Abstract
Unlike its minimal counterpart, the Next to Minimal supersymmetric Standard Model (NMSSM) allows the possibility that the lightest neutralino could have a mass as small as $\sim 1 {\rm GeV}$ while still providing a significant component of relic dark matter (DM). Such a neutralino can provide an invisible decay mode to the Higgs as well. Further, the observed SM-like Higgs boson ($H_{125}$) could also have an invisible branching fraction as high as $\sim 19\%$. Led by these facts, we first delineate the region of parameter space of the NMSSM with a light neutralino ($M_{{\tilde{\chi}}_{1}^{0}} < 62.5 {\rm GeV}$) that yields a thermal neutralino relic density smaller than the measured relic density of cold dark matter, and is also compatible with constraints from collider searches, searches for dark matter, and from flavor physics. We then examine the prospects for probing the NMSSM with a light neutralino via direct DM detection searches, via invisible Higgs boson width experiments at future $e^+e^-$ colliders, via searches for a light singlet Higgs boson in $2b2\mu$, $2b2\tau$ and $2\mu2\tau$ channels and via pair production of winos or doublet higgsinos at the high luminosity LHC and its proposed energy upgrade. For this last-mentioned electroweakino search, we perform a detailed analysis to map out the projected reach in the $3l+{\rm E{\!\!\!/}_T}$ channel, assuming that chargino decays to $W {\tilde{\chi}}_{1}^{0}$ and the neutralino(s) decay to $Z$ or $H_{125}$ + ${\tilde{\chi}}_{1}^{0}$. We find that the HL-LHC can discover SUSY in just part of the parameter space in each of these channels, which together can probe almost the entire parameter space. The HE-LHC probes essentially the entire region with higgsinos (winos) lighter than 1 TeV (2 TeV) independently of how the neutralinos decay, and leads to significantly larger signal rates.
Highlights
The LHC Run-II has ushered in a new era in terms of energy, luminosity and discovery potential
As in [24] we focus on Mχ01 ≤ 62.5 GeV, that can potentially contribute to invisible decays of the Higgs boson discovered at CERN [27,28,29,30], hereafter referred to as H125
In this article, assuming a standard cosmological scenario, we perform a comprehensive exploration of the light neutralino as a thermal cold dark matter candidate in the next-to-minimal supersymmetric Standard Model (NMSSM) by imposing current low energy, collider and astrophysical constraints
Summary
The LHC Run-II has ushered in a new era in terms of energy, luminosity and discovery potential. Results in [24] indicated that the MSSM parameter space with a light neutralino DM and with a correct or underabundant relic density could be entirely probed via the future dark matter experiments This naturally motivates us to examine the extent to which the considerations of [24] would be altered in the simplest extension of the MSSM, the next-to-minimal supersymmetric Standard Model (NMSSM) [25,26]. In this article, assuming a standard cosmological scenario, we perform a comprehensive exploration of the light neutralino as a thermal cold dark matter candidate in the NMSSM by imposing current low energy, collider and astrophysical constraints. These include flavor physics constraints, LEP bounds, recent results from LHC measurements of the Higgs sector including searches for light.
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