Excluding light asymmetric bosonic dark matter

We argue that current neutron star observations exclude asymmetric bosonic noninteracting dark matter in the range from 2 keV to 16 GeV, including the 5-15 GeV range favored by DAMA and CoGeNT. If bosonic weakly interacting massive particles (WIMPs) are composite of fermions, the same limits apply provided the compositeness scale is higher than ～1012 GeV (for WIMP mass ～1 GeV). In the case of repulsive self-interactions, we exclude the large range of WIMP masses and interaction cross sections which complements the constraints imposed by observations of the Bullet Cluster.     

密度依赖口袋常数下奇异物质的热力学自洽处理及其对混合星性质的影响

在MTT口袋模型的基础上采用密度依赖口袋常数,给出了奇异夸克物质的热力学关系,并用于描述奇异夸克物质及混合星内的夸克相,研究了奇异星、混合星的性质.结果表明,密度依赖口袋常数下,奇异夸克物质的压强公式中有一个附加项,而能量密度中则没有,从而保证了系统的热力学自洽性.在新的热力学关系下,奇异夸克物质的状态方程变软,相应的奇异星的引力质量和对应的半径均变小;混合星的状态方程也变软,其质量变小,而对应的半径也变小.说明经热力学自洽处理后该模型对中子星的状态方程及相应的质量-半径关系等都有显著的影响.     

Equation of state in hybrid stars and the stability window of quark matter

Properties of hybrid stars with a mixed phase composed of asymmetric nuclear matter and strange quark matter are studied. The quark phase is investigated by the quark quasiparticle model with a self-consistent thermodynamic and statistical treatment. We present the stability windows of the strange quark matter with respect to the interaction coupling constant versus the bag constant. We find that the appearance of the quark–hadron mixed phases is associated with the meta-stable or unstable regions of the pure quark matter parameters. The mass–radius relation of the hybrid star is dominated by the equation of state of quark matter rather than nuclear matter. The contour plots of the maximum mass of the hybrid star are shown in the plane of the coupling constant and the bag constant.     

Kaon and antikaon optical potentials in isospin asymmetric hyperonic matter

The medium modifications of the energies of kaons and antikaons in isospin asymmetric hyperonic matter are investigated using a chiral SU(3) model. The isospin-dependent medium effects are important for asymmetric heavy-ion collision experiments, as well as relevant for the neutron star phenomenology as the bulk matter in the interior of the neutron star is highly isospin asymmetric. The effects of hyperons on the medium modifications of the kaons and antikaons in the strange hadronic matter are investigated in the present work and are seen to be appreciable for hadronic matter with large strangeness fractions. The study of the K -mesons in the asymmetric strange hadronic matter can be especially relevant for the compressed strange baryonic matter which can result from asymmetric heavy-ion collision experiments in the future accelerator facility FAIR at GSI.     

Enhancement of dark matter relic density from late time dark matter conversions

We demonstrate that if the dark matter (DM) in the Universe contains multiple components, the possible interactions between the DM components may convert the heavier DM components into lighter ones. It is then possible that the lightest DM component with an annihilation cross section significantly larger than that of the typical weakly interacting massive particle (WIMP) may lead to a relic density in agreement with cosmological observations, due to an enhancement of number density from the DM conversion process at late time after the thermal decoupling. This may provide an alternative source of boost factor relevant to the positron and electron excesses reported by the recent DM indirect search experiments.     

First dark matter limits from a large-mass, low-background, superheated droplet detector

We report on the fabrication aspects and calibration of the first large active mass ( approximately 15 g) modules of SIMPLE, a search for particle dark matter using superheated droplet detectors (SDDs). While still limited by the statistical uncertainty of the small data sample on hand, the first weeks of operation in the new underground laboratory of Rustrel-Pays d'Apt already provide a sensitivity to axially coupled weakly interacting massive particles (WIMPs) competitive with leading experiments, confirming SDDs as a convenient, low-cost alternative for WIMP detection.     

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.     

Review of dark matter direct detection experiments

Matter, as we know it, makes up less than 5% of the Universe. Various astrophysical observations have confirmed that one quarter of the Universe and most of the matter content in the Universe is made up of dark matter. The nature of dark matter is yet to be discovered and is one of the biggest questions in physics. Particle physics combined with astrophysical measurements of the abundance gives rise to a dark matter candidate called weakly interacting massive particle (WIMP). The low density of WIMPs in the galaxies and the extremely weak nature of the interaction with ordinary matter make detection of the WIMP an extraordinarily challenging task, with abundant fakes from various radioactive and cosmogenic backgrounds with much stronger electromagnetic interaction. The extremely weak nature of the WIMP interaction dictates detectors that have extremely low naturally occurring radioactive background, a large active volume (mass) of sensitive detector material to maximize statistics, a highly efficient detector-based rejection mechanism for the dominant electromagnetic background and sophisticated analysis techniques to reject any residual background. This paper reviews currently available major technologies being pursued by various collaborations, with special emphasis on the cryogenic Ge detector technology used by the Cryogenic Dark Matter Search Collaboration (CDMS).     

