Fermionic vacuum densities in higher-dimensional de Sitter spacetime

Fermionic condensate and the vacuum expectation values of the energy m omentum tensor are investigated for twisted and untwisted massive spinor fields in higher dimensional de Sitter spacetime with toroidally compactified spatial dimensions. The expectation values are presented in the form of the sum of corresponding quantities in the uncompactified de Sitter spacetime and the parts induced by non-trivial topology. The latter are finite and renormalizations are needed for the first parts only. Closed formulae are derived for there normalized fermionic vacuum densities in uncompactified odd-dimensional de Sitter spacetimes. It is shown that, unlike to the case of 4-dimensional spacetime, for large values of the mass, these densities are exponentially suppressed. Asymptotic behavior of the topological parts in the expectation values are investigated in the early and late stages of the cosmological expansion. When the comoving lengths of compactified dimensions are much smaller than the de Sitter curvature radius, the leading term in the topological parts coincide with the corresponding quantities for a mass less fermionic field and are conformally related to the corresponding flat spacetime results. In this limit the topological parts dominate the uncompactified de Sitter part and the back-reaction effects should be taken into account. In the opposite limit, for a massive field the asymptotic behavior of the topological parts is damping oscillatory.