Stability of primordial black holes
  Vacuum polarization in a strong field, such as Hawking radiation from black holes, is constrained by the directional metric of strong field vectors. Relative localization of the quanta and the Schwarzschild radius is examined. Concept of thermal equilibrium of excited vacuum is critically analyzed and judged as dis-equilibrium, because virtual modes or particles are mutually independent. The result shows that primordial micro-size black holes (\pmbhs) cannot produce much Hawking radiation via fermions, bosons or thermal photons. Primordial black holes produced in the early epoch of the Big Bang should be very stable over Hubble time and consequently, may constitute a significant part of the cold dark matter in the structural formation of the universe. \pmbhs should be gravitationally highly-condensed as missing mass around galaxies and galaxy clusters, and remain very difficult to observe. 
Yoshiyuki Takahashi