novel and competitive method for probing inflationary physics.

Findings

DM correlations are cosmic-variance limited with 10^3-10^4 FRBs

Tomographic analysis can constrain f_NL to around 1

FRBs can probe larger volumes than galaxy surveys

Abstract

Fast radio bursts (FRBs) are astrophysical transients of currently unknown origin, and so far several events have been detected at extragalactic distances. The dispersion measure (DM) of the radio signal is a probe of the integrated electron density along the line of sight and therefore allows to map the electron distribution within the large-scale structure. Since a fraction of electrons gets expelled from galaxies by feedback, they are anticorrelated with halos at large scales and hence the angular DM correlations show a scale-dependent bias caused by primordial non-Gaussianity. Although the signal is weaker than in other probes like galaxy clustering, FRBs can potentially probe considerably larger volumes. We show that while studying the FRB clustering signal requires very large samples, correlations in the DM are cosmic-variance limited on large angular scales with only $\sim 10^{3-4}$ events. A tomographic analysis of the angular DM correlation function can constrain the local primordial bispectrum shape parameter $f_\mathrm{NL}$ to a precision down to ${f_\mathrm{NL}}\sim \mathcal{O}(1)$ depending on assumptions about the FRB redshift distribution and the astrophysical feedback on large scales. This makes FRBs a competitive probe to constrain inflationary physics.