Scalar susceptibilities and electromagnetic thermal mass differences in chiral perturbation theory

We make a thermal analysis of the light scalar susceptibilities using SU(3)-chiral perturbation theory to one-loop order, taking into account the QCD source of isospin breaking (IB), i.e. corrections coming from m u ≠ m d . The value of the connected scalar susceptibility in the infrared regime, the one relevant when approaching chiral symmetry restoration, and below the critical temperature is found to be entirely dominated by the π 0 – η mixing, which leads to model-independent O ( ϵ 0 ) corrections, where ϵ ∼ m d − m u , in the combination χ u u − χ u d of flavour breaking susceptibilities. We also present preliminary results for the corrections to the real part of the pion self-energy at next-to-leading order in SU(2)-chiral perturbation theory, taking into account electromagnetic interaction. The results for zero and finite temperature for the charged and neutral pions are given in terms of the 3-momentum of the external pion, and their difference is calculated to this order, stressing the fact that, at low and moderate temperature, the mass splitting M π ± − M π 0 grows with temperature for, at least, non-zero charged pion mass running inside the loops.