Quantum spinor field in the FRW universe with a constant electromagnetic background

This paper is a natural continuation of our paper Quantum Scalar Field in F RW Universe with Constant Electromagnetic Background, Int. J. Mod. Phys. A1 2, 4837 (1997). We generalize our previous work to the case of a massive sp inor field, which is placed in a FRW universe of a special type with a cons tant electromagnetic field. So as to achieve this, special sets of exact so lutions of the Dirac equation in the background under consideration are con structed and classified. Using these solutions representations for out-in, in-in, and out-out spinor Green functions are explicitly constructed as pro per-time integrals over the corresponding contours in the complex proper-ti me plane. The vacuum-to-vacuum transition amplitude and the number of creat ed particles are found and vacuum instability is discussed. The mean values of the current and of the energy-momentum tensor are evaluated, and differ ent approximations for them are presented. The back reaction related to par ticle creation and to unstable vacuum polarization is estimated in differen t regimes.