Speaker
Description
Unveiling the true nature of Dark Matter (DM), which manifests itself only through gravity, is one of the principal quests in physics. Leading candidates for DM are weakly interacting massive particles (WIMPs) or ultralight bosons (axions), at opposite extremes in mass scales,that have been postulated by competing theories to solve deficiencies in the Standard Model of particle physics. Whereas DM WIMPs behave like discrete particles (ρDM), quantum interference between DM axions is manifested as waves (ψDM). In my talk, I present our research (Amruth et al. Nature Astronomy (2023)) which shows that gravitational lensing leaves signatures in multiply-lensed images of background galaxies that reveal whether the foreground lensing galaxy inhabits a ρDM or ψDM halo. Whereas ρDM lens models leave well documented anomalies between the predicted and observed brightnesses and positions of multiply-lensed images, ψDM lens models correctly predict the level of anomalies left over by ρDM lens models. More challengingly, when subjected to a battery of tests for reproducing the quadruply-lensed triplet images in the system HS 0810+2554, ψDM is able to reproduce all aspects of this system whereas ρDM often fails. The ability of ψDM to resolve lensing anomalies even in demanding cases like HS 0810+2554, together with its success in reproducing other astrophysical observations, tilt the balance toward new physics invoking axions. The ongoing JWST mission, and upcoming telescopes such as Euclid and the Square Kilometer Array will provide an abundance of lensing observations that will light the way to understanding the mystery of dark matter.
