Bounds on warm dark matter from Schwarzschild primordial black holes

Abstract

We consider light dark matter candidates originated from the evaporation of Schwarzschild primordial black holes, with masses in the range $$10^{-5}$$\n –\n $$10^9$$\n g. These candidates are beyond standard model particles with negligible couplings to the other particles, so that they interact only gravitationally. Belonging to the category of warm dark matter, they nevertheless spoil structure formation, with a softer impact for increasing values of the candidate spin. Requiring such candidates to fully account for the observed dark matter, we find that the scenario of black hole domination is ruled out for all spin values up to 2. For the scenario of radiation domination, we derive upper limits on the parameter $$\\beta $$\n (the primordial black hole energy density at formation over the radiation one), which are less stringent the higher the candidate spin is.