Neutron electric dipole moment from QCD sum rules

Abstract

The electric dipole moments of nucleons (NEDM, $d\sb{N}$) are calculated using the method of QCD sum rules. Our calculations are based on the parity ($/\!\!\!P$) and time reversal ($/\!\!\!T$) violating parameter $\bar\Theta$ in QCD and establish a functional dependence of the NEDM on $\bar\Theta$, without assuming a perturbative expansion of this symmetry breaking parameter. The results obtained from the QCD sum rules approach are shown to be consistent with the general symmetry constraints on $/\!\!\!P$ and $/\!\!\!T$ in QCD; including the necessity of quark masses, spontaneous chiral symmetry breaking, and the $U\sb{A}$(1) anomaly. Given the current experimental upper bound on the neutron electric dipole moment (nEDM), $d\sb{n}\le 10\sp{-26}e\cdot cm$, we find $\bar\Theta\le 10\sp{-10}$. This is compatible with previous calculations of nEDM using different techniques.