Not-so-well-tempered neutralino

Stefano Profumo, Tim Stefaniak, and Laurel Stephenson-Haskins

Phys. Rev. D 96, 055018 – Published 15 September 2017

Abstract

Light electroweakinos, the neutral and charged fermionic supersymmetric partners of the standard model $SU (2) \times U (1)$ gauge bosons and of the two SU(2) Higgs doublets, are an important target for searches for new physics with the Large Hadron Collider (LHC). However, if the lightest neutralino is the dark matter, constraints from direct dark matter detection experiments rule out large swaths of the parameter space accessible to the LHC, including in large part the so-called “well-tempered” neutralinos. We focus on the minimal supersymmetric standard model (MSSM) and explore in detail which regions of parameter space are not excluded by null results from direct dark matter detection, assuming exclusive thermal production of neutralinos in the early universe, and illustrate the complementarity with current and future LHC searches for electroweak gauginos. We consider both bino-Higgsino and bino-wino “not-so-well-tempered” neutralinos, i.e. we include models where the lightest neutralino constitutes only part of the cosmological dark matter, with the consequent suppression of the constraints from direct and indirect dark matter searches.

Received 17 July 2017

DOI:https://doi.org/10.1103/PhysRevD.96.055018

Physics Subject Headings (PhySH)

Particle dark matter Particle decays Particle interactions Supersymmetric models Weakly interacting massive particles

Hypothetical fermions Hypothetical scalars Superpartners

Hadron colliders Lepton colliders

Particles & Fields

Authors & Affiliations

Stefano Profumo^*, Tim Stefaniak^†, and Laurel Stephenson-Haskins^‡

Department of Physics and Santa Cruz Institute for Particle Physics, University of California, Santa Cruz, California 95064, USA

