Interpretation of the neutron electric dipole moment: Possible relationship to ‖ε’‖

Abstract

Recent measurements of D, indicate that it may be of order GF (milliweak), which is much larger than predicted by the Kobayashi-Maskawa (KM) model. The predicted KM moment is shown to be small because it is of second order in GF (superweak) and suppressed by the Glashow-Iliopoulos-Maiani (GIM) mechanism. GIM cancellations have their largest effect on the calculation of the moment of a single quark so that W-exchange contributions between pairs of quarks dominate D,, in the KM model. Experimental confirmation that D, is of order GF (in the range 1 0 -~' -1 0 -~~ e cm) would require a T-violating phase between the P-conserving and P-violating first-order weak interactions, as occurs in the Weinberg model. Any such T violation would lead to a relationship between E' and D, of the form 1 D, 1 -IE'~. We estimate the ratio ID, / €' I for the Weinberg model, andshow that it is consistent with current data on D,, / E ' / E~, and It-1. However, the current data are also consistent with D, =E'=O, SO that a firm conclusion cannot be drawn now.