Electron-positron plasma in GRBs and in cosmology
  Electron-positron plasma is believed to play imporant role both in the early
Universe and in sources of Gamma-Ray Bursts (GRBs). We focus on analogy and
difference between physical conditions of electron-positron plasma in the early
Universe and in sources of GRBs. We discuss a) dynamical differences, namely
thermal acceleration of the outflow in GRB sources vs cosmological
deceleration; b) nuclear composition differences as synthesis of light elements
in the early Universe and possible destruction of heavy elements in GRB plasma;
c) different physical conditions during last scattering of photons by
electrons. Only during the acceleration phase of the optically thick
electron-positron plasma comoving observer may find it similar to the early
Universe. This similarity breaks down during the coasting phase. Reprocessing
of nuclear abundances may likely take place in GRB sources. Heavy nuclear
elements are then destroyed, resulting mainly in protons with small admixture
of helium. Unlike the primordial plasma which recombines to form neutral
hydrogen, and emits the Cosmic Microwave Background Radiation, GRB plasma does
not cool down enough to recombine.
