Anomalous moments of quarks and leptons from nonstandard WW gamma couplings.

Abstract

Contributions of nonstandard $\mathrm{WW}\ensuremath{\gamma}$ couplings to the four electromagnetic form factors of light quarks and leptons, magnetic and electric dipole moments, anapole moments, and charge radii, have been reevaluated, with a special emphasis on the effects of the locally SU${(2)}_{\mathrm{weak}}$-invariant nonrenormalizable couplings $\ensuremath{\lambda}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\lambda}}$. Previous results for the contribution of the dimension-four anomalous couplings $\ensuremath{\Delta}\ensuremath{\kappa}$ and $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\kappa}}$ are reproduced. The $\ensuremath{\lambda}$ contribution to the charge radius and the anapole moments are found to be logarithmically sensitive to the cutoff scale ($\ensuremath{\Lambda}$), but the contribution of the $\ensuremath{\lambda}$ coupling to the anomalous magnetic moments as well as that of the $\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\lambda}}$ coupling to the electric dipole moments are found to be finite. These finite values are, however, found to be regularization-scheme dependent. The origin of the ambiguities is discussed and we argue that the numerical coefficients depend on the details of the underlying physics that give rise to these nonstandard couplings. Banning an accidental cancellation, we can place an order-of-magnitude upper bound $|\stackrel{\ifmmode \tilde{}\else \~{}\fi{}}{\ensuremath{\lambda}}|\ensuremath{\lesssim}{10}^{\ensuremath{-}4}$ from the experimental limit on the electric dipole moment of the neutron. Some definite predictions for the off-shell form factors are also presented.