Electric dipole and magnetic quadrupole moments of the W boson via a CP-violating HWW vertex in effective Lagrangians

The possibility of nonnegligible W electric dipole (μ˜_W) and magnetic quadrupole (Q˜_W) moments induced by the most general HWW vertex is examined via the effective Lagrangian technique. It is assumed that new heavy fermions induce an anomalous CP-odd component of the HWW vertex, which can be parametrized by an SU_L(2)×U_Y(1)-invariant dimension-six operator. This anomalous contribution, when combined with the standard model CP-even contribution, leads to CP-odd electromagnetic properties of the W boson, which are characterized by the form factors Δκ˜ and ΔQ˜. It is found that Δκ˜ is divergent, whereas ΔQ˜ is finite, which reflects the fact that the latter cannot be generated at the one-loop level in any renormalizable theory. Assuming reasonable values for the unknown parameters, we found that μ˜_W∼3-6×10^-21   e·cm, which is 8 orders of magnitude larger than the SM prediction and close to the upper bound derived from the neutron electric dipole moment. The estimated size of the somewhat less-studied Q˜_W moment is of the order of -10^-36   e·cm², which is 15 orders of magnitude above the SM contribution.