Analytical properties of mean two-particle density matrix

The analytical properties of the mean two-particle density matrixZ(t)=dR₁ dR₂ <_c(R₁:R₂;t)(R₁,R₂;t)> in the right-hand halfplane of the complex variable t is considered; herec,v(R₁,R₂; t) are single-particle density matrices. It is proven that, in the case of a Gaussian field, the function Z(t) is analytical in the region Ret > 0. It is shown that the frequency dependence of the light-absorption coefficient in disordered semiconductors is determined by the asymptote of the function Z(t) as t.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 46–50, June, 1987.