Vacuum expectation values of the energy-momentum tensor of quantized fields in a homogeneous isotropic space-time

Regularization of vacuum expectation values of the stress energy tensor of scalar and spinor fields in homogeneous isotropic space-time is carried out. The cases of flat, spherical and hyperbolical 3-space are considered. Both the contribution of created particles and vacuum polarization by gravitational field are taken into account. The resulting stress energy tensor posesses the nonzero trace for massless fields.