Probing Collapsed Dark Matter Halos with Fast Radio Bursts

TL;DR

This paper proposes using gravitational lensing of fast radio bursts to detect dense dark matter substructures caused by self-interacting dark matter, offering a new way to test dark matter models.

Contribution

It introduces a novel method to probe dark matter self-interactions through FRB lensing, focusing on the signatures of core-collapsed halos in upcoming surveys.

Findings

Future FRB surveys can statistically distinguish core-collapsed halos from standard models.

Lensing time delays are sensitive to dark matter self-interaction cross sections.

The method can constrain self-interaction cross sections down to ~18-40 cm^2/g.

Abstract

Observations of ultra-dense substructures in strong lensing systems challenge the standard cosmological model at small scales. Self-interacting dark matter (SIDM), as an alternative to the cold and collisionless dark matter (CDM) of the standard cosmological model, provides a natural mechanism for forming such structures via gravothermal core collapse. We show that strong gravitational lensing of fast radio bursts (FRBs) provides an effective approach to detecting these substructures and probing dark matter self-interactions. Core-collapsed SIDM halos exhibit steeper central density profiles than CDM halos, enhancing the lensing cross section and producing longer time delays between FRB images. We compute lensing properties of core-collapsed subhalos and host halos, including maximal impact parameters and time-delay distributions. We demonstrate that future all-sky monitors, such as BURSTT, SKA2-Low, and SKA2-Mid, which are expected to detect $10^{5}$--$10^{7}$ FRBs over a decade, can measure time-delay distributions with high statistical significance. Modeling collapsed halos with a cored power-law density profile with inner slope $\gamma=3$ and assuming no excess beyond the singular isothermal sphere lens model, we show that our strategy can probe self-interaction cross section strengths of $\sigma_{\text{SI}}/m \gtrsim \min\{18,\, 40\lambda_{\text{sub}}\}\,\text{cm}^2/\text{g}$, where $\lambda_{\text{sub}}$ parameterizes the collapse time of a subhalo relative to that of the isolated case.