Electric dipole moment of the electron and of the neutron

Abstract

It is shown that if Higgs-boson exchange mediates CP violation a significant electric dipole moment for the electron can result. Analogous effects can contribute to the neutron's electric dipole moment at a level competitive with Weinberg's three-gluon operator.PACS numbers: 13.40.Fn, ll.30.Er, 12.15.Cc Ever since the discovery of CP violation' a quarter of a century ago, experimentalists have steadily improved the bounds on the electron dipole moments of the electron 2,3 and of the neutron. 4 In the standard model, these moments are rather small and well below the present experimental bounds. Recently, Weinberg 5 pointed out that in models with CP or T violation carried by Higgs fields, a class of graphs neglected previously by theorists may contribute to the electric dipole moment of the neutron at a level just an order of magnitude below the present bound. Inspired by Weinberg's work, we have found a class of graphs, also neglected previously, which may contribute significantly to the electric dipole moment of the electron. Furthermore, a similar class of graphs competes with and may even dominate Weinberg's effect for the neutron electric dipole moment.In the standard model, the electron electric dipole moment is predicted to be 6 ;SlO~3 8 ecm, which is much smaller than the present bound of 3 ( -1.5 ±5.5 ± 1.5) xlO -26 ecm, as to make experimentalists despair. Indeed, a survey of the literature 7 shows that even in nonstandard models the electron electric dipole moment tends to be very small, typically less than (and usually much less than) 10 ~2 6 cm. To cheer up the experimentalists, one of us has designed a model 8 specifically to produce a large electron dipole moment, perhaps as large as 10~2 5 -10~2 6 ecm. This model requires exotic scalar particles coupling the electron to the r. It is also possible to have a large electron dipole moment in left-rightsymmetric models. 9 In contrast, in this Letter we will stick to the more conservative possibility envisioned by Weinberg 5,10 that there is some CP violation mediated by Higgs-boson exchange. This is possible in the two-Higgs-doublet standard model. l! Encouragingly we find a typical value for d e le which is typically of order 10 ~2 6 cm. Experimentalists are currently working towards limits of a few x 10~2 7 cm, and hope to reach limits near 10~2 8 cm in the future.One of our graphs involves a top quark just as does Weinberg's graph, except that we have pulled the Higgs field "out of the top-quark loop," which reduces what would otherwise have been at least a three-loop effect to a two-loop one. The point is that since a factor of m e is required by chirality in any case, we may as well let an explicit Higgs-boson coupling flip the chirality. We can understand the behavior of this graph by considering the limit m t^> rriH, in which we have in the effective theory (for energies ;Sm/y) the operators v ~l0F llv F^v and v~x()>F^vF^v. By dimension counting, the coefficient of the operator is proportional to the Yukawa coupling of the top quark divided by...

Effects of CP-violating phases on Higgs boson production at hadron colliders in the Minimal Supersymmetric Standard Model

“…We have fixed the former to be 200 GeV, whereas two possible choices of the latter have been adopted, 2.7 and 10 (corresponding to Mq 1,2 = 1000 and 300 GeV, respectively). With regard to this last parameter, tan β, a few considerations have to be made at this point: namely, concerning the so-called 'Barr-Zee type graphs' [34]. Very recently, the corresponding contributions to the electron and neutron EDMs have been calculated at two loops, in Ref.…”

CP-odd correlation in the decay of a neutral Higgs boson intoZZ,W+W−Chang1, Keung2, Phillips3 1993Phys. Rev. D941810View full textAdd to dashboardCite

“…The complex coefficient A is a combination of modeldependent mixing angles. The CP violating effect is proportional [12,13] to Im A 2 = 2Im ARe A. In Higgs boson production at a high energy collider, one expects the CPTeven, CP violating effect to be observable in the angular asymmetry as before.…”

Search for nonstandard modelCPorTviolation at theτ-charm factory

“…These include multi-Higgs doublet model ( including two Higgs doublet model) [3,33], Left-Right symmetric model [34], mirror fermion model [35] and universal soft breaking SUSY model [8] etc. In multi-Higgs doublet model electron [36] and neutron [5] may obtain a large EDM close to current experimental bounds through two loop diagrams, but d τ generated in the model is quite below the TCF observable value. The reason is that d τ is proportional m τ , but not a large fermion mass.…”