Strong CP problem, Neutron EDM and Thermal QCD sum rules

The behaviour of the broken CP symmetry at finite temperature is examined. This is achieved through the investigation of the neutron electric dipole moment $d_n$ induced by $\theta$-term. By using thermal QCD sum rules, we find that below the critical temperature, the ratio $\mid {d_n \over \bar{\theta}}\mid$ slightly decreases but survives at temperature effects. This evolution implies that CP remains broken at finite temperature as required by Baryogenesis \cite{Chabab}.