Primordial black holes as dark matter

We consider black hole solutions in extended and alternate gravity theories where the geometry of the black hole spacetimes are modified due to extra-dimensional effects. We study the cosmological evolution of primordial black holes in a few such theories. We show that the the phenomenon of accretion of radiation in the radiation dominated em could under certain conditions counterbalance the effect of Hawking evaporation, and this leads to longer lifetime for the black holes in these models. Such black holes could survive till the present era and act as candidates for cold dark matter. We discuss the impact of modified geometry of the black holes on strong gravitational lensing by them, which could be a possible avenue for obtaining observational signatures of extra dimensions.