The Identification of Dark Matter

PREFACE.

CONTENTS.

We examine the question of whether neutralinos produced at the LHC can be shown to be the particles making up the astronomically observed dark matter. If the WIMP alllowed region lies in the SUGRA coannihilation region, then a strong signal for this would be the unexpected near degeneracy of the stau and neutralino i.e., a mass difference ΔM ≃ (5 - 15) GeV. For the mSUGRA model we show such a small mass difference can be measured at the LHC using the signal . Two observables, opposite sign minus like sign pairs and the peak of the ττ mass distribution allows the simultaneous determination of ΔM to 15% and the gluino mass to be 6% at the benchmark point of , A₀ = 0, μ > 0 with 30 fb^-1. With 10 fb^-1, ΔM can be determined to 22% and one can probe the parameter space up to m_1/2 = 700 GeV with 100 fb^-1.

We review the various methods to search for dark matter particles based on the results from the recent symposium at Marina Del Rey [1]. At present, the most promising methods are: (a) Direct searches with earth-bound detectors made of Ge, Xe, Ar, etc. (b) Search for Gamma Rays from dark matter annihilation in the local galaxy. We note there is progress on (a) to date, the expectation for the current generation of detectors CDMS II, Edelweiss II, ZEPLIN II, WARP etc. and hopes for future one ton detectors. In the case of (b) the detection of Dark Matter Gamma Rays will depend on the clumping of Dark Matter in the Galaxy and Backgrounds. We will discuss this. We also discuss very briefly warm dark matter.

A brief review is given of dark matter in SUGRA, strings and branes. For SUGRA models the implications of Yukawa coupling unification on dark matter are discussed in the light of g - 2 and b → sγ constraints. A brief discussion is given of the dark matter in orbifold string compactifications under constraints of modular invariance and radiative breaking of the electroweak symmetry. Finally a new candidate for dark matter - an extra-weakly interacting massive particle or an XWIMP- is discussed. Such dark matter can arise in a wide class of models, including the Stueckelberg extensions of MSSM, in U(1) extensions of MSSM with off diagonal kinetic energy, and possibly in a wider class of models which may have a string/D-brane origin. Satisfaction of the relic density of XWIMPs consistent with WMAP is also discussed.

A wide range of techniques have been developed to search for particle dark matter, including direct detection, indirect detection, and collider searches. The prospects for the detection of neutralino dark matter is quite promising for each of these three very different methods. Looking ahead to a time in which these techniques have successfully detected neutralino dark matter, we explore the ability of these observations to determine the parameters of supersymmetry. In particular, we focus on the ability of direct and indirect detection techniques to measure the parameters μ and m_A. We find that μ can be much more tightly constrained if astrophysical measurements are considered than by LHC data alone. In supersymmetric models within the A-funnel region of parameter space, we find that astrophysical measurements can determine m_A to roughly ±100 GeV precision.

The diffuse galactic EGRET gamma ray data show a clear excess for energies above 1 GeV in comparison with the expectations from conventional galactic models. This excess shows all the features expected from Dark Matter WIMP Annihilation: a)it is present and has the same spectrum in all sky directions, not just in the galactic plane, as expected for WIMP annihilation b) it shows an interesting substructure in the form of a doughnut shaped ring at 14 kpc from the centre of the galaxy, where a ring of stars indicated the probable infall of a dwarf galaxy. From the spectral shape of the excess the WIMP mass is estimated to be between 50 and 100 GeV, while from the intensity the halo profile is reconstructed, which is shown to explain the peculiar change of slope in the rotation curve at about 11 kpc (due to the ring of DM at 14 kpc).

Recently it was claimed by Bergström et al. that the DM interpretation of the EGRET gamma ray excess is excluded by the antiproton fluxes, since in their propagation model with isotropic diffusion the flux of antiprotons would be far beyond the observed flux. However, the propagation can be largely anisotropic, because of the convection of particles perpendicular to the disc and inhomogeneities in the local environment. It is shown that anisotropic propagation can reduce the antiproton yield by an order of magnitude, while still being consistent with the B/C ratio. Therefore it is hard to use antiprotons to search for light DM particles, which yield a similar antiproton spectrum as the background, but the antiprotons are a perfect means to tune the many degenerate parameters in the propagation models.

EDELWEISS is an experiment searching for dark matter WIMPs (weakly interacting massive particles) by measuring the heat and ionisation signals of low temperature germanium detectors. Following the successful conclusion of the first phase of EDELWEISS in the summer of 2003, involving a total of 1 kg of detector mass, phase II of the experiment was set-up in the Modane underground laboratory (LSM) and is now undergoing commissioning runs. It will operate 9 kg of detectors in a first step and 40 kg ultimately. A short summary of the results and conclusions from EDELWEISS I data and an update on the status of EDELWEISS II will be given in this article.

The XENON experiment aims at the direct detection of dark matter in the form of Weakly Interacting Massive Particles (WIMPs) via their elastic scattering off Xe nuclei. The final detector will have a fiducial mass of 1000 kg, distributed in 10 independent liquid xenon time projection chambers (TPCs). Such an experiment will be able to probe the lowest interaction cross-section predicted by SUSY models. The TPCs are operated in dual (liquid/gas) phase, to allow a measurement of nuclear recoils down to < 10 keV energy, via simultaneous detection of the ionization, through secondary scintillation in the gas, and primary scintillation in the liquid. The distinct ratio of primary to secondary scintillation for nuclear recoils from WIMPs (or neutrons), and for electron recoils from background, is used for the event-by-event discrimination. As part of the R&D phase, we built a first XENON module (XENON10) with 15 kg fiducial mass and installed it underground, at the Laboratori Nazionali del Gran Sasso (LNGS), on March 2006. XENON10 has accumulated an exposure of more than 30 live days, operating with quite stable condition. A preliminary analysis of the background data is presented here.

