Secluded WIMP dark matter

We consider a generic mechanism via which thermal relic WIMP dark matter may be decoupled from the Standard Model, namely through a combination of WIMP annihilation to metastable mediators with subsequent delayed decay to Standard Model states. We illustrate this with explicit examples of WIMPs connected to the Standard Model by metastable bosons or fermions. In all models, provided the WIMP mass is greater than that of the mediator, it can be secluded from the Standard Model with an extremely small elastic scattering cross-section on nuclei and rate for direct collider production. In contrast, indirect signatures from WIMP annihilation are consistent with a weak scale cross-section and provide potentially observable γ-ray signals. We also point out that γ-ray constraints and flavor physics impose severe restrictions on MeV-scale variants of secluded models, and identify limited classes that pass all the observational constraints.     

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.     

Direct detection of WIMP dark matter

The question of the nature of dark matter in the universe is perhaps the greatest problem facing cosmology and particle physics at present. New observations of the cosmic microwave background radiation and distant supernovae show that more that 90% of the mass in the universe is in the form of some unknown matter. Many lines of evidence from cosmology and particle physics suggest that the best candidate for this dark matter is a weakly interacting massive particle, or WIMP. Such particles are predicted by supersymmetry, a theory extending the Standard Model of particle physics, and many experiments around the world are now trying to directly detect these WIMPs. This article reviews the reasons for believing WIMPs to be the dark matter, and considers the challenges involved in detecting their rare low-energy interactions with normal matter. Current experimental searches are reviewed with regard to the claimed detection of WIMPs by the DAMA group. These experiments are just beginning to reach the sensitivity needed to detect, or rule out, supersymmetric WIMPs, and higher sensitivity future experiments are also discussed.     

Anisotropic scintillators for WIMP direct detection: revisited

The possibility to effectively exploit the directionality of the measured counting rate as a signature for WIMPs by using anisotropic scintillators is revisited and discussed in some details. Received: 21 October 2002 / Published online: 14 April 2003     

神奇的自然常量h

在物理学基本常量中，普朗克常量h是一个奇特而又神奇的常量，本对普朗克常量h在现代物理学中的特殊地位及其所发挥的重要作用做了分析、论述。     

WIMP dark matter from gravitino decays and leptogenesis

The spontaneous breaking of B−L$B-L$ symmetry naturally accounts for the small observed neutrino masses via the seesaw mechanism. We have recently shown that the cosmological realization of B−L$B-L$ breaking in a supersymmetric theory can successfully generate the initial conditions of the hot early universe, i.e. entropy, baryon asymmetry and dark matter, if the gravitino is the lightest superparticle (LSP). This implies relations between neutrino and superparticle masses. Here we extend our analysis to the case of very heavy gravitinos which are motivated by hints for the Higgs boson at the LHC. We find that the nonthermal production of ‘pure’ wino or higgsino LSPs, i.e. weakly interacting massive particles (WIMPs), in heavy gravitino decays can account for the observed amount of dark matter while simultaneously fulfilling the constraints imposed by primordial nucleosynthesis and leptogenesis within a range of LSP, gravitino and neutrino masses. For instance, a mass of the lightest neutrino of 0.05 eV$0.05\text{eV}$ would require a higgsino mass below 900 GeV$900\text{GeV}$ and a gravitino mass of at least 10 TeV$10\text{TeV}$.     

Constraining WIMP magnetic moment from CDMS II experiment

We consider a degenerate or a nearly degenerate dark matter sector where a sizable magnetic moment of a (almost) Dirac type neutral dark matter candidate N is anticipated. Then, due to soft photon exchange, the cross-section in direct detection of N   can be enhanced at low Q²$Q^2$ region. We discuss the implication of this type of models in view of the recent CDMS II report.     

WIMP dark matter in gauge-mediated SUSY breaking models and its phenomenology

We propose an extended version of the gauge-mediated SUSY breaking models where extra SUL₍₂₎$\mathit{SU}{(2)}_L$ doublets and singlet field are introduced. These fields are assumed to be parity-odd under an additional matter parity. In this model, the lightest parity-odd particle among them would be dark matter in the Universe. In this Letter, we discuss direct detection of the dark matter and the collider signatures of the model.     

