Exotic Decays of the 125 GeV Higgs Boson

TL;DR

The paper presents a comprehensive framework for exotic decays of the 125 GeV Higgs boson, outlining how the Higgs can act as a portal to hidden sectors and weakly coupled new states. It systematically catalogs decay topologies (involving scalars, fermions, vectors) and surveys a broad spectrum of models (SM+S, 2HDM+S, MSSM/NMSSM, Little Higgs, Hidden Valleys) that yield h→4-body, semi-invisible, and fully invisible final states. For each scenario, the authors summarize theoretical motivation, existing collider studies, and practical search strategies, including reinterpretations of Run 1 data and proposals for Run 2. They emphasize the discovery potential of dedicated exotic-Higgs analyses, discuss trigger/practical considerations, and provide benchmark points to guide future experimental efforts. The work culminates in detailed recommendations and a prioritization of searches across multiple final states, highlighting the Higgs boson’s unique sensitivity to new weakly coupled sectors and its role as a gateway to BSM physics.

Abstract

We perform an extensive survey of non-standard Higgs decays that are consistent with the 125 GeV Higgs-like resonance. Our aim is to motivate a large set of new experimental analyses on the existing and forthcoming data from the Large Hadron Collider (LHC). The explicit search for exotic Higgs decays presents a largely untapped discovery opportunity for the LHC collaborations, as such decays may be easily missed by other searches. We emphasize that the Higgs is uniquely sensitive to the potential existence of new weakly coupled particles and provide a unified discussion of a large class of both simplified and complete models that give rise to characteristic patterns of exotic Higgs decays. We assess the status of exotic Higgs decays after LHC Run 1. In many cases we are able to set new nontrivial constraints by reinterpreting existing experimental analyses. We point out that improvements are possible with dedicated analyses and perform some preliminary collider studies. We prioritize the analyses according to their theoretical motivation and their experimental feasibility. This document is accompanied by a website that will be continuously updated with further information: http://exotichiggs.physics.sunysb.edu.

Figures (36)

• Figure 1: Sensitivity of a 125 GeV Higgs to light weakly coupled particles. Left: Exotic Higgs branching fraction to a singlet scalar $s$ versus the singlet's mass $m_s$, assuming the interaction Eq. (\ref{['eq:HtoS']}) is solely responsible for the $h\rightarrow ss$ decay. If the interaction in Eq. (\ref{['eq:HtoS']}) generates the $s$ mass, the result is the orange curve; the other curves are for fixed and independent values of $\zeta$ and $m_s$. Right: Exotic Higgs branching fraction to a new fermion $\psi$ interacting with the Higgs as in Eq. (\ref{['eq:HtoPsis']}) to illustrate the sensitivity of exotic Higgs decay searches to high scales, here $\Lambda$. We take here $\mu = m_\psi$.
• Figure 2: The exotic Higgs decay topologies we consider in this document, along with the labels we use to refer to them. Every intermediate line in these diagrams represents an on-shell, neutral particle, which is either a $Z$-boson or a BSM particle.
• Figure 3: Size of the cubic coupling $\mu_v$ in units of Higgs expectation value $v$ to yield the indicated $h \rightarrow s s$ branching fraction as a function of singlet mass, as given by Eq. (\ref{['eq:GammahssSMS']}).
• Figure 4: Left: Branching ratios of a CP-even scalar singlet to SM particles, as function of $m_{s}$. Right: Branching ratios of exotic decays of the 125 GeV Higgs boson as function of $m_s$, in the SM + Scalar model described in the text, scaled to ${\mathrm{Br}}(h\rightarrow ss) = 1$. Hadronization effects likely invalidate our simple calculation in the shaded regions.
• Figure 5: Required mixing angle between the doublet and singlet-sector pseudoscalar for $\mathrm{Br}(h \rightarrow a Z) = 10\%$, assuming no other exotic Higgs decays and $\alpha = \pi/2 - \beta$ (decoupling limit).