Primordial Black Holes as a Dark Matter Candidate

Abstract

Primordial Black Holes (PBHs) are one of the viable dark matter candidate that comprises some or all of its density in different mass regions. In this context, various constraints suggest that they could entirely comprise dark matter density in the mass window $10^{17}-10^{23}$ g or $10-10^{2} M_{\odot}$ as suggested by observations of black-hole mergers by LIGO/Virgo. PBHs are predicted to have important consequences and can provide unique insights into the physics of early universe. In this thesis, we attempted to constrain PBHs via soft-gamma ray searches by upcoming X and Gamma Imaging Spectrometer (XGIS) telescope array on-board the Transient High-Energy Sky and Early Universe Surveyor (THESEUS) mission. We show that the XGIS-THESEUS mission can potentially provide the strongest bound for $10^{17} \mathrm{~g}<M_{\mathrm{PBH}} \lesssim 3\times 10^{18} \mathrm{~g}$ for non-rotating PBHs. The bounds become more stringent by nearly an order of magnitude for maximally rotating PBHs in the mass range $5\times10^{15}\,{\rm g}\,<\,M_{\rm PBH}\,\lesssim\,10^{19}\,{\rm g}$. We also review the constraints obtained from gravitational lensing signals in the mass region $10^{18}-10^{23}$ g given in the literature.