Electric dipole moment of the neutron from a flavor changing Higgs boson

TL;DR

This paper calculates the neutron electric dipole moment induced by flavor-changing Higgs couplings to quarks, extending previous one-loop analyses to two loops, including QCD corrections, and constrains new physics parameters using experimental bounds.

Contribution

It extends the analysis of neutron EDM contributions from flavor-changing Higgs couplings to two loops and incorporates QCD corrections, providing updated constraints on new physics.

Findings

QCD corrections suppress the neutron EDM estimate by about a factor of ten.

Constraints on the imaginary part of Higgs flavor-changing couplings are of order 10^{-3}.

Neutron EDM bounds imply new physics scale up to 20 TeV if couplings saturate previous bounds.

Abstract

I consider neutron electric dipole moment contributions induced by flavor changing Standard Model Higgs boson couplings to quarks. Such couplings might stem from non-renormalizable $SU(2)_L \times U(1)_Y$ invariant Lagrange terms of dimension six, containing a product of three Higgs doublets. Previously one loop diagrams with such couplings were considered in order to constrain {\it quadratric} expressions of Higgs flavor changing couplings to quarks. In the present paper the analysis is extended to the two loop level, where there are diagrams for electric dipole moments of quarks with a flavor changing Higgs coupling to {\it first order only}. The divergent loops, due to non-renormalisabillity, are parametrized in terms of an ultraviolet cut-off $\Lambda$. I also consider QCD corrections, including the mixing with the color electric dipole moment, while the contribution from the Weinberg operator is found to be negligible. The effect of QCD corrections is to suppress the bare result. Using the current experimental bound on the neutron electric dipole moment, then for cut offs from one to seven TeV, I find a constraint of order $10^{-3}$ for the imaginary part of the {\it product} of the Higgs flavor changing coupling for $(d \rightarrow b)$-transition {\it and} the CKM element $V_{td}$. Assuming that the previous bound of the {\it absolute value} of the Higgs flavor changing coupling for $(d \rightarrow b)$-transition obtained from $B_d - \bar{B_d}$-mixing is saturated, the experimental bound on the neutron electric dipole moment would be reached for the {\it bare} result, {\it if} the cut off were extended up to about ca 20 TeV. However, QCD corrections suppress this result by a factor of order ten, and keep the nEDM below the experimental bound.