^*profumo@ucsc.edu
^†tistefan@ucsc.edu
^‡lestephe@ucsc.edu

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Issue

Vol. 96, Iss. 5 — 1 September 2017

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Images

Figure 1
Comparison of current and projected constraints in the well-tempered bino-Higgsino neutralino DM scenario in the ( $μ$ , $M_{1}$ ) parameter plane for negative $μ$ (left) and positive $μ$ (right), with $\tan β = 10$ , $M_{2} = 2.5 TeV$ and a pseudoscalar Higgs mass of $M_{A} = 500 GeV$ . The orange regions are excluded by two different LHC searches for $p p \to {\tilde{χ}}_{1}^{\pm} {\tilde{χ}}_{2}^{0} \to W^{\pm} Z {\tilde{χ}}_{1}^{0} {\tilde{χ}}_{1}^{0}$ by the CMS experiment [27, 51] (see text). Projected limits for $100 {fb}^{- 1}$ and $300 {fb}^{- 1}$ of the CMS searches are shown by dashed lines. The exclusion obtained from the LEP chargino mass limit is shown in green. Current and projected (improvement of a factor 2) exclusion limits by the DM direct detection experiment XENON1T [46] are shown as blue shaded areas with varying opacity (see blue text labels). Projected limits from DM indirect detection experiments are indicated by the magenta regions, where the current limit is scaled by factors of 10, 100 and 1000, with high to low opacity. The narrow region that predicts the observed DM relic density is shown in red. An overlaid hatching marks the over-abundant neutralino DM regions, assuming a standard cosmological thermal history. The roughly diagonal and hyperbolic-like gray dotted contours give values for the mass splitting, $Δ m = m_{{\tilde{χ}}_{1}^{\pm}} - m_{{\tilde{χ}}_{1}^{0}}$ , and the DM mass, $m_{{\tilde{χ}}_{1}^{0}}$ , respectively.
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Figure 2
Branching ratios of heavy Higgs boson decays to light electroweakinos (top row) and electroweakino mass spectrum (bottom row) as function of the bino mass parameter $M_{1}$ in the bino-Higgsino neutralino DM scenario, for $μ = - 250 GeV$ (left) and $μ = - 125 GeV$ (right). We again choose $\tan β = 10$ and a pseudoscalar Higgs mass of $M_{A} = 500 GeV$ .
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Figure 3
Branching ratios of heavy Higgs boson decays to light electroweakinos (top row) and electroweakino mass spectrum (bottom row) as function of the Higgsino mass parameter $μ$ in the bino-Higgsino neutralino DM scenario, for $M_{1} = 200 GeV$ . We again choose $\tan β = 10$ and a pseudoscalar Higgs mass of $M_{A} = 500 GeV$ .
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Figure 4
Comparison of current and projected constraints in the well-tempered bino-wino neutralino DM scenario in the ( $M_{2}$ , $M_{2} - M_{1}$ ) parameter plane for $μ = 750 GeV$ (left) and 2.5 TeV (right), with $\tan β = 10$ and a pseudoscalar Higgs mass of $M_{A} = 500 GeV$ . The orange regions are excluded by two different LHC searches for $p p \to {\tilde{χ}}_{1}^{\pm} {\tilde{χ}}_{2}^{0} \to W^{\pm} Z {\tilde{χ}}_{1}^{0} {\tilde{χ}}_{1}^{0}$ by the CMS experiment [27, 51] (see text). Projected limits for $100 {fb}^{- 1}$ and $300 {fb}^{- 1}$ of the CMS searches are shown by dashed lines. The exclusion obtained from the LEP chargino mass limit is shown in green. Current and projected exclusions by the XENON1T DM direct detection experiment are shown as blue shaded areas with varying opacity (see blue text labels). Projected limits from DM indirect detection experiments are indicated by the magenta regions, where the current limit is scaled by factors of 10, 100 and 1000, with high to low opacity. The narrow region that predicts the observed DM relic density (including a $3 σ$ error margin) is shown in red. The roughly horizontal and vertical gray dotted contours give values for the mass splitting, $Δ m = m_{{\tilde{χ}}_{1}^{\pm}} - m_{{\tilde{χ}}_{1}^{0}}$ , and the DM mass, $m_{{\tilde{χ}}_{1}^{0}}$ , respectively.
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Figure 5
Rescaled spin-independent (SI) neutralino-nucleon scattering cross section, $σ_{SI}$ (in pb), in the bino-wino neutralino DM scenario. Left: dependence on $M_{2}$ for fixed $M_{1} = M_{2} - 10 GeV$ , pseudoscalar Higgs mass $M_{A} = 500 GeV$ , $\tan β = 10$ and values of $μ = 750 GeV$ (green), 2.5 TeV (red) and $- 750 GeV$ (magenta). The second $x$ -axis indicates the lightest neutralino mass, $m_{{\tilde{χ}}_{1}^{0}}$ (assuming $μ = 750 GeV$ ). The blue, green and orange filled regions are excluded by LUX, LEP and LHC, respectively, whereas the dashed blue lines show different rescalings of the current limit (see text labels); Right: dependence on $μ$ for lightest neutralino masses of $m_{{\tilde{χ}}_{1}^{0}} = 150 GeV$ (red) and 300 GeV (blue). The parameters are tuned such that the predicted DM relic density, $ρ_{χ}$ , matches its observed value, $ρ_{DM}$ . The second $x$ -axis indicates the Higgsino component of the lightest neutralino, $Z_{13}^{2} + Z_{14}^{2}$ . In the dashed part of the lines $σ_{SI}$ is in conflict with the LUX observations and thus excluded by LUX.
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Figure 6
Illustration of the Higgs funnel mechanism: neutralino DM relic abundance, $Ω h^{2}$ , (left) and rescaled spin-independent neutralino DM-nucleon scattering cross section (right) as a function of $M_{2}$ , for fixed values of $μ = 750 GeV$ , $M_{1} = M_{2} - 10 GeV$ , a pseudoscalar Higgs mass of $M_{A} = 500 GeV$ , and three values of $\tan β = 5$ , 10 and 25. The upper horizontal axis gives the lightest neutralino mass, $m_{{\tilde{χ}}_{1}^{0}}$ , corresponding to the $M_{2}$ values on the lower horizontal axis (assuming $\tan β = 10$ ).
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