Speaker
Description
The observations of ultra-dense substructures in strong lensing systems challenge the standard
cosmology model at small scales. Self-interacting dark matter (SIDM), as one of the alternatives
to the cold collisionless dark matter (CDM) of the standard cosmology model, provides a natural
mechanism for forming such structures via gravothermal core-collapsing. We show that strong grav-
itational lensing of fast radio bursts (FRBs) provides a new way to effectively probe these structures
and to understand 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 model the SIDM core-collapsed halo with a power-law profile
whose center is cored, and compute lensing properties for subhalo and host halo lensing, including
maximal impact parameters and time-delay distributions. Future observatories, such as BURSTT,
SKA2-Low, and SKA2-Mid, could detect 105–106 FRBs over a decade, yielding statistically sig-
nificant time-delay distributions that can probe core-collapse parameters of SIDM halos including
self-interaction cross section strengths to σ/m ≲ min{18 cm2/g, 40λsub cm2/g}.
