The $q^2$ dependence of the $\rho-\omega$ mixing amplitude is analyzed with the use of the QCD sum rules and the dispersion relation. Going off shell the mixing decreases, changes sign at $q^2 \simeq 0.4 m_{ \rho}^2 > 0$ and is negative in the space like region. Implications of this result to the isospin breaking part of the nuclear force are discussed.
Categories: nucl-th hep-ph