The Identification of Dark Matter

The following sections are included:

• Preface

• Committees

• Contents

A brief overview is given of the mechanisms that generate CMB anisotropies, concentrating on the model degeneracies intrinsic to CMB data alone. These degeneracies are broken by the addition of LSS information, resulting in a well-specified model. Spatial curvature must be low, with |Ω – 1| < 0.05 at 95% confidence. If the universe is exactly flat, the CMB power spectrum measures the combination Ω_mh³ = 0.092 ± 6%. Adding LSS data also breaks this degeneracy, requiring Ω_m = 0.26 ± 15% and h = 0.71 ± 6%. The preferred model is scalar-dominated, although a substantial tensor contribution is hard to rule out without a precise measurement of the amplitude of mass fluctuations. The prospects for further tests and refinements of this picture are discussed.

Observational evidence suggests that our universe is presently dominated by a dark energy component and undergoing accelerated expansion. The idea of the transplanckian dark energy (TDE) is based on the freeze-out mechanism of the ultralow frequency modes, ω(k) of very short distances, by the expansion of the background universe, ω(k) ≤ H. We then derive the equation of state for the TDE model, which has the distinctive feature of being continually time-dependent. The explanation of the coincidence puzzle relies entirely on the intrinsic time-evolution of the TDE equation of state.

Despite their many attractive cosmological features, quintessence models face two major naturalness problems: 1. They do not yet explain present-day cosmic acceleration in a generic way, using only attractor solutions. 2. They are difficult to obtain within realistic microscopic theories, due the incredibly small mass which is required by the quintessence field. This article summarizes both of these difficulties, and briefly outlines a recent proposal for circumventing the second of them within a brane-world context. This proposal leads to a broader class of dynamics for the quintessence field than is normally considered, in which the its couplings slowly run (or: ‘walk’) over cosmological time scales. The walking of the quintessence couplings may help produce acceptable cosmologies using attractor solutions.

We discuss a modification to the Friedmann Robertson Walker equation in which the universe is flat, matter dominated, and accelerating. The Friedmann equation is generically modified in braneworld scenarios. An additional term, which contains only matter or radiation (no vacuum contribution), becomes the dominant driver of expansion at a late epoch of the universe. During the epoch when the new term dominates, the universe accelerates; we call this period of acceleration the Cardassian era. The universe can be flat and yet consist of only matter and radiation, and still be compatible with observations. The energy density required to close the universe is much smaller than in a standard cosmology, so that matter can be sufficient to provide a flat geometry. The new term required may arise, e.g., as a consequence of our observable universe living as a 3-dimensional brane in a higher dimensional universe. The Cardassian model survives several observational tests, including the cosmic background radiation, the age of the universe, the cluster baryon fraction, and structure formation.

Let our Universe resemble a 4-dim bubble, floating in a flat (or AdS) 5-dim background, but insist on its evolution being governed by the standard Einstein-Hilbert action. The conserved bulk energy then parameterizes an intriguing deviation from general relativity with an essential built-in Einstein limit. Even an apparently ‘empty’ bubble Universe is effectively infested by a dark (= beyond Einstein) component. In particular, the geodetic evolution of a Λ-dominated toy Universe, absolutely free of genuine matter, gets translated into a specific FRW cosmology which is barely distinguishable from ΛCDM. A more realistic model presents a dark dominated era which bridges past (radiation/baryon dominated) and future (Λ-dominated) Einstein regimes. To prove the clumpiness property of our unified dark component, we have derived the geodesic brane analog of Schwarzschild solution. It is characterized by (i) Dark cosmological background, (ii) Newtonian limit, and quite serendipitously allows for (iii) Non-singular dusty core.

The lightest supersymmetric particle, most likely the lightest neutralino, is one of the most prominent particle candidates for cold dark matter (CDM). We show that the primordial spectrum of density fluctuations in neutralino CDM has a sharp cut-off, induced by two different damping mechanisms. During the kinetic decoupling of neutralinos, non-equilibrium processes constitute viscosity effects, which damp or even absorb density perturbations in CDM. After the last scattering of neutralinos, free streaming induces neutralino flows from overdense to underdense regions of space. Both damping mechanisms together define a minimal mass scale for perturbations in neutralino CDM, before the inhomogeneities enter the nonlinear epoch of structure formation. We find that the very first gravitationally bound neutralino clouds ought to have masses above 10⁻⁶M_⊙, which is six orders of magnitude above the mass of possible axion miniclusters.

The distance-redshift relation observed for supernovae has led to the discovery that the expansion of the universe is accelerating. A next generation experiment, the Supernova/Acceleration Probe (SNAP), can investigate the nature of the dark energy responsible, determining its energy density contribution and equation of state. In addition, indications of time variation in the equation of state could provide critical clues to the underlying fundamental physics.

There have been proposals that primordial black hole relics are the sources for dark matter. In the absence of a solid theoretical foundation, such notions remain vague. We argue that the generalized uncertainty principle (GUP) may prevent black holes from total evaporation in a similar way that the standard uncertainty principle prevents the hydrogen atom from total collapse. Specifically we invoke the GUP to obtain a modified Hawking temperature, which indicates that there should exist non-radiating remnants (BHR) of about Planck mass and Planck size. Combining this argument with the hybrid inflation model, we show that primordial BHRs can be the primary source of dark matter. We discuss the post-inflation cosmology and possible signatures associated with this notion.