This paper sets out to measure the timescale of quasar variability with a view to new understanding of the size of accretion discs in active galactic nuclei. We combine data from two large scale monitoring programmes to obtain Fourier power spectra of light curves covering nearly three orders of magnitude in frequency in blue and red passbands. If the variations are interpreted as due to gravitational microlensing, then timescale measurements in the observer's frame imply a minimum mass for the microlensing bodies of around 0.4M_⊙.

The event rates for direct cold dark matter detection, both directional and non directional, are presented using a velocity distribution function obtained by considering a coupling between dark matter and dark energy. The magnitude of the effect depends on the strength κ of this new interaction relative to gravity. The resulting isothermal velocity distribution for dark matter in galaxy halos is still Maxwell-Boltzmann (M-B), but the characteristic velocity and the escape velocity are increased by . We adopt a phenomenological approach and consider values of κ near unity. The phenomenological implications of such a coupling are discussed.

We outline the WIMP dark matter parameter space in the Constrained MSSM by performing a comprehensive statistical analysis that compares with experimental data predicted superpartner masses and other collider observables as well as a cold dark matter abundance. We find that for direct WIMP detection (with details slightly dependent on the assumptions made). We conclude that most of the 95% probability region for the cross section will be explored by future one–tonne detectors, that will therefore cover most of the currently favoured region of parameter space.

This paper discusses the possibility that the cold dark matter may comprise dark baryons or primordial black holes as well as WIMPs. Some baryons are certainly dark and, although the most conventional repository for them would be hot or warm gas, they could also be contained in cold clouds or stellar remnants. Primordial black holes could provide dark matter if they are either too large to have evaporated or the stable relics of evaporating ones. All such objects would cluster inside halos, along with WIMPs, but if they were pregalactic, there would also be an intergalactic distribution of them. The term MACCHIO is introduced as a useful generalization of MACHO. There is no conclusive evidence for MACCHIOs but they could be of astrophysical interest even if their cosmological density is low.

The halo of the Miky Way might contain numerous and dense substructures inside which the putative weakly interacting massive particles (suggested as the main constituent of the astronomical dark matter) would produce a stronger annihilation signal than in the smooth regions. The closer the nearest clump, the larger the positron and antiproton cosmic ray fluxes at the Earth. But the actual distribution of these substructures is not known. The predictions on the antimatter yields at the Earth are therefore affected by a kind of cosmic variance whose analysis is the subject of this contribution. The statistical tools to achieve that goal are presented and Monte Carlo simulations are compared to analytic results.

The H.E.S.S. (High Energy Stereoscopic System) array of imaging atmospheric Cherenkov telescopes is designed to detect very high energy (E_γ>100GeV) γ-rays in the TeV range. A strong signal from the high energy source HESS J1745-290 has been detected in the direction of the Galactic Center. Constraints have been derived on a possible component due to dark matter particles annihilation. Diffuse γ-ray emission has been highlighted along the Galactic plane. Prospects of detection from Sagittarius Dwarf galaxy scheduled for observations will be discussed.

It is described the distribution of small-scale dark matter (DM) clumps in the Galactic halo. These clumps are efficiently destructed by tidal forces at early stages of structure formation starting from time of clump detachment from the expansion of the Universe. Only a small fraction of these clumps survives the stage of hierarchical clustering. The survived clumps can be further destructed in the Galaxy by tidal interactions with stars in the Galactic bulge, disk and halo. It is shown that collective gravitational field of the Galactic disc provides the dominant contribution to the destruction of small-scale clumps. The resulting enhancement (boost factor) of annihilation signal due to the halo clumpiness strongly depends on the primordial perturbation spectrum and varies in the range 10-100.

We present an overview of work on the merging cluster system 1E0657-56, commonly known as the "bullet" cluster. This system is one of only two known supersonic cluster mergers, and its unique properties enable fundamental constraints on the nature of dark matter. In a series of papers our group has used this system to demonstrate the existence of dark matter and place upper limits on the dark matter self-interaction cross section. In this proceedings we summarize these findings and discuss ongoing work to improve these constraints and quantify the impact of a supersonic merger on cluster galaxy evolution.

We present the history of the ZEPLIN two-phase concept and the early research and development for this detector. ZEPLIN II is now taking data at Boulby. ZEPLIN IV, a one-ton detector, is pre-approved for SNOLAB. We present the argument that a Liquid Xenon detector is crucial to discover and prove the existence of SUSY dark matter and the progress with ZEPLIN II and ZEPLIN IV.

PICASSO (Project in Canada to Search for Supersymmetric Objects) is entering its second experimental phase. A new setup has been installed underground at SNOLAB which will have a total of 2.5kg of active mass. For this a new detector with new purification techniques, new environmental control system and a new data acquisition have been developed. Data taking with the first new detectors has started at the time of the IDM 2006 conference.

The DAMA/NaI experiment (≃ 100 kg highly radiopure NaI(Tl)) at the Gran Sasso National Laboratory of the I.N.F.N. has pointed out - by a model independent approach - the presence of Dark Matter particles in the galactic halo at 6.3 σ C.L. with an exposure larger than 10⁵ kg × day collected over seven annual cycles. Several corollary model dependent quests for the candidate particle have also been carried out; others (of the many possible) are in progress. At present the second generation DAMA/LIBRA set-up (≃ 250 kg highly radiopure NaI(Tl)) is in data taking deep underground. A 3-rd generation R&D towards a possible 1 ton set-up, we proposed in 1996, is also in progress. Many searches for other rare processes have been and are under investigation as well.

The size and time of formation of the first gravitationally bound objects in the Universe is set by the microphysical properties of the dark matter. It is argued that observations seem to favour cold and thermal candidates for the main contribution to the dark matter. For that type of dark matter, the size and time of formation of the first halos is determined by the elastic cross sections and mass of the CDM particles. Consequently, the astrophysics of CDM might allow us to measure some of the fundamental parameters of CDM particles. Essential for observations is the survival rate and spatial distribution of the very first objetcs, which are currently under debate.

