Dark matter and dark matter candidates

The nature and identity of the dark matter of the Universe is one of the most challenging problems facing modern cosmology. Only 5% of the energy density of the Universe can be associated with known forms of matter. Problems for baryonic and neutrino dark matter imply the necessity to search beyond the standard model for dark matter candidates. Emphasis is placed on the prospects for supersymmetric dark matter.     

A molecular probe of dark energy

Many theoretical models of dark energy invoke rolling scaler fields which in turn predict time varying values of the fundamental constants. Establishing the value of the fundamental constants at various times in the universe can probe and test the various dark energy theories. One of the constants that is predicted to vary is the ratio of the electron to proton mass μ. It was established early on that molecular spectra are sensitive to the value of μ and can be used as probes of that value. This article describes the use of the spectrum of molecular hydrogen in high redshift Damped Lyman Alpha systems (DLAs) as a sensitive probe of the time evolution of μ.     

Direct dark matter searches with CDMS and XENON

The cryogenic dark matter search (CDMS) and XENON experiments aim to directly detect dark matter in the form of weakly interacting massive particles (WIMPs) via their elastic scattering on the target nuclei. The experiments use different techniques to suppress background event rates to the minimum, and at the same time, to achieve a high WIMP detection rate. The operation of cryogenic Ge and Si crystals of the CDMS-II experiment in the Soudan mine reported spectrum-weighted exposures of 34 (12) kg-d for the Ge (Si) targets after cuts, over the recoil energies 10–100 keV for a WIMP mass of 60 GeV/c². It gives an upper limit (90% C.L.) of spin-independent WIMP-nucleon cross-section at 1.6 × 10⁻⁴³ cm² for a WIMP mass of 60 GeV/c², starting to constrain predications in supersymmetry models. The two-phase xenon detector of the XENON10 experiment is currently taking data in the Gran Sasso underground lab and promising preliminary results were recently reported. Both experiments are expected to increase their WIMP sensitivity by a one order of magnitude in the scheduled science runs for 2007.     

Antideuteron based dark matter search with GAPS: Current progress and future prospects

The General Antiparticle Spectrometer (GAPS) is a new approach to the indirect detection of dark matter. It relies on searching for primary antideuterons produced in the annihilation of dark matter in the galactic halo. Low energy antideuterons produced through Standard Model processes, such as collisions of cosmic-rays with interstellar baryons, are greatly suppressed compared to primary antideuterons. Thus a low energy antideuteron search provides a clean signature of dark matter. In GAPS antiparticles are slowed down and captured in target atoms. The resultant exotic atom deexcites with the emission of X-rays and annihilation pions, protons and other particles. A tracking geometry allows for the detection of the X-rays and particles, providing a unique signature to identify the mass of the antiparticle. A prototype detector was successfully tested at the KEK accelerator in 2005, and a prototype GAPS balloon flight is scheduled for 2011. This will be followed by a full scale experiment on a long duration balloon from Antarctica in 2014. We discuss the status and future plans for GAPS.     

X-ray measurements of the dark matter distribution in clusters of galaxies with Chandra

We investigate the dark matter distributions in the central region of two clusters of galaxies (A1835 and MKW3S) using Chandra data. N-body simulations in the standard cold dark matter (CDM) model predict the dark matter distribution shows a cuspy dark matter profile: ρ(r) ∝ r, with in the range 1–2, while observations of dwarf and low surface brightness galaxies seem to favor the presence of a relatively flat core: 0 <  < 1. To investigate the dark matter distributions in the central region of clusters of galaxies, we analyze the Chandra data of A1835 and MKW3S with a deprojection method. We derive the mass profiles without the assumption of analytical models. We examine the inner slope of derived mass profiles assuming the dark matter profile is described with a power-law expression. The values of the slope are 0.95 ± 0.10 for A1835 and 1.33 ± 0.12 for MKW3S within the radius of 200 kpc. These are consistent with the result of the CDM simulations. However, within the radius of 100 kpc, the value of is less than unity for A1835 (0.47 ± 0.31). Our result implies that the central dark matter profile of some clusters cannot be described by CDM halos.     