Topological structures of gravitational vacuum which could be produced in the result of the first relativistic phase transition or in the result of defect creation of the Universe from “nothing” are discussed. The concrete physical meaning is imparted to the parametrizational noninvariant members of Wheeler -DeWitt equation which may be considered as vacuum topological defects of different dimensions (worm-holes, micromembranes, microstrings and monopoles). After Universe inflation defects smoothed, stretches and broken up. They must be isotropic distributed on background of the expanding Universe. The part of them has survived and now they are perceiving as the structures of Λ -term, quintessence and unclustered dark matter. Mathematical illustration of these processes may be spontaneous breaking of global Lorentz-invariance of quantum geometrodynamics equations.

I discuss anew how arguments about the internal dynamics of galactic disks set constraints on the otherwise ambiguous decomposition of the rotation curves of spiral galaxies into the contributions by the various constituents of the galaxies. Analyzing the two sample galaxies NGC3198 and NGC2985 I conclude from the multiplicities of the spiral arms and the values of the Q disk stability parameters that the disks of both galaxies are ‘maximum disks’.

Weakly Interacting Massive Particle (WIMP) direct detection experiments are closing in on the region of parameter space where neutralinos may constitute the Galactic halo dark matter. Numerical simulations and observations of galaxy halos indicate that the standard Maxwellian halo model is likely to be a poor approximation to the dark matter distribution. We examine how halo models with triaxiality and/or velocity anisotropy affect exclusion limits, before discussing the consequences of the possible survival of small scale clumps.

Terrestrial WIMP and axion detection experiments probe the local velocity-space distribution of dark matter particles. We review the theoretical approaches that have been used to model this distribution. We then describe a new method, to be combined with standard cosmological N-body simulations, that allows one to extract a local velocity-space distribution function in exquisite detail. Preliminary results and implications for direct detection experiments are discussed.

Some recent determinations have yielded a lower amplitude for the matter power spectrum, as parametrised through σ₈, the linear theory rms fractional density perturbations in spheres of radius 8h⁻¹Mpc, than had previously been inferred. The impact upon predicted dark matter halo properties of this smoother mass distribution is considered, with particular reference to the Milky Way. A rough calculation of the effect of baryonic contraction is also included. It is found that the uncertainties are sufficient to preclude the rejection of CDM as a viable model for the Milky Way halo. This conclusion is reached using either the observed dark matter density at the Solar radius or the integrated mass within the Solar radius.

Annihilation radiation from supersymmetric particles at the Galactic center could be greatly enhanced if the dark matter density is peaked around the supermassive black hole. Arguments for and against the existence of density spikes are reviewed. Spikes are destroyed during mergers, and there is strong evidence for this effect in stellar density profiles. The dark matter spike at the Galactic center probably suffered this fate.

The dynamics of charge particles and solitary waves in Newtonian Dark Matter (NDM) is discussed. Here NDM is considered as subbarionic gaseous type compressible medium with a nonlinear dispersion. The particle-like solitons with concentrated mass and charge in their centers present charge particle dynamic description. The charge particles with high (supercritical) velocity are good enough model for ultra-high energy cosmic rays. Another example presents classic solitary waves in NDM medium which can simulate gamma-ray bursts and their afterglow.

We present a new analysis of the direct detection rates of the neutralino WIMP in the framework of the minimal supersymmetric standard model. We discuss the impact of the current bounds on the Higgs mass, BR(b → sγ), (g − 2)_μ, as well as that of the cosmological range for the neutralino relic abundance. We derive upper and lower limits on the detection rates and compare them with current and planned experimental searches.

We review the current status of the Brookhaven muon g - 2 experiment, and it's effects on the SUSY parameter space when combined with dark matter relic density bounds, b → sγ and Higgs mass constraints. If the 3σ deviation of g - 2 from the Standard Model value is correct, these data constrain the mSUGRA parameter space strongly, i.e. 300 GeV ≲ m_1/2 ≲ 850 GeV, and m₀ ( at fixed tan β, A₀) is tightly constrained (except at very large tan β). Dark matter detection cross sections lie within the range accessible to future planned experiments. A non-universal gluino soft breaking mass however can greatly reduce the lower bound on m_1/2 (arising from the b → sγ constraint) allowing for relatively light neutralinos, while non-universal Higgs H₂ mass can lead to new regions of allowed relic density where the detection cross sections can be increased by a factor of 10 or more.

A wide range of supersymmetric searches has been performed at LEP. The negative outcome of those searches has been translated into indirect constraints on the lightest neutralino, , a good supersymmetric candidate for the cold dark matter. After presenting the LEP experimental environment, the lower mass limit within different theoretical assumptions will be reviewed

The status of the Tevatron and the CDF and DØ experiments is reviewed and recent results from Run I SUSY searches are presented.

The considerable centre-of-mass energy and luminosity provided by the Large Hadron Collider will ensure a discovery reach for new particles which extends well into the multi-TeV region. ATLAS and CMS have carried out many studies of the implications of this capability for Beyond the Standard Model physics, focussing in particular on supersymmetric models. In this paper we summarise some key results of these studies.

