How light a higgsino or a wino dark matter can become in a compressed scenario of MSSM

Abstract

Higgsinos and Wino have strong motivations for being Dark Matter (DM) candidates in supersymmetry, but their annihilation cross sections are quite large. For thermal generation and a single component DM setup the higgsinos or wino may have masses of around 1 or 2-3 TeV respectively. For such DM candidates, a small amount of slepton coannihilation may decrease the effective DM annihilation cross section. This, in turn reduces the lower limit of the relic density satisfied DM mass by more than 50%. Almost a similar degree of reduction of the same limit is also seen for squark coannihilations. However, on the contrary, for near degeneracy of squarks and higgsino DM, near its generic upper limit, the associated coannihilations may decrease the relic density, thus extending the upper limit towards higher DM masses. We also compute the direct and indirect detection signals. Here, because of the quasi-mass degeneracy of the squarks and the LSP, we come across a situation where squark exchange diagrams may contribute significantly or more strongly than the Higgs exchange contributions in the spin-independent direct detection cross section of DM. For the higgsino-DM scenario, we observe that a DM mass of 600 GeV to be consistent with WMAP/PLANCK and LUX data for sfermion coannihilations. The LUX data itself excludes the region of 450 to 600 GeV, by a half order of magnitude of the cross-section, well below the associated uncertainty. The similar combined lower limit for a wino DM is about 1.1 TeV. There is hardly any collider bound from the LHC for squarks and sleptons in such a compressed scenario where sfermion masses are close to the mass of a higgsino/wino LSP.

Combined collider constraints on neutralinos and charginos

“…The three relevant DM annihilation processes in the early Universe in this context are efficient annihilation of Higgsino DM (potentially also involving coannihilation with similar-mass Higgsino charginos and next-to-lightest neutralinos) or wino DM (potentially involving co-annihilation with similar-mass wino lightest charginos), or resonant annihilation of binos via the SM Higgs or Z boson. Whilst all of these processes have been shown to be effective in the relevant mass range in recent studies [88,157,158], the detailed mixture of the LSP plays a significant role in determining whether the resulting relic density of DM is equal to the full cosmological abundance, or some fraction of it. At a mass of a few tens or hundreds of GeV, pure winos and Higgsinos annihilate too efficiently to produce the full relic density.…”

The past, present and future of the heavier electroweakinos in the light of LHC and other data

“…In ref. [42], authors have shown that this upper limit for higgsino DM mass can be relaxed if a small amount of slepton co-annihilation is present. Note that in our model such a co-annihilation cannot occur as sleptons are much heavier than the LSP.…”

Robustness of dark matter constraints and interplay with collider searches for New Physics

“…One can note that LEP also provides limits for the lightest neutralino, but they can be evaded in specific cases and since our analysis is focussed on dark matter and the lightest neutralino, we prefer not to apply it. The neutralino mass will nevertheless be constrained by the light Higgs signal strength measurements, which can lead to stronger limits than LEP [121][122][123][124][125][126]. Table 4.…”

“…In particular, the diphoton channel favours heavy charginos, stops and charged Higgs bosons [121,122,[206][207][208]. In addition, light Higgs decays into supersymmetric particles are rather limited [121,[123][124][125][126]. These important limits provide strong constraints in the (µ, M 2 ) parameter plane.…”