Looking for MACHOs in the Spectra of Fast Radio Bursts

TL;DR

This paper proposes a new method to detect dark matter MACHOs by observing their gravitational lensing effects on fast radio bursts, offering a way to probe distant and compact dark matter objects.

Contribution

It introduces a novel FRB lensing technique to search for MACHOs at cosmological distances, extending beyond traditional microlensing approaches.

Findings

FRB lensing can detect MACHOs in the mass range $10^{-4}$ to 0.1 solar masses.

Interstellar scintillation is a major challenge but can be modeled for realistic scenarios.

Simulations show the method can set competitive limits on dark matter MACHOs.

Abstract

We explore a novel search strategy for dark matter in the form of massive compact halo objects (MACHOs) such as primordial black holes or dense mini-halos in the mass range from $10^{-4}$ to 0.1 solar masses. These objects can gravitationally lens the signal of fast radio bursts (FRBs), producing a characteristic interference pattern in the frequency spectrum, similar to the previously studied femtolensing signal in gamma ray burst spectra. Unlike traditional searches using microlensing, FRB lensing will probe the abundance of MACHOs at cosmological distance scales (~Gpc) rather than just their distribution in the neighborhood of the Milky Way. The method is thus particularly relevant for dark mini-halos, which may be inaccessible to microlensing due to their finite spatial extent or tidal disruption in galaxies. We find that the main complication in FRB lensing will be interstellar scintillation in the FRB's host galaxy and in the Milky Way. Scintillation is difficult to quantify because it heavily depends on turbulence in the interstellar medium, which is poorly understood. We show that, nevertheless, for realistic scintillation parameters, FRB lensing can set competitive limits on compact dark matter object, and we back our findings with explicit simulations.