This article reviews the nature and distribution of baryonic dark matter in galaxies, with a particular emphasis on the Milky Way. The microlensing experiments towards the Large Magellanic Clouds, the Andromeda Galaxy and the bulge provide evidence on the characteristic mass and abundance of baryonic dark matter, as do direct searches for local counterparts of dark halo populations.

The nature of the dark matter in the halo of our Galaxy is still largely unknown. The microlensing events found so far towards the Large Magellanic Cloud suggest that at most 20% of the halo dark matter is in the form of MACHOs (Massive Astrophysical Compact Halo Objects) and that they probably belong to different intervening populations. The halo dark matter could also, at least partially, consist of cold molecular clouds (mainly H₂).

Brown dwarfs are now being discovered in significant numbers which means that at last it is possible to be quantitative about their number density and thus their contribution to the stellar neighbourhood. Overall the emerging picture is one of rising mass function into the brown dwarf regime though with a total brown dwarf mass contribution of around 10 percent that due to stars. Contrary to earlier expectations, these stars too small to burn nuclear fuel, do not contribute significantly to our Galaxy's missing mass. However, their properties are more complex than expected and thus there are considerable uncertainties to overcome before a robust determination of the brown dwarf mass function is possible.

The variability of quasars has long held the promise of shedding light on their detailed structure, and possibly other cosmosological phenonema. Different emission mechanisms lead to different patterns of variability in flux which are in principle easily distinguishable. Recent predictions for the expected spectrum of variations for various quasar models are now in such a form that they can be compared with the observed statistical properties of quasar light curves from large scale monitoring programmes. In this paper, we use the results of a long term monitoring programme of a large sample of quasars to distinguish between the various model predictions. The results appear to conclusively rule out models based on accretion disc instability or starburst, on the basis of both the shape and the timescale of the spectrum of fluctuations. However, predictions for the spectrum of fluctuations from gravitational microlensing by a population of compact bodies along the line of sight agree well with the observed variation. These sub-stellar mass bodies would be sufficient to make up the dark matter.

The EROS2 microlensing survey searches for massive compact halo objects towards the Large Magellanic Cloud (LMC) and the Small Magellanic Cloud (SMC). New results towards the SMC improve the previous constraints on the baryonic dark halo. Halo white dwarfs, a popular baryonic dark matter candidate, were searched for directly with a separate high proper motion survey with an area of ~ 380°². Strong limits are set on a possible protogalactic white dwarf population.

I report on recent results from the POINT-AGAPE pixel-lensing experiment, which is engaged in a search towards the Andromeda galaxy (M31) for gravitational microlensing signatures from massive compact halo objects (Machos). An analysis of two years of data reveals over 360 light-curves compatible with microlensing. The third year of data, currently being analysed, will be crucial in determining how many of these candidates are long-period variables rather than microlensing. Within the dataset we have isolated a subset of four high signal-to-noise ratio, short duration events which are compelling microlensing candidates. The properties and possible origins of these events are discussed.

The properties of the neutralino as a candidate to provide the dark matter in the Universe are discussed taking into account the present experimental strategies for detecting WIMPs. The latest constraints coming from accelerator physics are taken into account, included the recent measurement of the muon anomalous magnetic moment.

Ranges of direct detection cross section are presented for the neutralino in the general MSSM and in the CMSSM. Current experimental sensitivity already allows one to exclude some otherwise allowed points in the MSSM, but it is still at least an order of magnitude away from the most likely values of the direct detection cross section predicted in the CMSSM. A new generation of detectors will be able to explore a large fraction of this range.

Dark matter searches using cryogenic detectors are summarized. Latest results show that detection sensitivities reached with cryogenic devices exceed those obtained with most conventional detectors. The most spectacular results are from CDMS and EDELWEISS, which are incompatible with the DAMA data.

Axion physics is briefly reviewed. Constraints from laboratory searches, astrophysics and cosmology require the axion mass to be in the range 10⁻⁶ ≲ m_a < 3 · 10⁻³eV. Near the lower end of this range, axions are all or a major component of the cold dark matter of the universe. The late infall of axions, and of any other cold dark matter particles, onto our galaxy produces streams and caustics in its halo. The outer caustics are topological spheres whereas the inner caustics are rings. The self-similar model of galactic halo formation predicts that the caustic ring radii a_n obey the approximate law a_n ~ 1/n. Evidence for this law has been found in a statistical study of 32 extended and well-measured external galactic rotation curves, and in the existence and distribution of sharp rises in the Milky Way rotation curve. Moreover, a triangular feature in the IRAS map of the Galactic plane is consistent with the imprint of a ring caustic upon the baryonic matter. Its position coincides with a rise in the rotation curve, the one nearest to us. These observations imply that the dark matter in our neighborhood is dominated by a single flow. Estimates of that flow's density and velocity vector are given.

There is mounting evidence for dark matter in the Universe and one of the favourite dark matter candidates is the neutralino, which naturally appears as the lightest supersymmetric particle (LSP) in many supersymmetric extensions of the standard model. The neutralino has the desired properties to be a good dark matter candidate and we will here review the different indirect searches for neutralino dark matter and discuss the implications on these from recent direct searches.

