Spinning primordial black holes formed during a matter-dominated era

We study the formation of spinning primordial black holes during an early matter dominated era. Using non-linear 3+1D general relativistic simulations, we compute the efficiency of mass and angular momentum transfer in the process, which we find to be O (10%) and O(5%), respectively. We show that subsequent evolution is important due to the seed PBH accreting non-rotating matter from the background, which decreases the dimensionless spin. Unless the matter era is short, we argue that the final dimensionless spin will be negligible.