In-medium Σ0– Λ mixing in QCD sum rules

Abstract

The Σ 0– Λ mixing angle in isospin-asymmetric nuclear medium is investigated by using QCD sum rules. From the general consideration of the in-medium baryonic correlations, in-medium baryon mixings are shown to have several Lorentz structures such as the scalar mixing angle θ S and the vector mixing angle θ V. This causes a difference between the particle mixing θ (= θ S+ θ V) and the antiparticle mixing θ (= θ S− θ V). From the finite-energy sum rules for the Σ 0– Λ mixing, we find that the in-medium part of the mixing angle has a relation θ S Med∼− θ V Med in the isospin-asymmetric medium. This implies that the medium affects mainly the antiparticle mixing. From the Borel sum rules, we obtain | θ−θ 0|≃0.39|(ρ n −ρ p )|/ρ 0 with θ 0, ρ n, ρ p and ρ 0 being the vacuum mixing angle, the neutron density, the proton density and the normal nuclear matter density, respectively.