In this talk, I present the possibility of gravitino dark matter in the framework of the Constrained MSSM. Additionally we find the prospects of the gravitino for the implication on the vacuum structure of our universe and the solutions to the cosmic lithium problems.

The nature of Dark Matter is still elusive to the ongoing experimental search. We discuss some astrophysical techniques to search for the nature of DM through a multi-frequency analysis of cosmic structures on large scales, from dwarf galaxies to galaxy clusters.

The project of a micro-TPC matrix of chambers of ³He for direct detection of non-baryonic dark matter is outlined. The privileged properties of ³He are highlighted. The double detection (ionization - projection of tracks) will assure the electron-recoil discrimination. The complementarity of MIMAC-He3 for supersymmetric dark matter search with respect to other experiments is illustrated. The modular character of the detector allows to have different gases to get A-dependence. The pressure degreee of freedom gives the possibility to work at high and low pressure. The low pressure regime gives the possibility to get the directionality of the tracks. The first measurements of ionization at very few keVs for ³He in ⁴He gas are described.

The AMS-02 (Alpha Magnetic Spectrometer) detector will operate on the International Space Station performing spectroscopy of cosmic rays searching for dark matter, trying to identify the products of the annihilation of WIMP candidates such as neutralinos.

The annihilation of a neutralino of a few hundred GeV mass could produce an excess in the 10–300 GeV region of the cosmic rays positron spectrum. With the joint use of a Transition Radiation Detector (TRD) and of an electromagnetic calorimeter, providing an overall 10⁶ rejection factor for protons, AMS can detect a positron with a 90% efficiency.

The techniques used to achieve the physical and technological goals, together with the current status of the detector, will be discussed.

CRESST II is a WIMP search experiment using cryogenic detectors to detect heat and scintillation signals in CaWO₄ crystals simultaneously. Competitive limits on the coherent WIMP-nucleon scattering cross section and other results from runs from the upgrade to CRESST II are shown. New features and upgrades installed on the CRESST II setup are described and the status of the experiment is presented.

We describe the Argon Dark Matter (ArDM) experiment. It consists on a one-ton liquid argon detector able to read independently ionization charge and scintillation light. This device has been optimized to perform a direct search for Weakly Interacting Massive Particles (WIMPs).

The liquid Xenon set-up of the DAMA project (DAMA/LXe) is a low background experiment located deep underground at LNGS. It is in operation since time and has been uograded several times. It can be filled with Kr-free Xenon enriched either in ¹²⁹Xe at 99.5% or in ¹³⁶Xe at 68.8%. This set-up has already given several competitive results investigating various kinds of rare processes. In this paper we shortly remind the main recent results on Dark Matter, double beta decay, charge non-conserving processes, nucleon, di-nucleon and tri-nucleon decay.

We discuss the possibility that some of the microlensing events found by the MACHO collaboration towards the LMC might be due to lenses located in the LMC halo, rather then in the halo of the Milky Way. Indeed, the dark matter fraction in form of MACHOs of both Milky Way and LMC halos need not to be the same. For a MACHO mass in the range 0.1-0.3 M_⊙, the LMC halo fraction can be larger than the Milky Way one.

We present the results of the EROS-2 search for microlensing of stars in the Magellanic Clouds. Such events could be caused by macho dark matter in the Milky Way halo. Unlike all previous studies of Magellanic microlensing, we use only a subsample of 7 × 10⁶ bright stars. This strategy minimizes backgrounds due to variable stars and ensures accurate determination of lensing parameters by minimizing source confusion (blending). Using this sample of bright stars, only one candidate event was found, whereas ~ 42 events would have been expected if the Halo were entirely populated by objects of mass M ~ 0.4M_⊙. Combined with the results of EROS-1, this implies that the optical depth toward the Large Magellanic Cloud (LMC) due to such lenses is τ < 0.36 × 10^-7 (95%CL), corresponding to a fraction of the halo mass of less than 7%. This limit on the optical depth is at variance with the measurement of the MACHO collaboration near the center of the LMC, implying that a significant fraction of their events are due to lenses in the LMC itself.

GENIUS-TF-II is a setup of six naked high purity Ge detectors (15 kg) in liquid nitrogen in Gran Sasso. It has been installed in October, 2004 - after the first four naked Ge detectors had been installed on May 5, 2003 (GENIUS-TF-I). The GENIUS-Test-Facility (GENIUS-TF) is the first and up to now only setup ever testing the novel technique aiming at extreme background reduction in search for rare decays in particular underground. The goal of GENIUS-TF was to test some key operational parameters of the full GENIUS project proposal in 1997.^1,2,3,4,5,6 Simultaneous physical goal is to search for the annual modulation of the Dark Matter signal.^10,23

After operation of GENIUS-TF over three years with finally six naked Ge detectors (15 kg) in liquid nitrogen in Gran Sasso we realize the following problems: 1. Background from ²²²Rn diffusing into the setup, on a level far beyond the expectation. 2. Limited long-term stability of naked detectors in liquid nitrogen as result of increasing leakage current. None of the six detectors is running after three years with the nominal leakage current. Three of the six detectors do not work any more at all. These findings require further investigation on the way to a full-size GENIUS-like project.

In many Dark Matter (DM) frameworks, the annihilation of DM particles can produce gamma rays that extend up to very high energies. Since the 17m 'Major Atmospheric Gamma-ray Imaging Cherenkov (MAGIC) Telescope' has the lowest energy threshold of all existing Cherenkov telescopes, it is best suited to search for these signals. For the ongoing cycle-II observation period, part of the observation time has been allocated to indirect DM searches.

This review will include a short introduction to MAGIC and the characteristics of the observations, as well as the strategy for indirect DM searches using ground based Cherenkov telescopes.

