THE SPECTRAL-FUNCTION OF THE RHO-MESON IN NUCLEAR-MATTER

We calculate the modification of a rho meson in nuclear matter through its coupling to resonance-hole states. Starting from a recently propo sed model, we include all four star resonances up to 1.9 GeV. In contr ast to previous works, we include not only resonances that couple to t he rho in a relative p-wave, but also those that couple to an s-wave s tate. In addition, we solve the equation for the rho spectral function self-consistently. We find that s-wave resonances affect the in mediu m spectral function of the rho strongly. Tn the transverse channel the rho meson is, especially at non-zero momentum, completely washed out and can in the presence of nuclear matter no longer be viewed as a res onant excitation of the vacuum. Instead, our model shows a continuum o f possible excitations with the quantum numbers of a transversely pola rized rho. In the longitudinal channel, however, the rho retains its r esonant character in our calculation. As a consequence of the self-con sistent treatment we also find a strong enhancement of the widths of t he included nucleon resonances in medium. (C) 1998 Elsevier Science B. V.