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: ...

The relic abundance and the scalar cross section off the nucleon for light neutralinos ͑of mass below about 45 GeV͒ are evaluated in an effective MSSM model without GUT-inspired relations among the gaugino masses. It is shown that these neutralinos may provide a sizable contribution to the matter density in the Universe and produce measurable effects in WIMP direct detection experiments. These properties are elucidated in terms of simple analytical arguments.

The DAMA/NaI Collaboration has observed a 4-σ C.L. model independent effect investigating the annual modulation signature in the counting rate of an NaI(Tl) set-up (total exposure of 57986 kg day) and the implications of this effect have been studied under different model-dependent assumptions. In this paper we extend one of the previous analyses, the case of a WIMP with a purely spin-independent coupling, by discussing in detail the implications on the results of the uncertainties on the dark matter galactic velocity distribution. We study in a systematic way possible departures from the isothermal sphere model, which is the parameterization usually adopted to describe the halo. We specifically consider modifications arising from various matter density profiles, effects due to anisotropies of the velocity dispersion tensor and rotation of the galactic halo. The hypothesis of WIMP annual modulation, already favoured in the previous analysis using an isothermal sphere, is confirmed in all the investigated scenarios, and the effects of the different halo models on the determination of the allowed maximum-likelihood region in the WIMP mass and WIMP-nucleon cross-section are derived and discussed.

We discuss the gamma-ray signal from dark matter annihilation in our Galaxy and in external objects, namely, the Large Magellanic Cloud, the Andromeda Galaxy (M31), and M87. We derive predictions for the fluxes in a low energy realization of the minimal supersymmetric standard model and compare them with current data from EGRET, CANGAROO-II, and HEGRA and with the capabilities of new-generation satellite-borne experiments, like GLAST, and ground-based Č erenkov telescopes, likeVERITAS. We find fluxes below the level required to explain the possible indications of a -ray excess shown by CANGAROO-II (toward the galactic center) and HEGRA (from M87). As far as future experiments are concerned, we show that only the signal from the galactic center could be accessible to both satellite-borne experiments and to atmospheric Č erenkov telescopes (ACTs), even though this requires very steep dark matter density profiles.

We discuss the effect induced on the neutralino-nucleon cross-section by the present uncertainties in the values of the quark masses and of the quark scalar densities in the nucleon. We examine the implications of this aspect on the determination of the neutralino cosmological properties, as derived from measurements of WIMP direct detection. We show that, within current theoretical uncertainties, the DAMA annual modulation data are compatible with a neutralino as a major dark matter component, to an extent which is even larger than the one previously derived. We also comment on implications of the mentioned uncertainties for experiments of indirect dark matter detection. *