Response function including collisions for an interacting fermion gas

The response function of an interacting fermion gas is considered in the en tire ((k) over right arrow,omega) space. Applying a generalized linear resp onse theory, it is expressed in terms of determinants of equilibrium correl ation functions, which allow for a systematic perturbative treatment. The r elation to dynamical local-field factors is given. As a special case, the d ielectric function is evaluated for two-component (hydrogen) plasmas at arb itrary degeneracies. Collisions are treated in Born approximation leading t o a ((k) over right arrow,omega)-dependent collision integral. The link to the dynamical conductivity is given in the long-wavelength limit. Sum rules are discussed. [S1063-651X(99)50309-7].