The pGAPS experiment: An engineering balloon flight of prototype GAPS

The General Anti-Particle Spectrometer (GAPS) project is being carried out to search for primary cosmic-ray antiparticles especially for antideuterons produced by cold dark matter. GAPS plans to realize the science observation by Antarctic long duration balloon flights in the late 2010s. In preparation for the Antarctic science flights, an engineering balloon flight using a prototype of the GAPS instrument, “pGAPS”, was successfully carried out in June 2012 in Japan to verify the basic performance of each GAPS subsystem. The outline of the pGAPS flight campaign is briefly reported.     

Role of scalar fields in cosmological models

Recent astronomical observations of supernovae and cosmic microwave background indicate that the universe is accelerating. Scalar–tensor theories of gravity give rise to suitable cosmological models where a late-time accelerated expansion is naturally realized. In an alternative proposal the cosmic acceleration is generated by means of a scalar field (quintessence), in a way similar to the early-time inflation. In this paper, we consider two classes of cosmological models with scalar fields. The first one corresponds to the Jordan–Brans–Dicke tensor–scalar theory with a cosmological scalar and the second one contains a conformally coupled scalar field with quartic potential. In both type of models the cosmological dynamics is described and the deceleration parameter is evaluated. The values of the parameters are specified for which a late-time accelerated expansion is realized.     

Dark Matter Particle Explorer:The First Chinese Cosmic Ray and Hard γ-ray Detector in Space

The Dark Matter Particle Explorer (DAMPE) mission is one of the five scientific space science missions within the framework of the Strategic Pioneer Program on Space Science of the Chinese Academy of Science (CAS) approved in 2011. The main scientific objective of DAMPE is to detect electrons and photons in the range of 5GeV-10TeV with unprecedented energy resolution (1.5% at 100GeV) in order to identify possible Dark Matter (DM) signatures. It will also measure the flux of nuclei up to above 500TeV with excellent energy resolution (40% at 800GeV), which will bring new insights to the origin and propagation high energy cosmic rays. With its excellent photon detection capability, the DAMPE mission is well placed for new discoveries in high energy-ray astronomy as well.      

Dark matter in very poor galaxy groups

We have analyzed a sample of 7000 galaxies in the Local Supercluster (LS) (V < 3100 km/s) selected from the LEDA database [Makarov, D.I., Karachentsev, I.D. A new catalogue of multiple galaxies in the local supercluster small galaxy groups. Small Galaxy Groups ASP Confer. Ser. 209, 40–46, 2000]. We have derived physical properties of poor LS groups selected by dynamical and 3D-Voronoi tessellation methods. Median values of mass-to-luminosity ratios for poor LS groups selected by these methods are 50 M_⊙/L_⊙ and 34 M_⊙/L_⊙, respectively. Physical parameters of LS galaxy triplets in comparison with other samples were evaluated. We suggest that the Dressler effect is present even in such poor groups as galaxy triplets. The data suggest that dark matter haloes are associated with the individual galaxies for LS triplets, which we find are dynamically younger systems. This contrasts with the properties of the Interacting and Northern & Southern triplet samples. For these two samples, the data suggest that the dark matter resides in a common halo. The median values of the mass-to-luminosity ratios for LS triplets, Northern & Southern triplets, and Interacting triplets are 35 M_⊙/L_⊙, 47 M_⊙/L_⊙, and 13 M_⊙/L_⊙, respectively.     

Studying the evolution of the hot universe with the X-ray evolving universe spectroscopy mission – XEUS

Europe is one of the major partners building the International Space Station (ISS) and European industry, together with ESA, is responsible for many station components including the Columbus Orbital Facility, the Automated Transport Vehicle, two connecting modules and the European Robotic Arm. Together with this impressive list of contributions there is a strong desire within the ESA Member States to benefit from this investment by utilizing the unique capabilities of the ISS to perform world-class science. XEUS is one of the astronomical applications being studied by ESA to utilize the capabilities of the ISS. XEUS will be a long-term X-ray observatory with an initial mirror area of 6 m² at 1 keV that will be expanded to 30 m² following a visit to the ISS. The 1 keV spatial resolution is expected to be 2–5″ half-energy-width. XEUS will consist of separate detector and mirror spacecraft (MSC) aligned by active control to provide a focal length of 50 m. A new detector spacecraft, complete with the next generation of instruments, will also be added after visiting the ISS. The limiting 0.1–2.5 keV sensitivity will then be 4 × 10⁻¹⁸ erg cm⁻² s⁻¹, around 200 times better than XMM-Newton, allowing XEUS to study the properties of the hot baryons and dark matter at high redshift.     

