The CRESST dark matter search

The aim of CRESST (Cryogenic Rare Event Search with Superconducting Thermometers) is to search for particle dark matter via elastic scattering off nuclei. The experiment is located at the Laboratori Nazionali del Gran Sasso (LNGS), Italy, and it uses low-background cryogenic detectors with superconducting phase-transition thermometers for the direct detection of WIMP-nucleus scattering events.     

Direct detection searches for WIMP dark matter

A very active hunt is underway to discover the composition of dark matter in the universe. A large effort is devoted to the direct detection of dark matter through interactions with detectors in the laboratory. In this paper, we give an overview of the dark matter problem, discuss some of the design considerations taken in direct detection experiments, and describe some of the current efforts to discover Weakly Interacting Massive Particles (WIMPs), a well-motivated class of candidates for dark matter.     

Secondary scintillation yield from GEM and THGEM gaseous electron multipliers for direct dark matter search

The search for alternatives to PMTs as photosensors in optical TPCs for rare event detection has significantly increased in the last few years. In particular, in view of the next generation large volume detectors, the use of photosensors with lower natural radioactivity, such as large area APDs or GM-APDs, with the additional possibility of sparse surface coverage, triggered the intense study of secondary scintillation production in micropattern electron multipliers, such as GEMs and THGEMs, as alternatives to the commonly used uniform electric field region between two parallel meshes. The much higher scintillation output obtained from the electron avalanches in such microstructures presents an advantage in those situations. The accurate knowledge of the amount of such scintillation is important for correct detector simulation and optimization. It will also serve as a benchmark for software tools developed and/or under development for the calculation of the amount of such scintillation.     

Neutrino mass models and dark matter

We discuss a possibility to relate neutrino mass to dark matter. If we suppose that neutrino masses are generated through a radiative seesaw mechanism, dark matter may be identified with a stable field which is relevant to the neutrino mass generation. The model is severely constrained by lepton flavor violating processes. We show some solutions to this constraint.     

PAMELA,FGST and sub-TeV dark matter

PAMELA's observation that the cosmic ray positron fraction increases rapidly with energy implies the presence of primary sources of energetic electron–positron pairs. Of particular interest is the possibility that dark matter annihilations in the halo of the Milky Way provide this anomalous flux of antimatter. The recent measurement of the cosmic ray electron spectrum by the Fermi Gamma Ray Space Telescope, however, can be used to constrain the nature of any such dark matter particle. In particular, it has been argued that in order to accommodate the observations of Fermi and provide the PAMELA positron excess, annihilating dark matter particles must be as massive as ∼1 TeV or heavier. In this Letter, we revisit Fermi's electron spectrum measurement within the context of annihilating dark matter, focusing on masses in the range of 100–1000 GeV, and considering effects such as variations in the astrophysical backgrounds from the presence of local cosmic ray accelerators, and the finite energy resolution of the Fermi Gamma Ray Space Telescope. When these factors are taken into account, we find that dark matter particles as light as ∼300 GeV can be capable of generating the positron fraction observed by PAMELA.     

The spacetime associated with galactic dark matter halos

We show how an adequate post-Newtonian generalization can be obtained for Newtonian dark matter halos associated with an empiric density profile. Applying this approach to halos that follow from the well known numerical simulations of Navarro, Frenk and White (NFW), we derive all dynamical variables and show that NFW halos approximately follow an ideal gas type of equation of state which fits very well to a polytropic relation in the region outside the core. This fact suggests that outer regions of NFW halos might be related to equilibrium states in the non-extensive Statistical Mechanics formalism proposed by Tsallis.     

Ice shielding in the large scale GENIUS experiment for double beta decay and dark matter search

We suggest here the use of ice as shielding material in the large scale GENIUS experiment for the ultimate sensitive double beta decay and dark matter search. The idea is to pack a working volume of several tons of liquid nitrogens, which contains the “naked” Ge detectors, inside an ice shielding. Very thin plastic foil would be used in order to prevent leakage of the liquid nitrogen. Due to the excellent advantages of ice shielding (high purity and low cost, self-supporting ability, thermo-isolation and optical properties, safety) this could be another possible way of realization of the GENIUS project. Received: 30 July 1998     

Minimal Dirac fermionic dark matter with nonzero magnetic dipole moment

A neutral Dirac fermion ψ   with a nonzero magnetic dipole moment is supplied as a singlet within the context of the standard model and is considered as a dark matter candidate near the electroweak scale (10–1000 GeV$10\text{–}1000\text{GeV}$). We discuss its dynamics with the ordinary matters through the magnetic dipole moment. The magnetic dipole moment constrained by the relic abundance may be as large as ¹⁰⁻¹⁸–¹⁰⁻¹⁷e⋅cm${10}^{-18}\text{–}{10}^{-17}e\cdot \text{cm}$. We show that the elastic scattering is due to a spin–spin interaction for the direct detections and the predictions are under experimental exclusion limits of the current direct detectors, XENON10 and CDMS II, and consider the possibility of dark matter detection in the future.     

