On the use of X-ray and γ-ray telescopes for identifying the origin of electrons and positrons observed by ATIC, Fermi, and PAMELA

X-ray and γ-ray observations can help understand the origin of the electron and positron signals reported by ATIC, PAMELA, PPB-BETS, and Fermi. It remains unclear whether the observed high-energy electrons and positrons are produced by relic particles, or by some astrophysical sources. To distinguish between the two possibilities, one can compare the electron population in the local neighborhood with that in the dwarf spheroidal galaxies, which are not expected to host as many pulsars and other astrophysical sources. This can be accomplished using X-ray and γ-ray observations of dwarf spheroidal galaxies. Assuming the signal detected by Fermi and ATIC comes from dark matter and using the inferred dark matter profile of the Draco dwarf spheroidal galaxy as an example, we calculate the photon spectrum produced by electrons via inverse Compton scattering. Since little is known about the magnetic fields in dwarf spheroidal galaxies, we consider the propagation of charged particles with and without diffusion. Extending the analysis of Fermi collaboration for Draco, we find that for a halo mass ∼10⁹ M_⊙, even in the absence of diffusion, the γ-ray signal would be above the upper limits. This conclusion is subject to uncertainties associated with the halo mass. If dwarf spheroidal galaxies host local magnetic fields, the diffusion of the electrons can result in a signal detectable by future X-ray telescopes.     

Optimized running conditions and sensitivity for direction sensitive detectors of WIMP dark matter

Optimum fill pressures for direction-sensitive dark matter detectors based on tracking in gases are considered. Given the minimum resolvable track length and the gas fill, the Lindhard–Scharf stopping model leads to the existence of an optimum pressure which maximizes the specific event rate R (event rate per unit detector volume). In addition, maximizing the detectibility of the recoil nucleus diurnal asymmetry is considered. Optimum fill pressures are calculated for Ar, CF₄, CS₂ and Xe gas fills, as a function of the WIMP mass and the minimum resolvable track length. The associated minimum target volumes required to achieve currently competitive WIMP-nucleon cross-section sensitivity are also calculated. The standard isothermal sphere model of the galactic WIMP halo is used throughout, but the method could be extended to use any desired WIMP distribution function.     

银河系卫星星系研究进展

对银河系内卫星星系进行全面的"人口普查"具有重要的意义。目前已经发现了二十几个卫星星系,其光度范围分布很广,最暗的矮星系比球状星体还暗。叙述了卫星星系的光度分布、空间分布和动力学性质。总结了观测和理论研究进展,并讨论了星流和伽玛射线在研究银河系结构和暗物质性质方面的贡献。表明了卫星星系的统计分布能用来很好地限制冷暗物质理论和星系形成的相关物理过程,同时指出当前研究的局限性和可能的发展方向。     

Numerical modelling of the vertical structure and dark halo parameters in disc galaxies

The non‐linear dynamics of bending instability and vertical structure of a galactic stellar disc embedded into a spherical halo are studied with N‐body numerical modelling. Development of the bending instability in stellar galactic disc is considered as the main factor that increases the disc thickness. Correlation between the disc vertical scale height and the halo‐to‐disc mass ratio is predicted from the simulations. The method of assessment of the spherical‐to‐disc mass ratio for edge‐on spiral galaxies with a small bulge is considered. Modelling of eight edge‐on galaxies: NGC 891, NGC 4738, NGC 5170, UGC 6080, UGC 7321, UGC 8286, UGC 9422 and UGC 9556 is performed. Parameters of stellar discs, dark haloes and bulges are estimated. The lower limit of the dark‐to‐luminous mass ratio in our galaxies is of the order of one within the limits of their stellar discs. The dark haloes dominate by mass in the galaxies with very thin stellar discs (NGC 5170, UGC 7321 and UGC 8286) (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Metallicity and kinematical clues to the formation of the Local Group