A 107 kg NaI(Tl) experiment is projected at the Canfranc Underground Laboratory to look for dark matter particles by the annual modulation in their interaction rate. It will consist of 10 crystals selected from a set of 14 that remain underground since 1986. A first stage aiming at background and threshold reduction was performed with a 10.7 kg NaI(Tl) prototype, resulting in a new encapsulation design for the crystals. Low energy gamma sources were used for energy calibration and threshold determination. Background near threshold and natural chains internal contamination of some of the available crystals were studied. Results of the prototype and prospects of the future experiment are presented.

The XMASS experiment aims to detect pp and ⁷Be solar neutrinos, and neutrinoless double beta decay using ultra pure liquid xenon. It requires low background and a low threshold which will also enable us to search for dark matter in the galactic halo.

The first stage of XMASS project is concentrated on dark matter searches utilizes 800 kg liquid xenon detector. The detector design and expected sensitivity for dark matter based on Monte Carlo simulations will be presented.

Detection of negative daemons (Dark Electric Matter Objects – presumably the multiply electrically charged Planckian objects) in low–background conditions in September 2005 and March 2006 has provided supportive evidence for the expected to occur at that times maxima in the flux of daemons with V ≈ 10–15 km/s. These objects hit the Earth from the near–Earth, almost circular heliocentric orbits (NEACHOs). The ability of some FEU-167-1 PM tubes with a thicker inner Al coating to detect directly (without a scintillator) daemon passage through them has also been employed, an effect increasing ~ 100-fold the detector efficiency. As a result, the daemon flux recorded at the maxima was increased from ~10^-9 to 10^-7 cm^-2s^-1. At the maxima, two phases in the observed flux can be discriminated. The first of them is associated with objects moving in outer NEACHOs, which catch up with the Earth and cross it. The intensity and direction of the flux during this phase which lasts about two weeks depend on the time of day and latitude of observations (therefore, synchronous measurements in the northern and southern Earth's hemispheres are desirable). In the second phase, where the flux consists primarily of few objects transferred into geocentric, Earth-surface-crossing orbits during the first phase, the daytime and latitude dependence becomes less pronounced. All the experimental results thus obtained either support the conclusions following from the daemon paradigm or find a simple interpretation within it.

Dark matter experiments face two main challenges: low rate and low energy detection. Background reduction techniques are widely in development in order to improve sensitivity. Energy threshold is more technique-dependent and so it requires specific efforts for each detection approach. In this work we present some improvements in this line that open the possibility of further reduction in the energy threshold of scintillation experiments. Some preliminary results within the projected NaI(Tl) experiment ANAIS are reported.

We present preliminary results of measurements of the quenching factor for Na recoils in NaI(Tl) at room temperature, made at a dedicated neutron facility at the University of Sheffield. Measurements have been performed with a 2.45 MeV mono-energetic neutron generator in the energy range from 10 keV to 100 keV nuclear recoil energy. A BC501A liquid scintillator detector was used to tag neutrons. Cuts on pulse-shape discrimination from the BC501A liquid scintillator detector and neutron time-of-flight were performed on pulses recorded by a digitizer with a 2 ns sampling time. Measured quenching factors range from 19% to 26%, in agreement with other experiments. From pulse-shape analysis, a mean time of pulses from electron and nuclear recoils are compared down to 2 keV electron equivalent energy.

In this paper we show the possibility of constraining Dark Matter properties through multiwavelenght observations of the Sgr A* region. We consider Kaluza-Klein Dark Matter annihilation and study the resulting X-ray synchrotron and gamma-ray emission. We show how the combination of these observations puts severe constraints on the shape of a Kaluza-Klein Dark Matter halo.

AMS is a general purpose particle spectrometer constructed to measure cosmic rays and gamma rays on the International Space Station for a long duration flight. Selected performance simulations are reported for the search of dark matter signatures through the identification of positrons, antiprotons and gamma rays from WIMP annihilation in the Galaxy.

The detection of gamma-rays, antiprotons and positrons due to pair annihilation of dark matter particles in the Milky Way halo is a viable tecniques to search for supersymmetric dark matter candidates if there is the possibility to separate the signal from the backgroung generated by standard production mechanisms. Here we discuss the status of this indirect search and the prospective for the experiments GLAST and PAMELA.

ZEPLIN-III is a direct dark-matter search instrument using liquid xenon as a target. Both scintillation light and ionisation charge are measured. The instrument has been built and tested in a surface laboratory, and we present some of the results here, including design thermal control system verification, photomultiplier calibration and two-phase operation showing simultaneous measurement of scintillation and charge and position reconstruction.

The WIMPs search project PICO-LON has been started with multilayer thin NaI(Tl) crystals. The thin (0.05cm) and wide area (5cm × 5cm) NaI(Tl) crystals was successfully developed. The performances of thin NaI(Tl) scintillator was measured and they showed good energy resolution (20% at 60keV) and good position resolution (20% in 5cm × 5cm wider area).

The particle discrimination capability of various scintillating bolometers has been tested in the framework of the ROSEBUD (Rare Objects SEarch with Bolometers UnDerground) Dark Matter Search Collaboration. These detectors are well suited for dark matter searches. In particular, undoped sapphire has shown high light yield at very low temperature and low particle discrimination energy threshold. We will report on an estimate of the quenching factor in the heat signal for a scintillating bolometer made of this material, and we will present as well the prospects of the ROSEBUD experiment.

NEWAGE(NEw generation WIMP search with an Advanced Gaseous tracking device Experiment) project is a direction-sensitive dark matter search experiment with a gaseous micro time-projection-chamber(μ-TPC). We report on the performance of the μ-TPC with a detection volume of 23 × 28 × 30 cm³ operated with a carbon-tetrafiuoride (CF₄) of 0.2 bar.

The DRIFT dark matter experiment is located in the Boulby mine located on the east coast of northern England. It is a directionally sensitive detector capable of reconstructing nuclear recoils in three dimensions. Motivation and status of the experiment are discussed.

