In-medium Σ^0-ΛMixing in QCD Sum Rules

Abstract

The Σ^0-Λmixing 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 anti-particle mixing \barθ (= θ^S - θ^V). From the finite energy sum rules for the Σ^0-Λmixing, we find that the in-medium part of the mixing angle has a relation θ^S_{Med} \simeq - θ^V_{Med} in the isospin-asymmetric medium. This implies that the medium affects mainly the anti-particle mixing. From the Borel sum rules, we obtain |\barθ - θ_0| \simeq 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.