The kinematics and elemental abundances of resolved stars in the nearby Universe can be used to infer conditions at high redshift, trace how galaxies evolve and constrain the nature of dark matter. This approach is complementary to direct study of systems at high redshift, but I will show that analysis of individual stars allows one to break degeneracies, such as between star formation rate and stellar Initial Mass Function, that complicate the analysis of unresolved, distant galaxies (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Primordial black holes

Primordial black holes (PBHs) are a profound signature of primordial cos-mological structures and provide a theoretical tool to study nontrivial physics of the early Universe. The mechanisms of PBH formation are discussed and observational constraints on the PBH spectrum, or effects of PBH evaporation, are shown to re-strict a wide range of particle physics models, predicting an enhancement of the ul-traviolet part of the spectrum of density perturbations, early dust-like stages, first or-der phase transitions and stages of superheavy metastable particle dominance in the early Universe. The mechanism of closed wall contraction can lead, in the inflation-ary Universe, to a new approach to galaxy formation, involving primordial clouds of massive BHs created around the intermediate mass or supermassive BH and playing the role of galactic seeds.     

A possible explanation for the electron/positron excess of ATIC/PAMELA

Results from PAMELA and ATIC indicate that the Kaluza-Klein type dark matter particles could be the annihilation source of the observed excess of electrons and positrons.Assuming the existence of a nearby black hole with 10000–100000 solar masses and a point source boost algorithm,we apply the standard propagation model and find that the results fit the data well.     

吐哈盆地十红滩铀矿床铀源条件

以吐哈盆地十红滩砂岩型铀矿床为例,利用U-Pb同位素体系演化特征,计算含矿砂岩和顶底板泥岩的原始铀质量分数及变化系数,认为赋矿地层沉积时就存在铀的预富集,同生沉积碎屑岩和泥岩都是本区重要的铀源。结合古水文地质演化和碳-氧同位素特征,认为成岩期泥岩压榨水携带铀进入砂岩含水层,在砂岩中产生铀的预富集。     

辽河西部凹陷欢喜岭地区沙河街组层序界面的识别

对辽河西部凹陷欢喜岭地区层序地层的研究,总结出4种层序界面的识别方法:①钻井、测井资料;②泥砂比曲线;③小波变换;④地震时频分析。方法①表现为在沙河街组各三级层序界面处,岩性、相序、曲线形态和幅值有不同程度的突变;方法②表现为在一个完整的三级层序中,泥砂比曲线由小变大再变小,其中泥砂比值最大处为最大湖泛面(MFS)位置;方法③表现为在一个完整的三级层序中,谱系图从低频到高频再到低频的变化,在系数曲线上表现为一个或近似一个完整的振荡旋回,其中谱系图中高频部分对应着最大湖泛面位置;方法④在剖面上层序界面处为低频部分,高频部分是最大湖泛面位置。通过测井与地震信息相结合,综合运用4种方法识别出7个层序界面和6个最大湖泛面,由此建立了研究区的高精度层序地层格架。     

长白山区暗棕壤成土作用地球化学特征

以代表性暗棕壤垂直剖面土壤地球化学数据为依据,研究了长白山区特定的森林景观条件下成土过程中元素的分异与富集特征。研究结果表明,在岩石风化过程中主要以CaO、 Na2 O、 Sr淋溶为主,有机酸淋溶过程中SiO2、 Al2 O3、 K2 O部分被淋溶,部分游离铁下渗到土体中下部氧化成铁锰胶膜;微量元素在风化过程中被次生黏土矿物吸附,不同程度地富集,在腐殖质积累过程中Cd、 Zn、Pb、 Mo、 Hg、 Co、 Mn、 Cr等亲生物元素进一步富集于表层土壤, Ce、 Ni、 Sb、 Ti、 V、 Y、 Zr在表生环境中地球化学性质稳定,残留富集于土壤表层。母质层继承和保留了基岩元素地球化学分布的基本特征。