[Paper Review] Invisible Decays of the Supersymmetric Higgs and Dark Matter

F. Boudjema, G. Bélanger+1 more|ArXiv.org|Jun 28, 2002

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper investigates invisible Higgs decays into neutralinos in supersymmetric models with nonuniversal gaugino masses, showing that such decays can suppress the Higgs boson's diphoton decay rate below 60% of the SM prediction in regions with acceptable dark matter relic density. These scenarios, which could evade detection at the LHC in the γγ channel, correspond to chargino and neutralino masses accessible at the Tevatron, and impose a lower bound on the U(1) gaugino mass parameter M₁ ≥ 20 GeV regardless of other parameters.

ABSTRACT

We discuss effects of the light sparticles on decays of the lightest Higgs in a supersymmetric model with nonuniversal gaugino masses at the high scale, focusing on the `invisible' decays into neutralinos. These can impact significanlty the discovery possibilities of the lightest Higgs at the LHC. We show that due to these decays, there exist regions of the $M_2-μ$ space where the B.R. $(h o γγ)$ becomes dangerously low even after imposing the LEP constraints on the sparticle masses, implying a possible preclusion of its discovery in the $γγ$ channel. We find that there exist regions in the parameter space with acceptable relic density and where the ratio ${B.R. (h o γγ)_{SUSY} \over B.R. (h o γγ)_{SM}}$ falls below 0.6, implying loss of signal in the $γγ$ channel. These regions correspond to $ ilde χ_1^+, ilde χ_2^0$ masses which should be accessible already at the Tevatron. Further we find that considerations of relic density put lower limit on the U(1) gaugino mass parameter $M_1$ independently of $μ, an β$ and $m_0$.

Motivation & Objective

• To analyze the impact of light sparticles on invisible Higgs decays into neutralinos in supersymmetric models with nonuniversal gaugino masses.
• To assess how these invisible decays affect the discovery potential of the lightest Higgs boson at the LHC, particularly in the γγ and bb̄ decay channels.
• To identify regions of parameter space where the Higgs invisible branching ratio is high yet the relic density of neutralinos remains within cosmologically acceptable limits.
• To determine the reach of the Tevatron in probing such parameter regions, especially for chargino and second-lightest neutralino masses.
• To establish a lower bound on the U(1) gaugino mass parameter M₁ that ensures acceptable dark matter relic density independently of μ, tanβ, and m₀.

Proposed method

• The study employs a supersymmetric model with nonuniversal gaugino masses at the high scale, using the MSSM framework with two Higgs doublets.
• It calculates the branching ratio for invisible Higgs decays into neutralino pairs (h → χ̃₁⁰χ̃₁⁰) using one-loop corrections and effective couplings.
• The relic density of neutralino dark matter is computed via thermal freeze-out, including resonant annihilation at the Z and Higgs poles.
• Parameter space scans are performed over M₂, μ, M₁, m₀, and tanβ, with constraints from LEP chargino searches and cosmological observations.
• Branching ratios and relic densities are evaluated using numerical tools, with results visualized in M₂–μ planes for fixed m₀ and tanβ.
• The analysis includes comparisons of the SUSY Higgs diphoton decay rate to the SM prediction, quantifying signal suppression.

Experimental results

Research questions

• RQ1 Can invisible Higgs decays into neutralinos significantly suppress the Higgs diphoton decay rate in supersymmetric models with nonuniversal gaugino masses?
• RQ2 Are there regions in the M₂–μ parameter space where the Higgs invisible decay branching ratio is high enough to jeopardize discovery in the γγ channel, even after applying LEP constraints?
• RQ3 Can such invisible decay scenarios still yield a relic density of neutralinos consistent with cosmological observations (Ωh² ∈ [0.1, 0.3])?
• RQ4 Are the sparticle masses (χ̃₁⁺, χ̃₂⁰) in these regions accessible at the Tevatron Run-II?
• RQ5 What lower bound does the relic density constraint impose on the U(1) gaugino mass parameter M₁, independent of μ, tanβ, and m₀?

Key findings

• In regions of the M₂–μ parameter space with high invisible Higgs branching ratios, the ratio of the Higgs diphoton branching ratio in SUSY to that in the SM falls below 0.6, indicating a significant suppression of the γγ signal.
• These regions with suppressed γγ decay rates correspond to chargino and second-lightest neutralino masses (mχ̃₁⁺ ≈ 250 GeV) that are accessible at the Tevatron Run-II.
• The relic density of neutralino dark matter remains within the cosmologically preferred range (0.1 < Ωh² < 0.3) even for heavier slepton masses, due to efficient annihilation at the Z and Higgs poles.
• A lower bound of M₁ ≥ 20 GeV is required to avoid unacceptably high relic density, independent of μ, tanβ, and m₀, as confirmed by a wide scan over parameter space.
• The invisible decay channel h → χ̃₁⁰χ̃₁⁰ can dominate over the SM decay modes in certain regions, threatening discovery in the γγ and bb̄ channels at the LHC.