π+-π0 mass difference at finite temperature

The electromagnetic mass difference of pions at finite temperature is computed. The finite temperature contribution to the quadratic mass difference of charged and neutral pions is obtained to be παT2, neglecting the corrections due to the rho and A1 mesons. It has the same sign as the zero temperature value and is comparable to it in magnitude around T = 200 MeV. The calculation is also done in case of supersymmetric QCD where it is known that the mass difference is zero at T = 0. The results may have implications for cosmology and for relativistic heavy ion collisions. (orig.)