Temperature dependence of rho- and a₁-meson masses and mixing of vector and axial-vector correlators

Within a chiral model which provides a good description of the properties of rho and a_1 mesons in vacuum, it is shown that, to order T^2, the rho- and a_1-meson masses remain constant in the chiral limit, even if at tree level they are proportional to the chiral condensate, sigma_0. Numerically, the temperature dependence of the masses turns out to be small also for realistic parameter sets and high temperatures. The weak temperature dependence of the masses is consistent with the Eletsky-Ioffe mixing theorem, and traces of mixing effects can be seen in the spectral function of the vector correlator at finite temperature.