Neutrino cooling effect of primordial hot areas in dependence on its
  size
  We consider the temperature dynamics of hypothetical primordial hot areas in
the Universe. Such areas can be produced by the primordial density
inhomogeneities and can survive to the modern era, in particular due to
primordial black hole (PBH) cluster of size $R \gtrsim 1$ pc and more. Here we
concentrate on the neutrino cooling effect which is realized due to reactions
of weak $p\leftrightarrow n$ transitions and $e^{\pm}$ annihilation. The given
neutrino cooling mechanism is found to work in a wide range of parameters. For
those parameters typical for PBH cluster considered, the cooling mechanism is
quite valuable for the temperatures $T \gtrsim 3$ MeV.
