Very Light Charginos and Higgs Decays

TL;DR

This paper investigates how very light charginos in the MSSM can significantly alter Higgs decay rates, especially h→γγ, and proposes search strategies for such scenarios at colliders.

Contribution

It demonstrates that charginos lighter than 100 GeV can cause large deviations in Higgs couplings and decay signals, and presents a hidden light chargino scenario consistent with current constraints.

Findings

Light charginos can enhance the diphoton Higgs decay by up to 70%.

A scenario with a chargino as light as half the Higgs mass is viable and hidden from current searches.

Potential LHC strategies are outlined to detect such light charginos.

Abstract

We explore modifications to the loop-induced Higgs couplings h\gamma\gamma\ and h\gamma Z from light charginos in the Minimal Supersymmetric Standard Model. When the lightest chargino mass is above the naive LEP bound of order 100 GeV the effects are modest, with deviations in the decay branching ratios typically less than 15% from the Standard Model predictions. However, if the charginos are lighter than 100 GeV, more dramatic alterations to these couplings are possible as a consequence of the rise of the one loop form factor. For example, the diphoton signal strength can be enhanced by as much as 70% compared to the Standard Model value. We scrutinize in detail the existing LEP, Tevatron, and LHC searches and present a scenario in which a very light chargino with a mass as light as half the Higgs mass is hidden at LEP and is allowed by all direct collider constraints and electroweak precision tests. The scenario has a sneutrino LSP with a macroscopic decay length of order 10-100 cm. We outline potential search strategies to test this scenario at the LHC.