A few multiplets that can be added to the SM contain a lightest neutral component which is automatically stable and provides allowed DM candidates with a non-standard phenomenology. Thanks to coannihilations, a successful thermal abundance is obtained for well defined DM masses. The best candidate seems to be a SU(2) L fermion quintuplet with mass 4.4 TeV, accompanied by a charged partner 166 MeV heavier with life-time 1.8 cm, that manifests at colliders as charged tracks disappearing in π ± with 97.7% branching ratio. The cross section for usual NC direct DM detection is σ SI = f 2 1.0·10−43 cm 2 where f ∼ 1 is a nucleon matrix element. We study prospects for CC direct detection and for indirect detection.

We calculate the antiproton flux due to relic neutralino annihilations, in a two-dimensional diffusion model compatible with stable and radioactive cosmic ray nuclei. We find that the uncertainty in the primary flux induced by the propagation parameters alone is about two orders of magnitude at low energies, and it is mainly determined by the lack of knowledge on the thickness of the diffusive halo. On the contrary, different dark matter density profiles do not significantly alter the flux: a NFW distribution produces fluxes which are at most 20% higher than an isothermal sphere. The most conservative choice for propagation parameters and dark matter distribution normalization, together with current data on cosmic antiprotons, cannot lead to any definitive constraint on the supersymmetric parameter space, neither in a low-energy effective MSSM, or in a minimal SUGRA scheme. However, if the best choice for propagation parameters -corresponding to a diffusive halo of L = 4 kpc -is adopted, some supersymmetric configurations with the neutralino mass mχ < ∼ 100 GeV should be considered as excluded. An enhancement flux factor -due for instance to a clumpy dark halo or to a higher local dark matter density -would imply a more severe cut on the supersymmetric parameters.PACS numbers: 95.35.+d,98.35.Gi,98.35.Pr,98.70.Sa,11.30.Pb,12.60.Jv,95.30.Cq

Once the energy spectrum of the secondary component is well understood, measurements of the antiproton cosmic-ray flux at the Earth will be a powerful way to indirectly probe for the existence of supersymmetric relics in the galactic halo. Unfortunately, it is still spoilt by considerable theoretical uncertainties. As shown in this work, searches for low-energy antideuterons appear in the mean time as a plausible alternative, worth being explored. Above a few GeV/n, a dozen spallation antideuterons should be collected by the future AMS experiment on board ISSA. For energies less than ∼ 3 GeV/n, theD spallation component becomes negligible and may be supplanted by a potential supersymmetric signal. If a few low-energy antideuterons are discovered, this should be seriously taken as a clue for the existence of massive neutralinos in the Milky Way.

The predictions of our previous analysis about possible low-mass (mχ < ∼ 50 GeV) relic neutralinos are discussed in the light of some recent results from WIMP direct detection experiments. It is proved that these light neutralinos are quite compatible with the new annual-modulation data of the DAMA Collaboration; our theoretical predictions are also compared with the upper bounds of the CDMS and EDELWEISS Collaborations.PACS numbers: 95.35.+d,11.30.Pb,12.60.Jv,95.30.Cq Searches for neutralinos at colliders have not yet reached the sensitivity required to place a direct lower bound on the neutralino mass m χ . The commonly quoted and employed bound m χ > ∼ 50 GeV is derived from the lower bound on the chargino mass determined at LEP2 (m ± χ > ∼ 100 GeV) under the assumption that the U (1) and SU (2) gaugino masses M 1 and M 2 satisfy the standard relationship M 1 ≃ 1 2 M 2 at the electroweak scale. This hypothesis is a consequence of the assumption that these mass parameters have a common value at the grand unification (GUT) scale.In supersymmetric models with R-parity conservation and no gaugino-unification assumption at the GUT scale, an absolute lower limit on m χ cannot be derived from the lower bound on the chargino mass. Instead, it may be established by applying the upper bound on the Cold Dark Matter (CDM) content in the Universe, Ω CDM ≡ ρ CDM /ρ c , in combination with constraints imposed on the Higgs and supersymmetric parameters by measurements at colliders and other precision experiments (muon g − 2, BR(b → s + γ)). This point was discussed in Refs. [1,2], where a lower bound on the neutralino mass of about 6 GeV was established as a consequence of the recent 2σ C.L. (2) is a consequence the fact that the detection rate has a lower bound induced by the upper limit on Ω CDM h 2 .Recalling that, for neutralino-matter interactions, coherent effects systematically dominate over spindependent ones, the aforementioned properties (1)-(2) are conveniently displayed in terms of the quantity ξσ is the neutralino-nucleon scalar cross-section and ξ is a rescaling factor between the neutralino local matter density ρ χ and the total local dark matter density ρ 0 : ξ ≡ ρ χ /ρ 0 . Following a standard assumption, ξ may be taken asThe supersymmetric model considered in the present paper is an effMSSM scheme at the electroweak scale, with the following independent parameters: M 2 , µ, tan β, m A , mq, ml, A and R ≡ M 1 /M 2 . Notations are as follows: tan β the ratio of the two Higgs v.e.v.'s: tan β ≡< H 0 2 >/< H 0 1 >, µ is the Higgs mixing mass parameter, m A the mass of the CP-odd neutral Higgs boson, mq is a soft-mass common to all squarks, ml is a soft-mass common to all sleptons, A is a common dimensionless trilinear parameter for the third family, Ab = At ≡ Amq and Aτ ≡ Aml (the trilinear parameters for the other families being set equal to zero). Since we are here interested in light neutralinos, we consider values of R lower than its standard value: R GUT ≃ 0.5; for definiteness, we take R in the range: ...