29 v 1 1 6 Ju n 20 00 The ρ Meson in a Nuclear Medium

In this work, propagation properties of the ρ meson in symmetric nuclear matter are studied. We make use of a coupled channel unitary approach to meson-meson scattering, calculated from the lowest order Chiral Perturbation Theory (χP T) lagrangian including explicit resonance fields. Low energy chiral constraints are considered by matching our expressions to those of one loop χP T. To account for the medium corrections, the ρ couples to ππ and K ¯ K pairs which are properly renormalized in the nuclear medium. 1 Description of the model We study the ρ propagation properties by obtaining the ππ and K ¯ K scattering amplitudes in the I = 1 channel. Our states in the isospin basis are |ππ > = 1 2 |π + π − − π − π + > |KK > = 1 √ 2 |K + K − − K 0 K 0 >. (1) Tree level amplitudes are obtained from the lowest order χP T and explicit resonance field lagrangians of refs. [1], [2]. We collect this amplitudes in a 2 × 2 K matrix whose elements are K 11 (s) = 1 3 p 2 1 f 2