Effective Lagrangian approach to fermion electric dipole moments induced by aCP-violatingWWγvertex

Abstract

The one-loop contribution of the two CP-violating components of the W W γ vertex, κγ W ρµ , on the electric dipole moment (EDM) of fermions is calculated using dimensional regularization and its impact at low energies reexamined in the light of the decoupling theorem. The Ward identities satisfied by these couplings are derived by adopting a SUL(2) × UY (1)-invariant approach and their implications in radiative corrections discussed. Previous results onκγ , whose bound is updated to |κγ | < 5.2 × 10 −5 , are reproduced, but disagreement with those existing forλγ is found. In particular, the upper bound |λγ | < 1.9 × 10 −2 is found from the limit on the neutron EDM, which is more than 2 orders of magnitude less stringent than that of previous results. It is argued that this difference between theκγ andλγ bounds is the one that might be expected in accordance with the decoupling theorem. This argument is reinforced by analyzing careful the low-energy behavior of the loop functions. The upper bounds on the W EDM, |dW | < 6.2 × 10 −21 e · cm, and the magnetic quadrupole moment, |QW | < 3 × 10 −36 e · cm 2 , are derived. The EDM of the second and third families of quarks and charged leptons are estimated. In particular, EDM as large as 10−20 e · cm and 10 −21 e · cm are found for the t and b quarks, respectively.

Searches forCP-violating dimension-6 electroweak gauge boson operators

“…But as we shall see below, any result obtained with a momentum cut-off is unreliable. The next smallest is the result of Novales-Sánchez & Toscano [3], obtained using M S, which is suppressed by a factor m 2 f /m 2 W , where m f is a light quark mass, relative to other results. In [3], two purported explanations are given for the suppression.…”

“…In answer to the first question, we have found five independent computations in the literature (see Table 1) of the diagrams of Fig. 1; no two sets of authors agree on the result, with one set [3] suggesting a suppression by a factor ∼ 10 −10 , compared to a naïve estimate. Another group of authors [4] could even be said to not agree with themselves, in that their result depends on how the regularization is performed, and in fact can take any value.…”

“…1. If custodial symmetry suppresses the EDM, then the result quoted in [3] should vanish in this same limit, but it does not. In fact, custodial symmetry does not imply a constraint on either diagram; rather it relates the two diagrams, which sum to zero in the limit m u = m d .…”

“…µ and the coefficients are related by c W α γ = s W α Z . 4 The strong constraint from the neutron EDM 3 The operator OZ also contributes directly to the EDM via 2-loop diagrams, but we do not consider them here. 4 To make the gauge invariance more manifest, write the operator as OW = W + µ ν W − ν λW 3λ µ = then implies that there is no sensitivity to α Z at the LHC.…”

Electric dipole moments of charged leptons at one loop in the presence of massive neutrinos

“…In particular, diverse investigations as, for instance, those performed in Refs. [27][28][29][30][31][32][33][34][35][36][37][38][39], have explored the generation of electric dipole moments of elementary particles through CP violation characterizing new-physics formulations. Among all the electric dipole moments of elementary particles, that of the electron is, doubtless, the one which has been most stringently bounded [40,41].…”