A Fresh Look into the Neutron EDM and Magnetic Susceptibility
Résumé
We reexamine the estimate of the neutron Electric Dipole Moment (NEDM) fromchiral and QCD spectral sum rules (QSSR) approaches. In the former, we evaluatethe pion mass corrections which are about 5% of the leading Log. results.However, the chiral estimate can be affected by the unknown value of therenormalizaton scale nu. For QSSR, we analyze the effect of the nucleoninterpolating currents on the existing predictions. We conclude that previousQSSR results are not obtained within the optimal choice of these operators,which lead to an overestimate of these results by about a factor 4. The weakestupper bound |theta|< 2 10^-9 for the strong CP-violating angle is obtained fromQSSR, while the strongest upper bound |theta|< 1.3 10^-10 comes from the chiralapproach evaluated at the scale \nu=M_N. We also re-estimate the protonmagnetic susceptibility, which is an important input in the QSSR estimate ofthe NEDM.