Testing Einstein's Equivalence Principle with Fast Radio Bursts

TL;DR

This paper demonstrates that fast radio bursts can be used to test Einstein's Equivalence Principle with unprecedented precision, significantly improving previous constraints by analyzing time delays across different frequencies.

Contribution

It introduces a novel method using FRBs to constrain the EEP, achieving the most stringent limits to date on the differential gamma parameter at radio energies.

Findings

Upper limit on gamma differences as low as 4.36×10⁻⁹

Improves previous EEP constraints by 1-2 orders of magnitude

Uses cosmological FRBs to test fundamental physics

Abstract

The accuracy of Einstein's Equivalence Principle (EEP) can be tested with the observed time delays between correlated particles or photons that are emitted from astronomical sources. Assuming as a lower limit that the time delays are caused mainly by the gravitational potential of the Milky Way, we prove that fast radio bursts (FRBs) of cosmological origin can be used to constrain the EEP with high accuracy. Taking FRB 110220 and two possible FRB/gamma-ray burst (GRB) association systems (FRB/GRB 101011A and FRB/GRB 100704A) as examples, we obtain a strict upper limit on the differences of the parametrized post-Newtonian parameter $\gamma$ values as low as $\left[\gamma(1.23\; \rm GHz)-\gamma(1.45\; \rm GHz)\right]<4.36\times10^{-9}$. This provides the most stringent limit up to date on the EEP through the relative differential variations of the $\gamma$ parameter at radio energies, improving by 1 to 2 orders of magnitude the previous results at other energies based on supernova 1987A and GRBs.