  This paper shows that accretion of positronium plasma between 0.01 to 14s
after the Big Bang could have created small black holes contributing at least 1
percent of the dark matter present today, with uncertainties ranging from 10
percent or more. General relativistic magnetohydrodynamic (GRMHD) simulations
newly adapted to the early Universe confirm that accretion is due to
magneto-rotational instability (MRI) in a rotating plasma. By contrast with
Bondi accretion producing primordial masses bigger than the Sun, MRI could
produce masses 10^{15-18} g observable by their Hawking radiation contributing
to background gamma rays.
