Subtracted dispersion relations for in-medium meson correlators in QCD sumrules

We analyze subtracted dispersion relations for meson correlators at finite baryon density and temperature. Such relations are needed for QCD sum rules . We point out the importance of scattering terms, as well as finite, well- defined subtraction constants. Both are necessary for consistency, in parti cular for the equality of the longitudinal and transverse correlators in th e limit of vanishing three-momentum of mesons relative to the medium. We pr esent detailed calculations in various mesonic channels for the case of the Fermi gas of nucleons. (C) 1999 Elsevier Science B.V. All rights reserved.