We investigate the prospects of detecting weakly interacting massive particle (WIMP) dark matter by measuring the contribution to the extragalactic gamma-ray radiation induced, in any dark matter halo and at all redshifts, by WIMP pair annihilations into high-energy photons. Such signal has a very striking spectral signature and is less sensitive than other proposed signals to details about the distribution of WIMPs in dark halos.

A fit to the present cosmic ray positron fraction can be considerably improved, if in addition to the positron production by nuclear interactions in the universe the possible contribution from supersymmetric dark matter annihilation is taken into account. We scan over the complete SUSY parameter space of the Constrained Minimal Supersymmetric Model (CMSSM) and find that in the acceptable regions the neutralino annihilation into quark pairs is the dominant channel with hard positrons emerging from the semileptonic decays of the B-mesons.

Hot dark matter, now ignored, could have had an appreciable effect on structure formation, even as a minor component. If the LSND results are correct, then in the 2+2 neutrino scheme the total neutrino mass would be about 1–2 eV (3–6% of critical mass), or even as much as 5 eV. That scheme, which requires a light sterile neutrino, has been discounted recently, but this view is based on incorrect assumptions. That there are only the three light active neutrinos is popular because of some success in fitting solar neutrino data. This may also be incorrect, since Cl and Ga solar neutrino data yield statistically compelling evidence for rotational modulations of the neutrino flux, indicating that Resonant-Spin-Flavor-Precession could be the process responsible. To that evidence, summarized here, is now added that from recently released Super-Kamiokande data.

The question of the nature of dark matter in the Universe remains one of the most outstanding unsolved problems in basic science. One of the best motivated particle physics candidates is the lightest supersymmetric particle, assumed to be the lightest neutralino. We here describe DarkSUSY, an advanced numerical FORTRAN package for supersymmetric dark matter calculations. With DarkSUSY one can: (i) compute masses and compositions of various supersymmetric particles; (ii) compute the relic density of the lightest neutralino, using accurate methods which include the effects of resonances, pair production thresholds and coannihilations; (iii) check accelerator bounds to identify allowed supersymmetric models; and (iv) obtain neutralino detection rates for a variety of detection methods, including direct detection and indirect detection through antiprotons, gamma-rays and positrons from the Galactic halo or neutrinos from the center of the Earth or the Sun.

The program micrOMEGAs that calculates the relic density of the lightest super-symmetric particle (LSP) in the MSSM is presented. The impact of coannihilation channels and of higher order corrections to Higgs widths is stressed. The dependence on the RGE code used to calculate the soft parameters is also discussed.

Core-collapse supernovae can be used to place limits on dark matter candidate particles, but the strength of these limits depends on the depth of our theoretical understanding of these astrophysical events. To date, limitations on computing power have prevented inclusion of all the physics that would constitute a realistic simulation. The TeraScale Supernova Initiative (TSI) will overcome these obstacles in the next few years, elucidating the explosion mechanism and other phenomena closely associated with the core collapse of massive stars.

The DAMA experiment at the Gran Sasso National Laboratories of the INFN is searching for rare processes deep underground by developing and using large mass highly radiopure scintillators. Several experimental set-ups have been realized and, in particular, the ≃ 100 kg NaI(Tl) and the ≃ 6.5 kg LXe set-ups. The ≃ 100 kg NaI(Tl) set-up is mainly devoted to investigations on the WIMP component in the galactic halo by means of the annual modulation signature. This paper briefly summarizes the activities of DAMA experiment and the next perspectives are briefly addressed.

The NaIAD experiment (Nal Advanced Detector) for WIMP dark matter search at Boulby mine (UK) is described. The detector consists of an array of independent encapsulated and unencapsulated NaI(Tl) crystals with high light yield and low background. Eight modules are currently collecting data. Data from four modules (10.6 kg×years exposure) have been analysed to set limits on the WIMP-nucleon spin-independent and spin-dependent cross-sections. Pulse shape analysis was applied to discriminate between nuclear recoil events, possibly caused by WIMP interactions and electron recoil events due to gamma background. New analysis techniques have been developed to reject PMT noise events from experimental data, which are expected to significantly improve the sensitivity of the experiment.

The latest results obtained with three heat-and-ionisation 320 g germanium bolometers are described. In the recoil energy range relevant for WIMP masses below 10 TeV/c², no nuclear recoils were observed in the fiducial volume of one of the detectors during an exposure of 7.4 kg days. This result is combined with the previous 2000 EDELWEISS data to derive limits for cross-section for spin-independent interaction of WIMPs and nucleon in the framework of the MSSM. These exclude at more than 99.8% CL a WIMP with a mass of 44 GeV/c² and a cross-section of 5.4×10⁻⁶ pb, as reported by the DAMA collaboration. A few Supersymmetric models are also excluded at 90% CL. The next step EDELWEISS II involves 28 germanium bolometers.

In early 2000 CDMS set the most competitive exclusion limit for scalar-interaction WIMPs at the Stanford Underground Facility (SUF). A new search (CDMS II) is now commencing at the Deep-site Soudan Facility.

Results from 75 days of data collected by the ZEPLIN I detector are presented. The detector, a 3.1kg liquid xenon target operated by the UKDMC at the Boulby mine, is described. Calibration techniques, efficiency calculations and the techniques used to remove background events are described, including the use of active turrets of liquid xenon to reject low energy events from the photomultipliers.

