Light scalar susceptibilities and the $\pi^0-\eta$ mixing

Abstract

We have performed a thermal analysis of the light scalar susceptibilities in the context of SU(3)-Chiral Perturbation Theory to one loop taking into account the QCD source of isospin breaking (IB), i.e corrections coming from $m_u\neq m_d$. We find that the value of the connected scalar susceptibility in the infrared regime and below the critical temperature is entirely dominated by the $\pi^0-\eta$ mixing, which leads to model-independent $\mathcal{O}(\epsilon^0)$ corrections, where $\epsilon\sim m_d-m_u$, in the combination $\chi_{uu}-\chi_{ud}$ of flavour breaking susceptibilities.