Spin of primordial black holes

Primordial black holes, formed from rare peaks in the primordial fluctuations zeta, are non-rotating if the RMS (root mean square) fluctuation zeta(rms) is sent to zero. We show that the spin also vanishes at first order in zeta(rms), suggesting the dimensionless spin parameter arms similar to zeta(2)(rms). We identify one quadratic contribution to the spin by calculating (and extrapolating to the formation time) the torque on a black hole due to ambient acoustic waves. For a reasonable density of primordial black holes this implies a percent level spin parameter.