One IGEX ⁷⁶Ge double-beta decay detector is currently operating in the Canfranc Underground Laboratory in a search for dark matter WIMPs, through the Ge nuclear recoil produced by the WIMP elastic scattering. In this talk we report on the on-going efforts to understand and eventually reject the background at low energy. These efforts have led to the improvement of the neutron shielding and to partial reduction of the background, but still the remaining events are not totally identified. A tritium contamination or muon-induced neutrons are considered as possible sources, simulations and experimental test being still under progress. According to the success of this study we comment the prospects of the experiment as well as those of its future extension, the GEDEON dark matter experiment.

A status report on the CRESST (cryogenic rare event search with superconducting thermometers) experiment is given. Results obtained for phase I of the experiment using sapphire detectors are briefly reviewed. Subsequently, CRESST's recent activities are summarized, focusing on the preparation of CRESST phase II detector modules. These modules consist of a CaWO₄ cryogenic scintillator combined with a very sensitive cryogenic light detector. These new detectors exhibit a very good discrimination capability between electron- and nuclear recoils. Progress in the development of optimized phase II modules for CRESST will be presented.

WIMPs dark matter and double beta decays has been studied at OTO Cosmo Observatory. The observatory has great advantages of small cosmic ray flux, small neutron flux and small radon density. The recent status of WIMPs search by huge NaI (ELEGANT V), large CaF₂Eu) (ELEGANT VI) and high sesitive NaI detector are reported.

Tokyo group has performed first underground dark matter search experiment in 2001 through 2002 at Kamioka Observatory (2700m.w.e). The detector is eight LiF bolometers with total mass 168g aiming for the direct detection of WIMPs via spin-dependent interaction. With a total exposure of 4.1 kg·days, we derived the limits in the a_p – a_n (WIMP-nucleon couplings) plane and excluded a large part of the parameter space allowed by the UKDMC experiment.

The ORPHEUS detector consisting of 446 g of superconducting Sn granules with diameters of 28 and 36 μm has been operated continuously for two months at a temperature of 170 mK. The overall performance of the detector was according to expectations. The background rejection capability of the detector is currently under study.

The DRIFT-I detector is the first direction-sensitive WIMP dark matter detector currently running and gathering data underground. Motivations for developing a directional detector are briefly reviewed and the status of DRIFT-I is summarised.

We are preparing an experiment for dark matter(WIMP) search using CsI(Tℓ) crystal. The detection threshold of a large CsI(Tℓ) crystal coupled with green extended pmts was down to 2 keV, and the pulse shape discrimination power of the crystal shows better separation of nuclear recoil from background electron signals than NaI(Tℓ) . With these characteristics, CsI(Tℓ) is another good material for WIMP search experiment. The disadvantage of CsI(Tℓ) is the internal background from cesium and rubicium ratioisotopes. In this report, the methods to reduce these ratioisotopes is described, and a perspective for the experiment is presented.

The background spectra of CsI(Tℓ) crystal detectors in a prototype shield were obtained. The lowest background count rate of the test sample of crystals is measured to be 64.7 ± 5.1 counts/keV/kg/day in the energy range of 5-20 keV. Quantitative estimation of residual radioactive isotope in CsI(Tℓ) was made using the GEANT4 Monte Carlo simulation. Analysis results show that CsI(Tℓ) crystal could be a good candidate for direct detection of WIMPs when the contamination level of cesium radioisotopes is reduced to under a few mBq/kg.

The scintillation yields and decay shapes for recoil Xe-ions produced by WIMPs in liquid xenon have been considered. A rough calculation based on biexcitonic diffusion reaction mechanism gives the average energy to produce a vuv photon W_ph to be ~90 eV for 60 keV recoil Xe-ions.

We describe the construction status of ZEPLIN II detector, a 30-kg two-phase discriminating xenon detector to be installed in Boulby Mine, UK, for the direct detection of WIMP dark matter. Both scintillation and ionization will be measured in order to discriminate the radioactive background. ZEPLIN-II will have very high radioactive-background rejection efficiency. We will also discuss the study of a ton scale ZEPLIN IV. The ZEPLIN program is a collaborative work of UCLA, TAMU, UKMDMC, and Torino, Italy.

The current status of a development project focused on constructing a novel two-phase xenon detector to search for Dark Matter is given. The response to neutrons in terms of ionisation and scintillation has been observed. Decay times of the scintillation due to nuclear recoils have been measured.

In this paper we describe our recent results on the study of avalanche photodiodes for detection of scintillation of liquid xenon, namely measurements of very low intensity light pulses and the photodiode excess noise as a function of temperature. Some other aspects relevant to the use of liquid xenon scintillation for particle detection are also addressed. In particular, we refer our measurements of the refraction index and attenuation length of the liquid for the VUV light emitted by xenon, which were found to be 1.69±0.02 and 36.4±1.8 cm, respectively.

An optical model of a two-phase xenon chamber for direct calculation of light fluxes has been built up. A calculation method of photo multiplier tubes response at charged particle interacting in chamber was deduced. A method of 3D reconstruction of event coordinates was built and studied with use of this model.

The XMASS project utilizes ultrapure liquid xenon and aims to detect pp and ⁷Be solar neutrinos by means of ν+e scatterings. It also aims to detect dark matter and double beta decay. We studied the most suitable design of the detector for dark matter detection and found that a full photosensitive type detector is appropriate since it has an extremely low energy threshold.

