Dark Matter and Enhanced Higgs to Di-photon Rate from Vector-like Leptons

TL;DR

This paper explores an extension of the Standard Model with vector-like leptons, proposing a dark matter candidate and mechanisms to enhance the Higgs to di-photon decay rate, while analyzing experimental constraints and detection prospects.

Contribution

It introduces a model with vector-like leptons that simultaneously addresses dark matter and Higgs decay enhancements, considering experimental and stability constraints.

Findings

Large Higgs di-photon enhancement requires lightest charged lepton near LEP limit.

Relic density favors co-annihilation with small mass difference between leptons.

Constraints from electroweak tests and vacuum stability limit Yukawa couplings.

Abstract

In this paper, we study an extension of the standard model with a vector-like generation of leptons. This model provides a viable dark matter candidate and a possibility to enhance the Higgs decay rate into a pair of photons. We evaluate constraints from electroweak precision tests and from vacuum stability, and find that the latter provide an upper limit on the lepton Yukawa couplings. A large enhancement of the Higgs di-photon rate can therefore only be obtained when the mass of the lightest charged lepton is close to the LEP limit. The relic density constraint suggests a co-annihilation scenario with a small mass difference between the lightest charged and neutral leptons, which also weakens the LEP limit on the lightest charged lepton mass and allows for larger Higgs di-photon decay rates. Cross sections for direct detection of the dark matter candidate are calculated, and prospects for detecting the new particles at the LHC are discussed briefly.