A conformal gauge mediation and dark matter with only one mass parameter

If the supersymmetry (SUSY) is a solution to the hierarchy problem, it is puzzling that any SUSY particle has not been discovered yet. We show that there is a low-scale conformal gauge mediation model which contains all necessary ingredients, i.e. not only a SUSY-breaking dynamics and a gauge mediation mechanism, but also a candidate for the dark matter. The model has only one free mass parameter, that is, the mass for messengers. In this model, the dark matter is provided by a composite particle in the SUSY-breaking sector, and the observed value of the dark matter density uniquely fixes the mass of messengers at the order of 10² TeV. Then, the sfermion and gaugino masses are fixed to be of order ¹⁰²–¹⁰³ GeV${10}^2\text{–}{10}^3\text{GeV}$ without any arbitrariness, thus the SUSY particles are expected not to be discovered at the Tevatron or LEP, while having a discovery possibility at the LHC.     

Indirect detection of dark matter, current status and recent results

Since its launch in 2008, the Large Area Telescope, onboard the Fermi Gamma-ray Space Telescope, has detected the largest amount of gamma rays, in the 20 MeV 300 GeV energy range and electrons + positrons in the 7 GeV-1 TeV range. These impressive statistics allow one to perform a very sensitive indirect experimental search for dark matter. I will present the latest results on these searches.     

Naturalness,supersymmetry and implications for LHC and dark matter

It is shown that the Hyperbolic Branch of the radiative electroweak symmetry breaking contains in it three regions: the Focal Point, Focal Curves, and Focal Surfaces. Further, the Focal Point is shown to lie on the boundary of a Focal Curve. These focal regions allow for a small μ while scalar masses can become large and may lie in the several TeV region. It is shown that for the mSUGRA model the current LHC-7 constraint depletes the Focal Point region while regions on Focal Curves and Focal Surfaces remain largely intact. The LHC implications for models which lie on Focal Curves are briefly discussed as well as the implications of dark matter constraints for the Focal Point, Focal Curves and Focal Surfaces are discussed.     

Final results of the EDELWEISS-II WIMP search using a 4-kg array of cryogenic germanium detectors with interleaved electrodes

The EDELWEISS-II Collaboration has completed a direct search for WIMP dark matter with an array of ten 400-g cryogenic germanium detectors in operation at the Laboratoire Souterrain de Modane. The combined use of thermal phonon sensors and charge collection electrodes with an interleaved geometry enables the efficient rejection of γ-induced radioactivity as well as near-surface interactions. A total effective exposure of 384 kg d has been achieved, mostly coming from fourteen months of continuous operation. Five nuclear recoil candidates are observed above 20 keV, while the estimated background is 3.0 events. The result is interpreted in terms of limits on the cross-section of spin-independent interactions of WIMPs and nucleons. A cross-section of 4.4×¹⁰−8 pb is excluded at 90%CL for a WIMP mass of 85 GeV. New constraints are also set on models where the WIMP-nucleon scattering is inelastic.     

Constraining dark matter properties with gamma-rays from the Galactic Center with Fermi-LAT

We study the capabilities of the Fermi-LAT instrument on board of the Fermi mission to constrain particle dark matter properties, as annihilation cross section, mass and branching ratio into dominant annihilation channels, with gamma-ray observations from the Galactic Center. Besides the prompt gamma-ray flux, we also take into account the contribution from the electrons/positrons produced in dark matter annihilations to the gamma-ray signal via inverse Compton scattering off the interstellar photon background, which turns out to be crucial in the case of dark matter annihilations into μ⁺μ⁻ and e⁺e⁻ pairs. We study the signal dependence on different parameters like the region of observation, the density profile, the assumptions for the dark matter model and the uncertainties in the propagation model. We also show the effect of the inclusion of a 20% systematic uncertainty in the gamma-ray background. If Fermi-LAT is able to distinguish a possible dark matter signal from the large gamma-ray background, we show that for dark matter masses below ∼200 GeV, Fermi-LAT will likely be able to determine dark matter properties with good accuracy.     

