Speaker
Description
We examine the region of the parameter space of the Next to Minimal
Supersymmetric Standard Model (NMSSM) with a light neutralino~($M_{\tilde\chi_1^0} \leq~$62.5 GeV) where the SM-like Higgs boson can decay invisibly, the thermal neutralino relic density is smaller than the measured cold dark
matter relic density, and where experimental constraints from LHC searches
and flavor physics are satisfied. We observe allowed regions of parameter space where the lightest neutralino could have a mass as small as $\leq 10~{\rm GeV}$ while still providing a significant component of relic dark matter (DM). 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 that may allow
further exploration of the underlying new physics.