Neutralino properties from a possible modulation signal in WIMP direct search

We report the main results of a paper by A. Bottino, F. Donato, N. Fornengo and S. Scopel, where the properties of neutralino are analysed under the hypothesis that some preliminary experimental results of the DAMA/NaI Collaboration may be indicative of a yearly modulation effect. The relevant supersymmetric configurations are analysed and the possibility of their investigation by indirect search for relic neutralinos and by accelerator measurements are discussed. It is shown that some of the configurations singled out by the DAMA/NaI results would have cosmological properties compatible with a neutralino as a dominant component of cold dark matter (on the average in the Universe and in our galactic halo).     

Critical revision of the ZEPLIN-I sensitivity to WIMP interactions

The ZEPLIN Collaboration has recently published its first result presenting a maximum sensitivity of 1.1×¹⁰⁻⁶$1.1\times {10}^{\mathrm{-6}}$ picobarn for a WIMP mass of ≈60 GeV$\approx 60\text{ GeV}$. The analysis is based on a discrimination method using the different time distribution of scintillation light generated in electron recoil and nuclear recoil interactions. We show that the methodology followed both for the calibration of the ZEPLIN-I detector response and for the estimation of the discrimination power is not reliable enough to claim any background discrimination at the present stage. The ZEPLIN-I sensitivity appears then to be in the order of 10⁻³ picobarn, three orders of magnitude above the claimed 1.1×¹⁰⁻⁶$1.1\times {10}^{\mathrm{-6}}$ picobarn.     

Development of miracle medicines from sialic acids

Sialic acids are electronegatively charged C9-sugars and are considered to play important roles in higher animals and some microorganisms. Denoting their significance, understanding and exploiting the complexity of the sialic acids has been referred to as the "the third language of life". In essence, "sialic acid derivatives possess a harmonious shape and good balance between two opposing hydrophilic and hydrophobic parts, meaning that they should display various kinds of potentially unique and possibly conflicting physiological activities (glycolipoids)". Consequently, there are good omens that unprecedented 'miracle' medicines could be developed from sialic acid derivatives. In this review, the first problem, the preparation of sialic acids, is covered, the synthesis of sialic acid derivatives and confirmation of their structures obviously being of critical significance. In addition we needed to confirm their precise stereochemistry and a hydrolysis method has been developed for confirmation of the anomeric position. Several of the compounds have already demonstrated interesting bioactivity.     

Predicted Modulated Differential Rates for Direct WIMP Searches at Low Energy Transfers

The differential event rate for direct detection of dark matter,both the time averaged and the modulated one due to the motion of the Earth,are discussed.The calculations focus on relatively light cold dark matter candidates (WIMP) and low energy transfers.It is shown that for sufficiently light WIMPs the extraction of relatively large nucleon cross sections is possible.Furthermore for some WIMP masses the modulation amplitude may change sign,meaning that,in such a case,the maximum rate may occur six months later than naively expected.This effect can be exploited to yield information about the mass of the dark matter candidate,if and when the observation of the modulation of the event rate is established.     

New results of the WIMP search with the first IGEX Ge detectors

To search for cold dark matter (CDM) particles, the data from two (Ge-76 and Ge-natural) detectors, fabricated in the first phase of the IGEX collaboration, were accumulated and analyzed for a period from May 1995 to May 1999. The use of effective passive and active shielding together with pulse shape discrimination allowed us to perform long-term measurements with an energy threshold of 2 keV at a level of the residual background 0.1 counts/(kg keV d). New restrictions on masses of weakly interacting massive particles and the cross section of their elastic scattering on nuclei have been obtained from the data corresponding to 810 d of live time. The derived exclusion plots compete with the best bounds obtained so far. Annual modulations of the CDM signal have been also investigated. It is shown that the planned operation of all IGEX detectors (at Canfranc and Baksan) with the recently achieved low-energy thresholds gives a chance to achieve the DAMA annual modulation sensitivity region in a nearest future.     

Theoretical direct WIMP detection rates for inelastic scattering to excited states

The recent WMAP and Planck data have confirmed that exotic dark matter together with the vacuum energy (cosmological constant) dominate in the flat Universe. Many extensions of the standard model provide dark matter candidates, in particular Weakly Interacting Massive Particles (WIMPs). Thus the direct dark matter detection is central to particle physics and cosmology. Most of the research on this issue has hitherto focused on the detection of the recoiling nucleus. In this paper we study transitions to the excited states, possible in some nuclei, which have sufficiently low lying excited states. Good examples are the first excited states of ¹²⁷I and ¹²⁹Xe. We find appreciable branching ratios for the inelastic scattering mediated by the spin cross sections. So, in principle, the extra signature of the gamma ray following the de-excitation of these states can, in principle, be exploited experimentally.