Effect of vector--axial-vector mixing to dilepton spectrum

In this write-up we summarize main results of our recent analyses on the mixing between transverse rho and a1 mesons in hot and/or dense matter. We show that the axial-vector meson contributes significantly to the vector spectral function in hot matter through the mixing. In dense baryonic matter, we include a mixing through a set of omega rho a1 -type interactions. We show that a clear enhancement of the vector spectral function appears below \sqrt{s}=m_\rho for small three-momenta of the rho meson, and thus the vector spectrum exhibits broadening.