In the framework of the ArDM project, a next-generation one ton liquid argon WIMP detector, we built a 5 litre prototype chamber. This setup is primarily used to develop the appropriate read out for argon VUV scintillation light (128 nm) using wave length shifting dyes. The final aim is a energy threshold of 30 keV corresponding to yield of roughly 2% for detected photo-electrons. Beside light yield studies we investigate purity effects as well as background suppression power from the light pulse shape.

We study the dependence of the number of events required to directly detect a WIMP directional recoil signal on the capabilities of a directional detector. We consider variations in the nuclear recoil energy threshold, the background rate, whether the detector measures the recoil momentum vector in 2 or 3 dimensions and whether or not the sense of the momentum vector can be determined. The property with the biggest effect on the required exposure is the measurement of the momentum vector sense. If the detector cannot determine the recoil sense, the exposure required is increased by an order of magnitude for 3-d read–out and two orders of magnitude for 2-d read-out. For 2-d read-out the required exposure, in particular if the senses can not be measured, can be significantly reduced by analyzing the reduced angles with the, time dependent, projected direction of solar motion subtracted. The background rate effectively places a lower limit on the WIMP cross-section to which the detector is sensitive; it will be very difficult to detect WIMPs with a signal rate more than an order of magnitude below the background rate. Lowering the energy threshold also reduces the required exposure, but only for thresholds above 20 keV.

Zeplin-II is a two-phase (liquid, gas) Xenon detector optimised for WIMP Dark Matter search. Both scintillation and ionisation is measured, in order to discriminate the radioactive background. It is currently running in the underground laboratory of Boulby Mine (UK). 1 ton x day exposure has been collected. The preliminary study of 10% of the data is presented.

Scintillation in liquid Ar and Xe, and NaI(Tl) and CsI(Tl) crystals is discussed in relation with dark matter detectors. The nuclear quenching factors for liquid Xe and CsI(Tl) are almost the same. However, measured recoil ion to γ ratios, RN/γ, show the opposite trend in energy dependence. The electronic quenching, q_el, is responsible for the difference. The electronic LET is obtained and used to estimate q_el and RN/γ in CsI(Tl). The results show good agreement with neutron scattering experiments.

The complete 1-loop computation of the processes has been performed at an arbitrary c.m. energy for any pair of MSSM neutralinos. As an application suitable for Dark Matter (DM) searches, the neutralino-neutralino annihilation is studied at the limiting case v_ij → 0 describing the present DM distribution in the galactic halo, and at v_ij ≃ 0.5, determining the neutralino relic density contributions. Our results led to the FORTRAN code PLATONd-mgZ, which may be used for any set of real MSSM parameters. A sample of 6 MSSM models taken, already used in literature and effectively describing the various possible neutralino properties. A comparison with other existing works has also been made.

The current status of axion physics is presented. There still exists the axion window 10⁹ GeV ≤ F_a ≤ 10¹² GeV. The recent CAST solar axion search experiment on the axion-photon-photon coupling strength has to be improved by a factor of 100 to reach down to the region of superstring axions. The calculable and m_u = 0 cases for strong CP solutions, and axino cosmology in SUSY extension of axion are also commented.

The working principle of axion helioscopes can be behind unexpected solar X-ray emission. Because this is associated with solar magnetic fields (~B²), which become in this framework the catalyst and not the otherwise suspected/unspecified energy source of solar X-rays. In addition, the built–in fine tuning we may (not) be able to fully reconstruct, and, we may (not?) be able to copy. Solar axion signals are transient brightenings, or, continuous radiation violating the second law of thermodynamics and Planck's law of black body radiation. To understand the corona problem and other mysteries like flares, sunspots, etc., we arrive at two exotica: a) trapped, radiatively decaying, massive axions allow a continuous self-irradiation of the Sun, explaining the sudden temperature inversion ~2000 km above the surface and b) outstreaming light axions interact with local fields (~B²), depending crucially on the plasma frequency which must match the axion rest mass, explaining the otherwise unpredictable transient solar phenomena. Then, the energy of a related phenomenon points at the birth place of involved axions. For example, this suggests that the ~2 MK solar corona has its axion roots at the top of the radiative zone. The predicted B ≈ 10–50 T make this place a coherent axion source, while the multiple photon scattering enhances the photon-to-axion conversion unilaterally, since axions escape. We conclude that the energy range below some 100 eV is a window of opportunity for axion searches, and that it coincides with a) the derived photon energies for an external self-irradiation of the Sun, which has to penetrate until the transition region, and b) with the bulk of the soft solar X-ray luminosity of unknown origin. Thus, indirect signatures support axions or the like as an explanation of enigmatic behaviour in the Sun and beyond. Axion antennas could take advantage of such a feed back.

Micropattern detectors (MPD) and in particular MICROMEGAS are being developed very actively in recent years. While increasingly used now in high energy physics experiments, their application to rare event searches is relatively more recent. In this talk the status of three initiatives in this respect are presented: MICROMEGAS for axion searches in the CAST experiment at CERN, the use of MICROMEGAS technology to measure the recoil direction in WIMP searches, and the development of the spherical TPC concept with applications in low energy neutrino detection.

Precision experiments exploiting low-energy photons may yield information on particle physics complementary to experiments at high-energy colliders, in particular on new very light and very weakly interacting particles, predicted in many extensions of the standard model. Such particles may be produced by laser photons send along a transverse magnetic field. The laser polarization experiment PVLAS may have seen the first indirect signal of such particles by observing an anomalously large rotation of the polarization plane of photons after the passage through a magnetic field. This can be interpreted as evidence for photon disappearance due to particle production. There are a number of experimental proposals to test independently the particle interpretation of PVLAS. Many of them are based on the search for photon reappearance or regeneration, i.e. for "light shining through a wall". At DESY, the Axion-Like Particle Search (ALPS) collaboration is currently setting up such an experiment.