QCD-scale modified-gravity universe

A possible gluon-condensate-induced modified-gravity model with f(R) ∝ ∣R∣^1/2 has been suggested previously. Here, a simplified version is presented using the constant flat-spacetime equilibrium value of the QCD gluon condensate and a single pressureless matter component (cold dark matter, CDM). The resulting dynamical equations of a spatially-flat and homogeneous Robertson-Walker universe are solved numerically. This simple empirical model allows, in fact, for a careful treatment of the boundary conditions and does not require a further scaling analysis as the original model did. Reliable predictions are obtained for several observable quantities of the homogeneous model universe. In addition, the estimator E_G, proposed by Zhang et al. to search for deviations from standard Einstein gravity, is calculated for linear sub-horizon matter-density perturbations. The QCD-scale modified-gravity prediction for E_G(z) differs from that of the ΛCDM model by about ±10% depending on the redshift z.     

太阳质子事件与太阳耀斑的关系

通过对0°W-39°W,40°W-70°W,71°W-90°W经度范围内太阳质子事件与太阳耀斑的相关性计算分析,发现太阳质子事件与太阳耀斑的相关系数依赖于经度.太阳耀斑积分与地球磁链接区域（40°W-70°W）太阳质子事件强度的相关系数最大.相关系数的这种特点与耀斑加速粒子的最大流量只出现在磁链接区域的特征相吻合.计算结果表明,太阳耀斑对太阳质子事件具有贡献,即耀斑对E ≥ 10MeV的质子加速有贡献.耀斑和CME在磁链接区域对太阳质子事件的贡献相同,这说明太阳质子事件是混合型事件.     

移位损伤剂量模型及其应用

首先描述了移位损伤的机理及其影响器件性能的机制,引入了适合航天器工程抗辐射加固设计使用的移位损伤剂量模型,探讨了其在CCD器件电荷传输效率CTE,Si器件平均暗电流以太阳电池阵输出功率等工程参数衰降中的应用,介绍了建立的基于移位损伤剂量模型的空间环境中CCD器件CTE衰降预测模式,其结果与欧空局空间环境信息系统的计算结果相吻合．该程序在光电器件抗辐射加固设计中具有重要的应用价值．     

The determination for ideal release point of test masses in drag-free satellites for the detection of gravitational waves

Gravitational waves are ripples in space–time predicted by Albert Einstein's general relativity and provide a new way to understand the universe. Space-borne detectors of gravitational waves, extending to very large scales, can effectively detect the middle and low-frequency gravitational wave source with the frequency band of 0.1 mHz–1 Hz. The test masses are used to make an inertial reference point in the detection of gravitational waves. Currently, there are few studies concerning the ideal release position for the test masses in the detection of gravitational waves. In this study, we give a general solution for test mass release points to minimize the relative motion between the test mass and the satellite mass center. Moreover, we discuss the situation when the release point equation is not satisfied, and the ideal release point of the along-track. Finally, we report on simulations that verify the accuracy of the theoretical derivation.     

The Science Case for STEP

The Satellite Test of the Equivalence Principle (STEP) will advance experimental limits on violations of Einstein’s Equivalence Principle (EP) from their present sensitivity of 2 parts in 10¹³${10}^{13}$ to 1 part in 10¹⁸${10}^{18}$ through multiple comparison of the motions of four pairs of test masses of different compositions in an earth-orbiting drag-free satellite. Dimensional arguments suggest that violations, if they exist, should be found in this range, and they are also suggested by leading attempts at unified theories of fundamental interactions (e.g., string theory) and cosmological theories involving dynamical dark energy. Discovery of a violation would constitute the discovery of a new force of nature and provide a critical signpost toward unification. A null result would be just as profound, because it would close off any possibility of a natural-strength coupling between standard-model fields and the new light degrees of freedom that such theories generically predict (e.g., dilatons, moduli, quintessence). STEP should thus be seen as the intermediate-scale component of an integrated strategy for fundamental physics experiments that already includes particle accelerators (at the smallest scales) and supernova probes (at the largest). The former may find indirect evidence for new fields via their missing-energy signatures, and the latter may produce direct evidence through changes in cosmological equation of state—but only a gravitational experiment like STEP can go further and reveal how or whether such a field couples to the rest of the standard model. It is at once complementary to the other two kinds of tests, and a uniquely powerful probe of fundamental physics in its own right.