p-ω mixing in asymmetric nuclear matter via a QCD sum rule approach

We evaluate the operator product expansion (OPE) for a mixed correlator of the isovector and isoscalar vector currents in the background of the nucleon density with intrinsic isospin asymmetry (i.e., excess of neutrons over protons) and match it with its imaginary part, given by resonances and continuum, via the dispersion relation. The leading density-dependent contribution to p-ω mixing is due to the scattering term, which turns out to be larger than any density dependent piece in the OPE. We estimate that the asymmetric density of n_n-n_p∼2.5×10^-2 fm^-3 induces the amplitude of p-ω mixing, equal in magnitude to the mixing amplitude in vacuum, with the constructive interference for positive and destructive for negative values of n_n-n_p. We revisit sum rules for vector meson masses at finite nucleon density to point out the numerical importance of the screening term in the isoscalar channel, which turns out to be one order of magnitude larger than any density-dependent condensates over the Borel window. This changes the conclusions about the density dependence of m_ω, indicating ∼40 MeV increase at nuclear saturation density.