First underground results with NEWAGE-0.3a direction-sensitive dark matter detector

A direction-sensitive dark matter search experiment at Kamioka underground laboratory with the NEWAGE-0.3a detector was performed. The NEWAGE-0.3a detector is a gaseous micro-time-projection chamber filled with CF₄ gas at 152 Torr. The fiducial volume and target mass are 20×25×31 cm³$20\times 25\times 31{\text{cm}}^3$ and 0.0115 kg, respectively. With an exposure of 0.524 kg days, improved spin-dependent weakly interacting massive particle (WIMP)-proton cross section limits by a direction-sensitive method were achieved including a new record of 5400 pb for 150 GeV/c²$/c^2$ WIMPs. We studied the remaining background and found that ambient γ-rays contributed about one-fifth of the remaining background and radioactive contaminants inside the gas chamber contributed the rest.     

Matter and dark matter from false vacuum decay

We study tachyonic preheating associated with the spontaneous breaking of B−L$B-L$, the difference of baryon and lepton number. Reheating occurs through the decays of heavy Majorana neutrinos which are produced during preheating and in decays of the Higgs particles of B−L$B-L$ breaking. Baryogenesis is an interplay of nonthermal and thermal leptogenesis, accompanied by thermally produced gravitino dark matter. The proposed mechanism simultaneously explains the generation of matter and dark matter, thereby relating the absolute neutrino mass scale to the gravitino mass.     

CaWO4晶体中F型色心电子结构的研究

运用相对论的密度泛函离散变分法(DV-Xα)研究了CaWO₄晶体中F型色心的电子结构. 计算结果表明，F和F⁺心在禁带中引入了新的施主能级；分析了晶体内可能存在的光学跃迁模式，并通过过渡态的方法计算了F，F⁺心跃迁到导带底的能量分别为1.92eV和2.42eV. 因此，从理论上推断了F和F⁺心在CaWO₄晶体中可能引起650nm和515nm的吸收，由此说明CaWO₄晶体中650nm和515nm吸收带起源于晶体中的F和F⁺心. 关键词： 4晶体')" href="#">CaWO₄晶体 +心')" href="#">F和F⁺心 DV-Xα     

Indirect dark matter searches in our Galaxy in comparison with FERMI data

The first 2-year data on the diffuse gamma rays from the FERMI satellite are analyzed and compared with expectations from dark matter annihilation. Although the published results at intermediate latitudes do not confirm the EGRET GeV excess, the data towards the Galactic center are hard to explain with standard propagation models. Redoing a template shape fit to the data in about 900 independent sky directions reveals that the FERMI data are best described by including a DMA contribution from an NFW DM profile with a ringlike DM substructure, as required to describe the new precise data on the gas flaring and rotation curve.     

Dark energy interacting with dark matter and a third fluid: Possible EoS for this component

A cosmological model of dark energy interacting with dark matter and another general component of the universe is considered. The equations for the coincidence parameters r and s, which represent the ratios between dark energy and dark matter and the other cosmic fluid respectively, are analyzed in terms of the stability of stationary solutions. The obtained general results allow to shed some light on the equations of state of the three interacting fluids, due to the constraints imposed by the stability of the solutions. We found that for an interaction proportional to the sum of the dark energy density and the third fluid density, the hypothetical fluid must have positive pressure, which leads naturally to a cosmological scenario with radiation, unparticle or even some form of warm dark matter as the third interacting fluid.     

Entropy, baryon asymmetry and dark matter from heavy neutrino decays

The origin of the hot phase of the early universe remains so far an unsolved puzzle. A viable option is entropy production through the decays of heavy Majorana neutrinos whose lifetimes determine the initial temperature. We show that baryogenesis and the production of dark matter are natural by-products of this mechanism. As is well known, the cosmological baryon asymmetry can be accounted for by leptogenesis for characteristic neutrino mass parameters. We find that thermal gravitino production then automatically yields the observed amount of dark matter, for the gravitino as the lightest superparticle and typical gluino masses. As an example, we consider the production of heavy Majorana neutrinos in the course of tachyonic preheating associated with spontaneous B−L breaking. A quantitative analysis leads to constraints on the superparticle masses in terms of neutrino masses: For a light neutrino mass of ¹⁰−5 eV the gravitino mass can be as small as 200 MeV, whereas a lower neutrino mass bound of 0.01 eV implies a lower bound of 9 GeV on the gravitino mass. The measurement of a light neutrino mass of 0.1 eV would rule out heavy neutrino decays as the origin of entropy, visible and dark matter.     

Model-independent approach for dark matter phenomenology: Signatures in linear colliders and cosmic positron experiments

We have studied the phenomenology of dark matter at the ILC and cosmic positron experiments based on model-independent approach. We have found a strong correlation between dark matter signatures at the ILC and those in the indirect detection experiments of dark matter. Once the dark matter is discovered in the positron experiments such as the PAMELA, its nature will be investigated in detail at the ILC.