Exotic Leptons: Higgs, Flavor and Collider Phenomenology

TL;DR

This paper explores how adding vector-like leptons with non-standard hypercharges to the standard model can significantly affect Higgs decay rates, electric dipole moments, and collider signatures, with implications for current experimental constraints.

Contribution

It introduces new hypercharge assignments for vector-like leptons, analyzing their impact on Higgs decays, vacuum stability, and collider phenomenology, which were not previously studied.

Findings

Modified Higgs to gamma gamma decay rates in the 300 GeV - 1 TeV mass range.

Constraints from electric dipole moments and precision observables.

LHC signatures with multiple light leptons or taus probe parameter space.

Abstract

We study extensions of the standard model by one generation of vector-like leptons with non-standard hypercharges, which allow for a sizable modification of the h -> gamma gamma decay rate for new lepton masses in the 300 GeV - 1 TeV range. We analyze vaccum stability implications for different hypercharges. Effects in h -> Z gamma are typically much smaller than in h -> gamma gamma, but distinct among the considered hypercharge assignments. Non-standard hypercharges constrain or entirely forbid possible mixing operators with standard model leptons. As a consequence, the leading contributions to the experimentally strongly constrained electric dipole moments of standard model fermions are only generated at the two loop level by the new CP violating sources of the considered setups. We derive the bounds from dipole moments, electro-weak precision observables and lepton flavor violating processes, and discuss their implications. Finally, we examine the production and decay channels of the vector-like leptons at the LHC, and find that signatures with multiple light leptons or taus are already probing interesting regions of parameter space.