We show that the Ω_b - Ω_DM coincidence can naturally be explained in a framework where axino cold dark matter is predominantly produced in non-thermal processes involving decays of Q-balls formed in Affleck-Dine baryogenesis. In this approach the similarity between Ω_b and Ω_DM is a direct consequence of the (sub-)GeV scale of the mass of the axino.

An extension of the Standard Model by three right-handed neutrinos with masses smaller than the electroweak scale (the νMSM) can explain simultaneously dark matter and baryon asymmetry of the Universe, being consistent with the data on neutrino oscillations. A dark matter candidate in this theory is the sterile neutrino with the mass in keV range. We discuss the constraints on the properties of this particle and mechanisms of their cosmological production. Baryon asymmetry generation in this model is reviewed. Crucial experiments that can confirm or rule out the νMSM are briefly discussed.

Neutrino-less double beta decays are of great interest for studying the Majorana nature of ν's, the ν mass spectrum, the absolute ν-mass scale, the Majorana CP phases and other properties of neutrinos and weak interactions. The present ββ detectors with sensitivities of 150 ~ 300 meV are used to study the quasi-degenerate ν masses. Future higher-sensitivity experiments with mass sensitivities of the atmospheric and solar ν-masses are indispensable for studying ν-masses in the inverted and normal hierarchy spectra, respectively. Theoretical and experimental studies for evaluating nuclear matrix elements M^0ν are cruial for extracting the ν mass. This report is a brief review of double beta decays and neutrinos with emphasis on future 0νββ experiments for the Majorana ν mass in the 30-100 meV region.

This paper describes the lessons we have to draw after the observation of neutrino-less ββ decay by the enriched ⁷⁶Ge experiment, for present and future experiments (a) to fulfill the task to confirm the present result (b) to deliver additional information on the main contributions, of effective neutrino mass and right-handed weak currents etc. to the 0νββ amplitude. It is pointed out that presently running and planned experiments are mostly not sensitive enough to check the present evidence on a reasonable time scale. More important, the only way to get more information on the individual contributions of m, η, λ etc. to the 0νββ amplitude is to go to completely different types of experiments, e.g. mixed-mode β⁺EC decay experiments, such as ¹²⁴Xe decay.

Neutrinoless double beta (0νββ)-decay could be the key to understanding the nature of the neutrino. The GErmanium Detector Array (GERDA) is designed to search for 0νββ-decay of the isotope ⁷⁶Ge. Germanium crystals enriched in ⁷⁶Ge, acting as source and detector simultaneously, will be submerged directly into their ultra pure cooling medium that also serves as a radiation shield. This concept will allow for a reduction of the background by up to two orders of magnitudes with respect to earlier experiments.

In this letter in the framework of a simple see-saw scenario with three quasi degenerate Majorana neutrinos we propose that one of these neutrinos can be very weakly coupled, yet there is a mechanism of the generation of the abundance of such "dark" neutrino in the early universe. The mechanism of production is due to oscillations between "dark" Majorana neutrino and one of the Majorana's which has relatively large Yukawa couplings ("bright" Majorana neutrino). The transition of "bright" Majorana into a "dark" one is nonadiabatic. We point out on the similarity with the Landau-Zener transition regime. In our model one can explain the observed dark matter density, present matter-antimatter asymmetry and active neutrino data all at the same time.

IceCube is a kilometer scale high-energy neutrino observatory, currently under construction at the South Pole. It is a photo-detector, using the deep Antarctic ice as detection medium for the Cherenkov photons induced by relativistic charged particles. These charged particles may be atmospheric muons or reaction products from neutrino interactions in the vicinity of the instrumented volume. The experiment searches for neutrinos originating in astrophysical sources, and can also detect neutrinos from WIMP interaction in the Sun or Earth. In the last two austral summers, 9 in-ice strings and 16 surface IceTop stations (out of up to 80 planned) were successfully deployed, and the detector has been taking data ever since. In this proceedings, IceCube design, present status, performance and dark matter detection sensitivities will be discussed.

The ANTARES Collaboration is building an underwater neutrino telescope in the Mediterranean Sea, at a depth of 2500 m, 40 km offshore from Toulon (France). The main goal of the detector is the search for high energy neutrinos from possible Galactic and extra-Galactic sources as well as from the decay of neutralinos and other exotic particles. The present status of the detector, with the first two lines in acquisition since Mar and Sep 2006, is presented.

The "HEllenic LYceum Cosmic Observatories Network" - HELYCON collaboration is constructing a network of detector stations distributed over three extended geographical areas. The goal of HELYCON is to observe Extensive Air Showers and to collect data corresponding to the flux, the direction and possible correlations between very energetic cosmic rays. In this report the design, the construction and the performance of a prototype detector array is presented. The results of a feasibility study on the use of HELYCON detectors for the calibration of the Mediterranean neutrino telescope, KM3NeT, are also presented.

Universal extra dimension (UED) models with right-handed neutrinos are studied. The introduction of the neutrinos makes us possible not only to describe Dirac neutrino masses but also to solve the cosmological problem called the KK graviton problem. This problem is essentially caused by the late time decay of a KK photon into a KK graviton and a photon, and it distorts the spectrum of the cosmic microwave background or the diffuse photon. We point out that, once we introduce right-handed neutrinos to UED models, the KK photon decays dominantly into neutrinos and does not emit a photon. We also discuss sub-dominant modes with a photon in the decay quantitatively, and show that their branching ratios are so small that the spectra are not distorted.

Neutron background for the high-sensitivity dark matter experiments is discussed. Neutron production via spontaneous fission and (α, n) reactions from U and Th, and by cosmic-ray muons is considered.

The ArDM project aims at operating a large noble liquid detector to search for direct evidence of Weakly Interacting Massive Particles (WIMP) as Dark Matter in the universe. Background sources relevant to ton-scale liquid and gaseous argon detectors, such as neutrons from detector components, muon-induced neutrons and neutrons caused by radioactivity of rock, as well as the internal ³⁹Ar background, are studied with simulations. These background radiations are addressed with the design of an appropriate shielding as well as with different background rejection potentialities. Among them the project relies on event topology recognition, event localization, density ionization discrimination and pulse shape discrimination. Background rates, energy spectra, characteristics of the background-induced nuclear recoils in liquid argon, as well as the shielding performance and rejection performance of the detector are described.

