The a1 (1260) as a ρπ Resonance in Nuclear Matter

Abstract

We present a theoretical study of the properties of the a1 (1260) axial-vector resonance in a cold nuclear medium. In the vacuum, the a1 (1260) resonance is generated dynamically from the interactions of a pseudoscalar and vector meson (ρπ and KK̄*) in a coupled channel chiral unitary approach. Medium effects are implemented through the modification of the ρ and π propagators at finite nuclear density from well established microscopic many-body calculations. The in-medium pion spectral function accounts for the coupling to N-hole and Δ-hole excitations including short range correlations, whereas the in-medium ρ incorporates modifications of its virtual pion cloud as well as direct resonance-hole excitations. The resulting in-medium a1 (1260) exhibits significant broadening with increasing density as reflected in the ρπ scattering amplitude. The possible relation of our results with partial restoration of chiral symmetry in nuclear matter is discussed in terms of in-medium Weinberg sum rules.