Modified Higgs branching ratios versus CP and lepton flavor violation

TL;DR

This paper investigates how new physics affecting Higgs decay ratios can induce CP and lepton flavor violations, with electric dipole moments strongly constraining CP-odd effects but less so for lepton flavor violations.

Contribution

It analyzes the constraints from electric dipole moments and lepton flavor violation on new physics models modifying Higgs decay ratios, using effective operators and UV-complete models.

Findings

Electric dipole moments strongly constrain CP-odd contributions to Higgs diphoton decays.

Lepton flavor violating observables impose weaker constraints on Higgs dilepton decay modifications.

Degeneracies in the Higgs sector can enhance CP-violating mixing, affecting constraints.

Abstract

New physics thresholds which can modify the diphoton and dilepton Higgs branching ratios significantly may also provide new sources of CP and lepton flavor violation. We find that limits on electric dipole moments impose strong constraints on any CP-odd contributions to Higgs diphoton decays unless there are degeneracies in the Higgs sector that enhance CP-violating mixing. We exemplify this point in the language of effective operators and in simple UV-complete models with vector-like fermions. In contrast, we find that electric dipole moments and lepton flavor violating observables provide less stringent constraints on new thresholds contributing to Higgs dilepton decays.