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Authors
L. Bergstrom
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We investigate the possibility to detect neutralino dark matter in a scenario in which the galactic dark halo is clumpy. We find that under customary assumptions on various astrophysical parameters, the antiproton and continuum gamma-ray signals from neutralino annihilation in the halo put the strongest limits on the clumpiness of a neutralino halo. We argue that indirect detection through neutrinos from the Earth and the Sun should not be much affected by clumpiness. We identify situations in parameter space where the gamma-ray line, positron and diffuse neutrino signals from annihilations in the halo may provide interesting signals in upcoming detectors.
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We investigate if the gamma ray halo, for which recent evidence has been found in EGRET data, can be explained by neutralino annihilations in a clumpy halo. We find that the measured excess gamma ray flux can be explained through a moderate amount of clumping in the halo. Moreover, the required amount of clumping implies also a measureable excess of antiprotons at low energies, for which there is support from recent measurements by the BESS collaboration. The predicted antiproton fluxes resulting from neutralino annihilations in a clumpy halo are high enough to give an excess over cosmic-ray produced antiprotons also at moderately high energies (above a few GeV). This prediction, as well as that of one or two sharp gamma lines coming from annihilations into 2 gammas or Z gamma can be tested in upcoming space-borne experiments like AMS and GLAST.
In the supersymmetric (SUSY) standard model, the lightest neutralino may be the lightest SUSY particle (LSP), and it is is a candidate of the dark matter in the universe. The LSP dark matter might be produced by the non-thermal process such as heavy particle decay after decoupling of the thermal relic LSP. If the produced LSP is relativistic, and does not scatter enough in the thermal bath, the neutralino LSP may contribute as the warm dark matter (WDM) to wash out the small scale structure of O(0.1) Mpc. In this letter we calculate the energy reduction of the neutralino LSP in the thermal bath and study whether the LSP can be the WDM. If temperature of the production time T_I is smaller than 5MeV, the bino-like LSP can be the WDM and may contribute to the small-scale structure of O(0.1) Mpc. The Higgsino-like LSP might also work as the WDM if T_I< 2MeV. The wino-like LSP cannot be the WDM in the favoured parameter region.
We investigate the current status of the light neutralino dark matter scenario within the minimal supersymmetric standard model (MSSM) taking into account latest results from the LHC. A discussion of the relevant constraints, in particular from the dark matter relic abundance, leads us to a manageable simplified model defined by a subset of MSSM parameters. Within this simplified model we reinterpret a recent search for electroweak supersymmetric particle production based on a signature including multi-taus plus missing transverse momentum performed by the ATLAS collaboration. In this way we derive stringent constraints on the light neutralino parameter space. In combination with further experimental information from the LHC, such as dark matter searches in the monojet channel and constraints on invisible Higgs decays, we obtain a lower bound on the lightest neutralino mass of about 24 GeV. This limit is stronger than any current limit set by underground direct dark matter searches or indirect detection experiments. With a mild improvement of the sensitivity of the multi-tau search, light neutralino dark matter can be fully tested up to about 30 GeV.
In spite of rapid experimental progress, windows for light superparticles remain. One possibility is a ~100 GeV tau slepton whose t-channel exchange can give the correct thermal relic abundance for a relatively light neutralino. We pedagogically review how this region arises and identify two distinct scenarios that will be tested soon on multiple fronts. In the first, the neutralino has a significant down-type higgsino fraction and relatively large rates at direct detection experiments are expected. In the second, there is large mixing between two relatively light staus, which could lead to a significant excess in the Higgs boson branching ratio to photons. In addition, electroweak superpartners are sufficiently light that direct searches should be effective.
It is widely believed that dark matter exists within galaxies and clusters of galaxies. Under the assumption that this dark matter is composed of the lightest, stable supersymmetric particle, assumed to be the neutralino, the feasibility of its indirect detection via observations of a diffuse gamma-ray signal due to neutralino annihilations within M31 is examined. To this end, first the dark matter halo of the close spiral galaxy M31 is modeled from observations, then the resultant gamma-ray flux is estimated within supersymmetric model configurations. We conclude that under favorable conditions such as the rapid accretion of neutralinos on the central black hole in M31 and/or the presence of many clumps inside its halo with $r^{-3/2}$ inner profiles, a neutralino annihilation gamma-ray signal is marginally detectable by the ongoing collaboration CELESTE.
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