The new Laboratorio Subterráneo de Canfranc (LSC) was inaugurated on March 2006. We report the first measurements of radon concentration, gamma background and muon fluxes performed in the Laboratory.

A technique to measure low intensity fast neutron flux has been developed in order to measure the neutron background from rock at the Boulby Underground Laboratory (2800 m.w.e.). The experiment was performed using a liquid scintillation detector loaded with Gd. A flux of fast neutrons from rock was measured as (1.72 ± 0.61(stat.) ± 0.38(syst.)) × 10^-6 cm^-2 s^-1 above 0.5 MeV.

The propagation of radiation in several possible shielding designs for future large-scale dark matter search experiments has been simulated with respect to the muon-induced background using the GEANT4 Monte Carlo toolkit. Results indicate that it seems to be advisable to have as few high-Z materials as possible in the vicinity of the detector.

Since neutrons provide the principal background in direct dark matter detection experiments, the simulation of neutron induced nuclear recoils is crucial for background reduction. GEANT4 provides a framework for such simulations. While the simulation of the elastic scattering reactions agrees very well with the theoretical expectations, the simulation of the inelastic scatterings generally fails, i.e. energy conservation per reaction and angular–energy correlation of the recoiling nucleus are not respected. An improved code is used to correct these shortcomings. Further necessary improvements are addressed as well.

The sensitivity of future large-scale dark matter detectors may be limited by neutrons produced in detector components. For this reason it is important to use pure materials and estimate the background from this source. Neutrons are produced via spontaneous fission and (α, n) reactions from U and Th traces in the materials. To estimate neutron yields and spectra, the cross-sections of (α, n) reactions and probabilities of transitions to different excited states should be known. In this work these cross-sections and probabilities are calculated using EMPIRE-2.19 for some isotopes and compared to the experimental data. The results have been used to calculate neutron spectra from materials with the code SOURCES4. We plan to create a database of the (α, n) cross sections and neutron spectra for materials used in dark matter detectors. This work is on-going as part of the EU FP6 programme ILIAS.

The XENON10 Experiment is a dual (liquid/gas) phase time-projection chamber designed for direct detection of dark matter via elastic scattering of the Xe nuclei. It was deployed in March 2006 at LNGS (~ 3100 mwe) and is presently operational. The ratio of prompt (primary) scintillation to secondary scintillation (via electro-luminesence caused by ionization electrons extracted into the gas phase) allows event-by-event discrimination of electron and nuclear recoil events. A threshold < 10 keV nuclear recoil energy (keVr) is demonstrated, as well as a background rate of < 1 cts/kg/keVee/day (dru) before rejection. With 3-D position reconstruction (to define a fiducial region) and > 99% discrimination of gamma background (at 50% acceptance for nuclear recoils), XENON10 expects to be sensitive to a WIMP-nucleon interaction cross section of < 10^-43 cm² for WIMP particles with mass > 50 GeV.

Several techniques must be combined to reduce the background level close to the value needed in the new generation experiments to search for the neutrinoless double beta decay of the ⁷⁶Ge, we have to combine several techniques. Three of the most important points to study are: granularity, segmentation of the crystals and spatial resolution of the detector directly correlated with an offline Pulse Shape Analysis (PSA). Preliminary studies about these strategies for background reduction were developed during last months, obtaining some promising results.

A backside illuminated pn-CCD detector in conjunction with an X-ray mirror optics is one of the three detectors used in the CERN Axion Solar Telescope (CAST) to register the expected photon signal. A background study performed for this detector shows that the level (8.00 ± 0.07) × 10^-5 counts cm^-2 s^-1 keV^-1 between 1 and 7 keV is to be dominated by the external gamma background due to natural activities at the experimental site, while radioactive impurities in the detector itself and cosmic neutrons contribute a much smaller fraction.

The ZEPLIN-II detector has completed two months production run. The data acquisition system is described. Parameterisation of events and data reduction are discussed.

DRIFT-II is a dark matter detector designed to measure WIMP recoils in three dimensions. It uses this information for background discrimination as well as a means to seek an isotropy as a positive signal for dark matter detection. Methods for three dimensional track reconstruction of DRIFT-II event data are presented.

The keV energy sensitivity of superfluid ³He bolometers is due to the extremely small heat capacity of this fluid. At ultra-low temperatures, however, their thermal response may be dominated by a few atomic layers of adsorbed ³He. We report on direct measurements of this effect, as well as on the techniques that allow to suppress it to achieve the highest detection sensitivity.

The ZEPLIN II experiment utilizes an active neutron veto below and to the sides of the 35 kg liquid xenon target. We describe the veto hardware and present some preliminary results of performance measurements.

The missing mass problem is the longest standing problem of modern cosmology. This is readily solved by positing the existence of an unknown form of matter, called the dark matter. Still, a particle with the properties required is yet to be found experimentally. An alternative explanation is that gravity deviates from General Relativity for small enough accelerations. One such a theory was proposed by Bekenstein, building on earlier work of Sanders and Milgrom. The theory has a tensor, a vector and a scalar field as dynamical agents of gravity and is thus called Tensor–Vector–Scalar (TeVeS). In this talk I give a short overview of TeVeS theory and discuss its cosmology.