Neutrino and dark matter physics with sub-keV germanium detectors

Germanium detectors with sub-keV sensitivities open a window to study neutrino physics to search for light weakly interacting massive particle (WIMP) dark matter. We summarize the recent results on spin-independent couplings of light WIMPs from the TEXONO experiment at the Kuo-Sheng Reactor Neutrino Laboratory. Highlights of the physics motivation, our R&D programme, as well as the status and plans are presented.     

Effect of thallium impurities in the DAMA experiment on the allowed parameter space for inelastic dark matter

The inelastic dark matter scenario was proposed to reconcile the DAMA annual modulation with null results from other experiments. In this scenario, weakly interacting massive particles (WIMPs) scatter into an excited state, split from the ground state by an energy δ comparable to the available kinetic energy of a galactic WIMP. We note that for large splittings δ the dominant scattering at DAMA can occur off of thallium nuclei, with A～205, which are present as a dopant at the 10(-3) level in NaI(Tl) crystals. For a WIMP mass mχ≈100 GeV/c2 and δ≈200 keV, we find a region in δ-mχ-parameter space which is consistent with all experiments. These parameters, in particular, can be probed in experiments with thallium in their targets, such as KIMS, but are inaccessible to lighter target experiments. Depending on the tail of the WIMP velocity distribution, a highly modulated signal may or may not appear at CRESST-II.     

Experiments aiming at direct detection of dark matter

We present a review of existing and planned dark matter direct detection experiments. The emphasis is on principle limitations for this detection technique and resulting consequences for future projects. We argue that the near future experiments, CDMS and HDMS, will give such stringent limits on WIMP–nucleon elastic cross sections that the next round of experiments will have to be either massive direction–sensitive detectors or massive ton–scale detectors with almost zero background. Candidate experiments with these requirements are shortly introduced like the newly announced GENIUS proposal. We also shortly discuss the implications of WIMP search results for accelerator experiments and vice versa. Received: 16 April 1998     

Dense stars with exotic configurations

In this paper, we consider dense stars with configurations expected from the SU(3)_C×SU(2)_W× U(1) standard model of strong and electroweak interactions. Following a recent suggestion that strange matter, a form of (uds) quark matter, may be the true ground state of hadronic matter, we investigate the prospect for the existence of dense stars consisting partially, or entirely, of strange matter by comparing the relative stability between neutron matter and strange matter. It is found that the restriction on the maximum star mass holds in all cases, including a pure strange star, a pure neutron star, and a neutron star with a quark core. It is also found that the choice of both the bag constantB and the strong coupling constant _s has a decisive effect on the relative stability between strange matter and neutron matter. For currently accepted values of (B, _s), anA= dense starcannot consist entirely,nor partially, of strange matter. Nevertheless, such conclusion may be subject to change if corrections ofO ( _s ² ) or other effects are taken into account. Finally, we use the framework of Tolman, Oppenheimer, and Volkoff to analyze two cases of boson stars: gluon stars and stars consisting of massive scalar particles (massive bosons). It is found that, in the case of gluon stars, the presence of the bag constant in the QCD vacuum yields results very similar to that found in quark stars. On the other hand, soliton stars consisting of massive bosons exist if there is some background pressure which plays the role similar to the bag constant for lowering the matter pressure. The stability problem for both gluon stars and soliton stars is briefly discussed.     

Properties of quark matter in a new quasiparticle model with QCD running coupling

The running of the QCD coupling in the effective mass causes thermodynamic inconsistency problem in the conventional quasiparticle model. We provide a novel treatment which removes the inconsistency by an effective bag constant. The chemical potential dependence of the renormalization subtraction point is constrained by the Cauchy condition in the chemical potential space. The stability and microscopic properties of strange quark matter are then studied within the completely self-consistent quasiparticle model, and the obtained equation of state of quark matter is applied to the investigation of strange stars. It is found that our improved model can describe well compact stars with mass about two times the solar mass, which indicates that such massive compact stars could be strange stars.     

