Primordial Black Hole Spin at Formation Under a Shear Bound

Primordial black holes are expected to be born spinning slowly. Unlike stellar collapse, which concentrates the angular momentum of a rotating star, primordial collapse begins from a nearly spherical overdensity in an expanding universe, and acquires rotation only from the tidal torques and anisotropies present at horizon crossing. The headline computed values are: mean a cap = 0.082; high spin frac cap = 0.00e+00; high spin frac nocap = 1.08e-03. This is a simulated and computed study, not a measurement; the code and outputs are deposited alongside the text.