Xenon targets are attracting a lot of attention for dark matter detectors as they offer a number of possible operational modes, with the potential for significant discrimination power between gamma-ray backgrounds and WIMP induced elastic nuclear recoils. This article summarises the world activity with xenon-based detectors, highlighting the key technological areas of interest, and looks at the future prospects offered by xenon.

The CAST experiment is being mounted at CERN. It will make use of a decommissioned LHC test magnet to look for solar axions through its conversion into photons inside the magnetic field. The magnet has a field of 9 Tesla and length of 10 m and is installed in a platform which allows to move it ±8° vertically and ±40° horizontally. According to these numbers we expect a sensitivity in axion-photon coupling g_aγγ ≲ 5 × 10⁻¹¹ GeV⁻¹ for m_a ≲ 10⁻² eV, and with a gas filled tube g_aγγ ≲ 10⁻¹⁰ GeV⁻¹ for m_a ≲ 2 eV.

I report on the status of the Axion Dark-Matter Experiment (ADMX), the microwave-cavity-based axion search underway at Lawrence Livermore National Laboratory. The ADMX collaboration includes LLNL, the University of Florida, and M.I.T., and has been in operation since February, 1996.

In the PVLAS apparatus a polarised laser beam is used to probe the structure of quantum vacuum when it is perturbed by an external magnetic field. The photon-photon scattering process, taking place in the field region, could result in the production of light scalar/pseudoscalar particles coupled to two photons thought to be dark matter candidates. The photon-photon scattering induces a change in the polarisation state of the laser beam, and can be detected by optical techniques. The PVLAS collaboration has been operating the apparatus for about two years, and the available sets of data show the presence of a signal believed to originate within the magnetic field region. Preliminary results from the data sets will be presented, along with a brief discussion.

The use of Micromegas in low background Astroparticle physics investigations is discussed. We report experimental results obtained with a CAST detector for the solar axion experiment. The good X-Y imaging properties of the detector have been evaluated in a low energy x-ray beam and the background rejection capability has been measured. An excellent performance of 2.5×10⁻⁶events/keV/cm²/s background rate was measured.

The prospects of using the same detector for reading out large volume TPCs, for low energy neutrino investigations (solar neutrino spectrum, neutrino oscillations, neutrino magnetic moment) is also discussed

Recent developments in underground science are reviewed. Recent efforts to built a deep multi-purpose underground laboratory in the U.S. to explore a wide range of science are summarized.

This summer the Canadian Government announced that it would support the expansion of the Sudbury Neutrino Observatory into an International Facility for Underground Science. This paper presents the current thinking on the facilities that will be available and an outline of the scientific objectives of the laboratory.

The current status of the Boulby Underground Laboratory is described, with particular attention paid to the recently expanded and upgraded facilities for future underground science studies.

Liquid and plastic scintillators are ubiquitous pieces of apparatus used in any physics laboratory, and especially in the subterranean laboratories of dark matter and neutrino research; this talk details some further uses to which we would like to put them. Specifically, dark matter experiments based on nuclear recoil must exclude neutron background arising from U/Th contamination and from muon interactions, both in the underground rock and in detector components. Neutron shielding is used in current experiments, but to reach lower sensitivity levels active neutron shielding is now being considered for future DRIFT and ZEPLIN detectors, in particular, using loaded scintillator surrounding the target. This work is applicable also to the proposed OMNIS supernova detector, in which the neutrino burst would be detected by nuclear excitation in a lead target with release of neutrons. This detects all neutrino flavours, and would provide information on many aspects of the core collapse process and neutrino masses and oscillations. Practical tests and simulations are in progress for both types of project at the Boulby Mine.

The CDMS II experiment deployed a set of 6 ZIP (Z-dependent Ionization and Phonon) detectors at the Stanford Underground Facility (SUF) shallow depth site in the fall of 2001. With a payload consisting of 4 Ge (250g ea.) and 2 Si (lOOg ea.) ZIPs, the run demonstrated the simultaneous operability of multiple ZIPs. Excellent discrimination between electron and nuclear recoil events of 99.99%, between 5–100 keV, was established in addition to rejecting over 90% of surface electron recoils, while establishing a recoil threshold down to 5 keV. This presentation will report on the performance of the ZIPs as well as the measured background rates at SUF, their last stop before being deployed at the deep site in Soudan.

Cosmic rauon induced neutrons are a major source of background for low count rate experiments like neutrino oscillation or dark matter searches. Especially at shallow sites these neutrons are the limiting factor for the ultimate sensitivity of the measurement. Measurements of the neutron rate and counter measures including active veto and passive shielding of the detector are discussed for two neutrino oscillation experiments at shallow sites: the KARMEN accelerator based experiment at RAL and the PALO VERDE reactor experiment.

In direct searches for WIMPs neutrons are a particularly important background source because they produce the same signature as the searched particles. This background neutrons will in turn limit the sensitivity of the experiments. Study on background neutrons in Gran Sasso underground laboratory and the relevance for CRESST phase II is discussed.