We review the high-redshift X-ray selected AGN clustering, based on the XMM/2dF survey, and compare it with other recent XMM-based results. Using the recent Hasinger et al. (2005) and La Franca et al. (2005) luminosity functions we find that the spatial clustering lengths, derived using Limber's inversion equation, are ~ 17 and 20 h^-1 Mpc for the soft and hard band sources while their median redshifts are and 0.8, respectively. The corresponding bias factors at are ~ 5.3 ± 0.9 and ~ 5.1 ± 1.1, respectively. Within the framework of a flat cosmological model we find that our results support a model with Ω_m ≃ 0.26, σ₈ ≃ 0.75, h ≃ 0.72, w ≃ -0.9 (in excellent agreement with the 3 year WMAP results). We also find the present day bias of X-ray AGNs to be b_o ~ 2.

I review some results on the galaxy/light-mass connection obtained by dissipationless simulations in combination with a simple, non-parametric model to connect halo circular velocity to the luminosity of the galaxy they would host. Ia focus on the galaxy-mass correlation and mass-to-light ratios obtained from galaxy up to cluster scales. The predictions of this simple scheme are shown to be in very good agreement with SDSS observations.

The relic density of a cold dark matter (CDM) candidate is calculated in the context of three non-standard cosmological scenaria and its value is compared with the one obtained in the standard regime. In particular, we consider the decoupling of the CDM particle during: (i) A decaying-particle dominated phase or (ii) a kinetic-energy dominated phase or (iii) the decay of a massive particle under the complete or partial domination of kination. We use plausible values (from the viewpoint of supersymmetric models) for the mass and the thermal averaged cross section times the velocity of the cold relic and we investigate scenaria of equilibrium and non-equilibrium production. In the case (i) a low reheat temperature, in the range (1 – 20) GeV, significantly facilitates the achievement of an acceptable CDM abundance. On the other hand, the presence of kination in the case (ii) can lead to an enhancement of the CDM abundance up to three orders of magnitude. The latter enhancement can be avoided, in the case (iii). In a such situation, the temperature turns out to be frozen to a plateau value which is, mostly, lower than about 40 GeV.

The energy density of the universe seems to be dominated by a mysterious "dark-energy" which drives the acceleration of the expansion. This phenomenon was discovered by mapping out the history of cosmic expansion using Type Ia supernovae (SNe Ia) as distance indicators. SNe Ia currently provide one of the best way to characterize the nature of dark energy, by placing tight limits on its equation of state w = p/ρ. Current high-redshift supernova surveys, such as the 5-year Supernova Legacy Survey will deliver ~ 1000 SN Ia detections with well-sampled griz light curves. Using this unprecedented dataset, a statistical precision of about 5% will be obtained on Ω_Λ and w. In this contribution, I review the ongoing Type Ia surveys and present the recent constraints obtained on the dark energy equation of state.

In this talk we review briefly the basic features of non-critical (dissipative) String Cosmologies, and we confront some of these models with supernova data. We pay particular attention to the off-shell and dilaton contributions to the dynamical evolution equations of the non-critical string Universe, as well as the Boltzmann equation for species abundances. The latter could have important consequences for the modification of astrophysical constraints on physically appealing particle physics models, such as supersymmetry. The data fits show that non-critical string cosmologies may be viable alternatives to ΛCDM model.

Quintessential inflation is studied using a string modulus as the inflaton–quintessence field. It is assumed that the modulus crosses an enhanced symmetry point (ESP) in field space. Particle production at the ESP temporarily traps the modulus resulting in a period of inflation. After reheating, the modulus freezes due to cosmological friction at a large value, such that its scalar potential is dominated by contributions due to fluxes in the extra dimensions. The modulus remains frozen until the present, when it can become quintessence.

The observed current accelerating expansion of the universe can be attributed to either the existence of a negative pressure energy component (dark energy) in the universe or to modifications of general relativity. The discovery of observational signatures that may distinguish between the two classes of theories is a major challenge for modern cosmology. Here I briefly discuss one such potential signature: The change of sign of the expression (where H(z is the Hubble parameter at redshift z) which is equivalent to an equation of state parameter w(z) crossing the w = - 1 line. I also review the current information provided by observational probes with respect to the above cosmological test.

In this contribution we apply model selection approach based on Akaike criterion as an estimator of Kullback-Leibler entropy. In particular, we present the proper way of ranking the competing models based on Akaike weights (in Bayesian language - posterior probabilities of the models). This important ingredient is missing in alternative studies dealing with cosmological applications of Akaike criterion.

Out of many particular models of dark energy we focus on four: quintessence, quintessence with time varying equation of state, brane-world and generalized Chaplygin gas model and test them on Riess' Gold sample.

As a result we obtain that the best model - in terms of Akaike Criterion - is the quintessence model with evolving equation of state. The odds suggest that although there exist differences in the support given to specific scenarios by supernova data all models considered receive similar support. One can also notice that models similar in structure i.e. ΛCDM, quintessence and quintessence with variable equation of state are closer to each other in terms of Kullback-Leibler entropy. Models having different structure i.e. Chaplygin gas or brane-world scenario are more distant (in Kullback-Leibler sense) from the best one.

We study static configurations of dark matter coupled to a scalar field responsible for the dark energy of the Universe. The dark matter is modelled as a Fermi gas within the Thomas-Fermi approximation. The mass of the dark matter particles is a function of the scalar field. We analyze the profile of the dark matter halos in galaxies. In this case our framework is equivalent to the model of the isothermal sphere. In the presence of a scalar field, the velocity of a massive object orbiting the galaxy is not of the order of the typical velocity of the dark matter particles, as in the conventional picture. Instead, it is reduced by a factor that quantifies the dependence of the dark matter mass on the scalar field. This has implications for dark matter searches.

EURECA (European Underground Rare Event Calorimeter Array) is a new project, searching for dark matter. The collaboration is comprised largely of the present groups of the CRESST and EDELWEISS experiments and several new groups. The aim is to explore scalar cross sections in the 10^-9 - 10^-10 picobarn region with a target mass of up to one tonne. A major advantage of EURECA is the planned use of more that just one target material (multi target experiment for WIMP identification). In preparation for this large-scale experiment, R&D for EURECA is provided through the current phases of CRESST and EDELWEISS.

LIST OF PARTICIPANTS.