Master Thesis Defense by Jo Verwohlt Damm

Supervisor: Radoslav Wojtak & Steen H. Hansen
External supervisor: Steen Hannestad (AU)

Title: Future Cosmological Constraints on Dark Matter with Gravitational Lensing of Fast Radio Bursts

Abstract: The physical nature of dark matter is largely unknown. In the standard cosmological model, a scenario where all dark matter is in the form of cold dark matter (CDM) is generally preferred, however there remains an open window that allows for dark matter in the form of primordial black holes (PBHs) with masses of 20-100M as well as warm dark matter (WDM). Extragalactic transients on millisecond scale - such as Fast Radio Bursts (FRBs), propose the opportunity to study the nature of dark matter when they are gravitationally lensed by PBHs and dark matter halos. In this thesis, we investigate how gravitationally lensed FRBs can be used to constrain dark matter. We find that for an FRB distribution similar to the recently published CHIME/FRB catalogue and for a realistic detection rate of 104 FRBs per year, we can constrain the fraction of dark matter in the form of PBHs to 0.08 % for ML > 20 MSun if less than one out of 10^4 FRBs are lensed. We find that the constraints on dark matter particle mass, as probed by the halo mass function, are much weaker and that it is essentially impractical to distinguish between a CDM and WDM scenario. 104 FRB detections are not sufficient in constraining dark matter particle mass.