Singlet Neighbors of the Higgs Boson

TL;DR

This paper explores how a new scalar singlet near 125 GeV can alter Higgs boson signals, potentially explaining deviations and predicting observable diresonance features at the LHC.

Contribution

It introduces models with a scalar singlet and vector-like matter that modify Higgs decay rates and resonance structures, providing new mechanisms for Higgs property alterations.

Findings

Small Higgs-singlet mixing can enhance diphoton rate.

Higgs decay into a nearby singlet can increase diphoton signals.

Models predict detectable diresonance structures at the LHC.

Abstract

The newly discovered resonance at 125 GeV has properties consistent with the Standard Model (SM) Higgs particle, although some production and/or decay channels currently exhibit O(1) deviations. We consider scenarios with a new scalar singlet field with couplings to electrically charged vector-like matter, focusing particularly on the case when the singlet mass lies within a narrow ~ few GeV window around the Higgs mass. Such a `singlet neighbor' presents novel mechanisms for modifying the observed properties of the Higgs boson. For instance, even a small amount of the Higgs-singlet mixing can lead to a significant enhancement of the apparent diphoton rate. Alternatively, the Higgs may decay into the nearby singlet, along with a very light, very soft mediator particle, in which case there can be O(1) enhancement to the apparent diphoton rate even for ~ TeV-scale charged vector-like matter. We also explore models in which vector-like fermions mix with the SM leptons, causing the simultaneous enhancement of diphoton and suppression of ditau Higgs branching ratios. Our scenario can be tested with the accumulating LHC data by probing for the diresonance structure of the 125 GeV diphoton signal, as well as the relative shift in the resonance location between the diphoton and four-lepton modes.