In-medium \Sigma^0-\Lambda Mixing in QCD Sum Rules

The \Sigma^0-\Lambda 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 \theta^S and the vector mixing angle \theta^V. This causes a difference between the particle mixing \theta (= \theta^S + \theta^V) and the anti-particle mixing \bar{\theta} (= \theta^S - \theta^V). From the finite energy sum rules for the \Sigma^0-\Lambda mixing, we find that the in-medium part of the mixing angle has a relation \theta^S_{Med} \simeq - \theta^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 |\bar{\theta} - \theta_0| \simeq 0.39 |(\rho_n - \rho_p)| / \rho_0 with \theta_0, \rho_n, \rho_p and \rho_0 being the vacuum mixing angle, the neutron density, the proton density and the normal nuclear matter density respectively.