Theta Term in QCD sum rules at Finite Temperature and the Neutron Electric Dipole Moment

Abstract

By using thermal QCD sum rules to investigate the $\bar{\theta}$ induced neutron electric dipole moment $d_n$, we have examined the behaviour of broken CP symmetry at finite temperature. We find that, below the critical temperature, the ratio $\mid {d_n \over \bar{\theta}}\mid$ slightly decreases but survives at temperature effects, implying T nonrestoration of CP-invariance \cite{Chabab}.