Protection against the neutron background will be one of the key issues for the next generation of Dark Matter Direct Detection experiments. We review and discuss critically the main contributions for the neutron background – neutrons from rock fission and alpha-n reactions, muon-induced neutron background, deep-inelastic interactions, internal U/Th contamination. We discuss the impact of these backgrounds for the EDELWEISS-II experiment, designed to reach a sensitivity of the order of 10⁻² event/kg/day, and for an experiment at the one-ton scale.

The neutron background at the underground laboratory at Boulby - a site for several dark matter experiments - is discussed. Special emphasis is put on the neutron background produced by cosmic-ray muons. The most recent versions of the muon propagation code MUSIC, and particle transport code FLUKA are used to evaluate muon and neutron fluxes. The results of simulations are compared with experimental data.

The High Energy Antimatter Telescope is a magnet spectrometer complemented by an array of particle detectors, flown on high altitude balloons. With it, we have measured the positron content of the cosmic-ray flux at energies between 1 and 50 GeV, and the antiproton content from 4 to 50 GeV. We have found both antiparticle species to be substantially in agreement with models of secondary antimatter production in interstellar collisions of hadronic cosmic rays. The positron measurements however seem to consistently indicate the possibility of a small primary antimatter component. Just such a contribution has been predicted to result from the annihilation of dark matter particles in the galactic halo. The HEAT measurements are described here, and their connection with SUSY dark matter is explored.

Using a new instrument, the HEAT collaboration has confirmed the excess of cosmic ray positrons that they first detected in 1994. We explore the possibility that this excess is due to the annihilation of neutralino dark matter in the galactic halo. We confirm that neutralino annihilation can produce enough positrons to make up the measured excess only if there is an additional enhancement to the signal. We quantify the ‘boost factor’ that is required in the signal for various models in the Minimal Supersymmetric Standard Model parameter space, and find that a boost factor ≥ 30 provides good fits to the HEAT data. Such an enhancement in the signal could arise if we live in a clumpy halo.

We review the prospects of detecting supersymmetric dark matter in the framework of the Constrained Minimal Supersymmetric Standard Model, and compare indirect with direct detection capabilities.

The indirect detection of annihilation products in cosmic rays offers an alternative way to search for dark matter particles candidates. Here we will see in particular that the study of the spectrum of antiproton and positrons offer good possibilities to perform this search and we will review our experimental effort in this direction.

This article gives a description of the AMS-02 detector, focussing on the objective of indirect searches for Dark Matter.

The H.E.S.S. sensitivity is presented for the first telescope already operating in Namibia and for the four telescopes of phase 1 that will take data in 2004. Located in the southern hemisphere at a latitude of 22 degrees, HESS can look at the galactic centre and many galactic sources. Its sensitivity to a point source at Zenith is 10⁻¹¹ cm².s⁻¹ for an integrated spectrum above a threshold of 150 GeV for the first telescope and 2×10⁻¹¹ cm².s⁻¹ above 80 GeV for four telescopes. We discuss the potential of HESS to detect γ-ray emission from neutralino annihilation at the galactic centre for several halos models and for the globular cluster Omega Centauri using a semi-analytical dynamical model. We scan supersymetric models in the CMSSM framework with the help of SUSPECT and DARKSUSY.

The results of dark matter searches with the MACRO experiment are reported. In particular indirect searches for WIMP's and direct searches for supermassive GUT magnetic monopoles are reported together with massive neutrino studies through the measurement of the oscillation induced anomalies in the atmospheric neutrino flux.

We present the results of indirect searches for Weakly Interacting Massive Particles (WIMPs) with the 1678 days Super-Kamiokande-I data using neutrino-induced upward through-going muons from the Sun, the core of the Earth, and the Galactic Center. No such excess was seen. We present flux limits on WIMP induced muon flux from the above objects and model-independent upper limits on WIMP-nucleon cross-section as a function of WIMP mass.

The ANTARES neutrino telescope will be deployed in the western Mediterranean Sea during 2003 and 2004. The expected sensitivity of this detector to neutrinos from neutralino annihilation in the Sun is discussed in the context of mSUGRA models and direct detection experiments.

I discuss the cosmological implications of neutrino mass including the cosmological relic density and dark matter, the galaxy structure limits on neutrino mass, nucleosynthesis, supernovae, cosmic rays and gamma ray bursts.

One of the most important tasks in neutrino physics is to determine the neutrino mass scale to distinguish between hierarchical and degenerate neutrino mass models and to clarify the role of neutrinos as dark matter particles in the universe. The current tritium β decay experiments at Mainz and Troitsk are reaching their sensitivity limit. The different options for a next generation direct neutrino mass experiment with sub-eV sensitivity are discussed. The KATRIN experiment, which will investigate the tritium β spectrum with a 1 eV resolution MAC-E-Filter, is being prepared to reach a sub-eV sensitivity.

The phenomenology of neutrino-mixing, neutrinoless double-beta decay and the connection to neutrino oscillations is reviewed. Recent values of the mixing angles from atmospheric and solar neutrino oscillation experiments are used to predict values of the effective Majorana mass of the electron neutrino. Prospective sensitivities of next generation experiments to constrain or measure the neutrino mass scale are discussed, as well as the possible impact of these experiments on neutrino dark matter.

With direct evidence for flavor transformation of electron neutrinos born in the Sun into active non-electron-type neutrinos detected at Earth, the Solar Neutrino Problem has taken a new perspective with new goals and challenges for the future of the field.

