Abstract
In the standard model (SM), the coupling of the Higgs boson to electrons is real and very small, proportional to the electron mass. New physics could significantly modify both real and imaginary parts of this coupling. We discuss experiments which are sensitive to the Higgs-electron coupling and derive the current bounds on new physics contributing to this coupling. The strongest constraint follows from the ACME bound on the electron electric dipole moment (EDM). We calculate the full analytic two-loop result for the electron EDM and show that it bounds the imaginary part of the Higgs-electron coupling to be less than 1.7 x 10^-2 times the SM electron Yukawa coupling. Deviations of the real part are much less constrained. We discuss bounds from Higgs decays, resonant Higgs production at electron colliders, Higgs mediated B -> e^+ e^- decays, and the anomalous magnetic moment of the electron. Currently, the strongest constraint comes from h -> e^+ e^- at the LHC, bounding the coupling to be less than ~600 times the SM Yukawa coupling. Important improvements can be expected from future EDM measurements as well as from resonant Higgs production at a next-generation high-luminosity e^+ e^- collider.
Highlights
We briefly discuss how higher-dimensional operators can modify the coupling of the Higgs to electrons
We calculate the full analytic two-loop result for the electron electric dipole moment (EDM) and show that it bounds the imaginary part of the Higgs-electron coupling to be less than 1.7×10−2 times the standard model (SM) electron Yukawa coupling
In appendix B we show that in the Standard Model the Higgs electron coupling is necessarily suppressed by the electron mass to all loop orders
Summary
Within the SM, both the electron mass me and the Higgs-electron coupling geeh are completely determined by the Yukawa coupling ye of the first generation leptons to the Higgs doublet φ, LSM ⊃ yeSMLφeR + h.c. Where M is a new-physics scale, c0 and c2 are complex couplings, and the c1 couplings are real Such operators could arise from mixing of the leptons with heavy vector-like fermions, from mixing of the Higgs with a heavy scalar doublet, or from the exchange of new vector bosons (see figure 1). The operators proportional to c1L and c1R do modify the real part of the Higgs-electron coupling; after integrating by part and applying the equations of motion one sees that these contributions are suppressed by a factor me/M in addition to v/M and are too small to be interesting. One should keep in mind that geeh geSeMh is only possible if there is a significant cancellation between the contributions to the electron mass coming from the Yukawa coupling and the higher-dimensional operator, cf eq (2.5). Throughout this article we set all couplings of the Higgs boson to particles other than the electron to their SM values
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