Dark matter search with the HDMS-experiment and the GENIUS project

We present a new Germanium Dark Matter Experiment. It consists of two HPGe-Detectors which are run in a unique configuration. The anticoincidence between the two detectors will further reduce the background that we achieve now in the Heidelberg-Moscow-Experiment and will allow to improve WIMP cross section limits to a level comparable to planned cryogenic experiments. This should also allow to test recently claimed positive evidence for dark matter by the DAMA experiment.We show first detector performances from the test period in the Heidelberg Low Level Laboratory and give a preliminary estimation for the background reduction efficiency. The HDMS experiment in being built up now in the Gran Sasso Underground Laboratory and will start taking data by the end of this year.For a substantial improvement of the WIMP-nucleon cross section limits, future dark matter experiments will have to be either massive direction-sensitive detectors or massive ton-scale detectors with almost zero background. A proposal for a high mass (1 ton) Ge experiment with a much further reduced background is the Heidelberg GENIUS experiment. GENIUS will be able to give a WIMP limit of the order 0.02 counts/day/kg and additionally to look for the annual modulation WIMP-signature by using raw data without subtraction.     

Dark matter in quantum gravity

We show that quantum gravity, whatever its ultra-violet completion might be, could account for dark matter. Indeed, besides the massless gravitational field recently observed in the form of gravitational waves, the spectrum of quantum gravity contains two massive fields respectively of spin 2 and spin 0. If these fields are long-lived, they could easily account for dark matter. In that case, dark matter would be very light and only gravitationally coupled to the standard model particles.     

Phase transition to color-flavor-locked matter and condensation of Goldstone bosons in neutron star matter

Deconfinement phase transition and condensation of Goldstone bosons in neutron star matter are investigated in a chiral hadronic model (also referred as to the FST model) for the hadronic phase (HP) and in the color-flavor-locked (CFL) quark model for the deconfined quark phase. It is shown that the hadronic-CFL mixed phase (MP) exists in the center of neutron stars with a small bag constant, while the CFL quark matter cannot appear in neutron stars when a large bag constant is taken. Color superconductivity softens the equation of state (EOS) and decreases the maximum mass of neutron stars compared with the unpaired quark matter. The K⁰ condensation in the CFL phase has no remarkable contribution to the EOS and properties of neutron star matter. The EOS and the properties of neutron star matter are sensitive to the bag constant B, the strange quark mass m_s and the color superconducting gap Δ. Increasing B and m_s or decreasing Δ can stiffen the EOS which results in the larger maximum masses of neutron stars.     

奇异星的冷却

从奇异夸克物质的热力学巨势出发计算了奇异星的组份，得到电子丰度随强相互作用耦合常数或奇异物质的密度增大而减小．利用弱电统一理论，推导了奇异物质的中微子能量损失率。通过研究有薄壳的均匀奇异星和中子垦的冷却过程，得到年轻奇异星的表面温度比同年代的中子星的表面温度低得多，这可以作为区别奇异星与中子星的观测途径。 关键词：     

Dark matter seeding and the kinematics and rotation of neutron stars

Self-annihilation of dark matter accreted from the galactic halo in the inner regions of neutron stars may significantly affect their kinematical properties, namely velocity kicks and rotation patterns. We find that if a stable long-lived single or multiple strangelet off-center seed forms leading to an asymmetric ejection of matter and radiation, there is a significant modification in linear and angular momentum observables of the star.     

Dark matter results from 100 live days of XENON100 data

We present results from the direct search for dark matter with the XENON100 detector, installed underground at the Laboratori Nazionali del Gran Sasso of INFN, Italy. XENON100 is a two-phase time-projection chamber with a 62 kg liquid xenon target. Interaction vertex reconstruction in three dimensions with millimeter precision allows the selection of only the innermost 48 kg as the ultralow background fiducial target. In 100.9 live days of data, acquired between January and June 2010, no evidence for dark matter is found. Three candidate events were observed in the signal region with an expected background of (1.8 ± 0.6) events. This leads to the most stringent limit on dark matter interactions today, excluding spin-independent elastic weakly interacting massive particle (WIMP) nucleon scattering cross sections above 7.0 × 10(-45) cm(2) for a WIMP mass of 50 GeV/c(2) at 90% confidence level.     

Vector WIMP miracle

Weakly interacting massive particle (WIMP) is well known to be a good candidate for dark matter, and it is also predicted by many new physics models beyond the standard model at the TeV scale. We found that, if the WIMP is a vector particle (spin-one particle) which is associated with some gauge symmetry broken at the TeV scale, the Higgs mass is often predicted to be 120–125 GeV, which is very consistent with the result of Higgs searches recently reported by ATLAS and CMS Collaborations at the Large Hadron Collider experiment. In this Letter, we consider the vector WIMP using a non-linear sigma model in order to confirm this result as general as possible in a bottom-up approach. Near-future prospects to detect the vector WIMP at both direct and indirect detection experiments of dark matter are also discussed.