After neutrino oscillation discovery, search for Neutrinoless Double Beta Decay (0ν–DBD) represents the new frontier of neutrino physics, allowing in principle to fix the neutrino mass scale, the neutrino nature (Dirac or Majorana particle) and to reveal CP violation effects. In this paper, we introduce the main experimental approaches to this search and review the most sensitive present experiments, able to constrain the effective neutrino Majorana mass (〈m_ν〉) to a value lower than a few tenths of eV. Next-generation experiments are then overviewed, with a critical comparison between the claimed performance and the real results achieved so far in the corresponding smaller-scale searches. A positive result in case of inverse-hierarchy neutrino-mass spectrum looks within the reach of the most promising future detectors.

Double beta decay is indispensable to solve the question of the neutrino mass matrix together with ν oscillation experiments. Recent analysis of the most sensitive experiment since nine years - the HEIDELBERG-MOSCOW experiment in Gran-Sasso - yields a first indication for the neutrinoless decay mode. This result is the first evidence for lepton number violation and proves the neutrino to be a Majorana particle. We give the present status of the analysis in this report. It excludes several of the neutrino mass scenarios allowed from present neutrino oscillation experiments - only degenerate scenarios and those with inverse mass hierarchy survive. This result allows neutrinos to still play an important role as dark matter in the Universe. To improve the accuracy of the present result, considerably enlarged experiments are required, such as GENIUS. A GENIUS Test Facility has been funded and will come into operation by early 2003.

The MiniBooNE experiment has recently started a search for ν_μ → ν_e oscillations at Fermilab. MiniBooNE is designed to check the result of the LSND experiment which shows evidence for neutrino oscillations. The MiniBooNE neutrino source and detector are both now operational and data taking has begun. The MiniBooNE experiment is overviewed along with the expected sensitivity to neutrino oscillations and the current status.

Future long baseline neutrino oscillation (LBL) setups are discussed and the remarkable potential for very precise measurements of mass splittings, mixing angles, MSW effects, the sign of Δm² and leptonic CP violation is shown.

Major progress in the understanding of neutrino properties and of the sun has recently been achieved by experiments with solar and reactor neutrinos. The intention of this paper is to summarize the present status and outline possible future activities in this field.

Detection of the cosmic neutrino background may become possible through coherent interaction with levitated sub-micron granules, utilising refined optical or quantum measurement techniques. Solar neutrinos and WIMPs gain less from coherence but their higher momentum would give measurable recoil velocities in micron size granules. Development of this technique initially as a directional dark matter detector would provide an intermediate step towards future relic neutrino detection.

The current status and future prospects of non-cryogenic dark matter detectors is discussed. These include super-heated droplet experiments and high mass scintillator experiments. The status and future of directional dark matter detectors is also discussed with attention to the DRIFT experiment and the planned DRIFT II and DRIFT III experiments.

The new project GENIUS will cover a wide range of the parameter space of predictions of SUSY for neutralinos as cold dark matter. Further it has the potential to be a real-time detector for low-energy (pp and ⁷Be) solar neutrinos. A GENIUS Test Facility has been funded and will come into operation by early 2003.

The annual modulation of the recoil spectrum observed in an underground detector is well known as the main signature of a possible WIMP signal.

The GENIUS-TF experiment, under construction in the Gran Sasso National Laboratory, can search for the annual modulation of the Dark Matter signal using 40 kg of naked-Ge detectors in liquid nitrogen. The parameter range correspondent to the recent evidence for Cold Dark Matter observed by the DAMA experiment can be explored within a few years of measurement.

Improvements in cryogenic thermal detector performances have triggered new generation experiments based on this devices. MiBeta detector had shown, during the last five years, the potential of a large mass cryogenic detector for long running time, good energy resolution, low energy threshold and low radioactive background experiment. Starting from this point a new very large cryogenic detector was proposed: CUORE (Cryogenic Underground Observatory for Rare Events). CUORE will be a segmented detector made with 1000 crystals of TeO₂ of 5×5×5 cm³, for a total detector mass around 760 kg. Thanks to the high granularity a considerable improvement in background rejection can be reached using coincidence analysis between crystals. The main goal of CUORE will be the search of neutrinoless double beta decay of ¹³⁰Te but also other studies are possible; in particular dark matter and solar axion searches. To prove the feasibility of CUORE a pilot experiment named CUORICINO was proposed and also founded. The estimated sensitivities of CUORICDMO and CUORE for WIMPs searches is here reported.

MACHe3 (MAtrix of Cells of superfluid ³He) is a project of a new detector for direct Dark Matter (DM) search, using superfluid ³He as a sensitive medium. An experiment on a prototype cell has been performed and the first results reported here are encouraging to develop of a multicell prototype. In order to investigate the discovery potential of MACHe3, and its complementarity with other DM detectors, a phenomenological study done with the DarkSUSY code is shown.

The theory of the detection of neutral light bosons from the sun, using Bragg-coherent Primakoff conversion to photons, is reviewed. A technique for data analysis that allows the combination of the results of completely distinct single-crystal experiments is also reviewed. The purpose of the revival of this subject stems from the many large single crystal arrays now under development for Cold Dark Matter and Neutrinoless Double-Beta Decay.

The following sections are included:

• LIST OF PARTICIPANTS.