Direct Detection of Dark Matter with Resonant Annihilation

In the scenario where the dark matter (DM) particles χχ pair annihilate through a resonance particle R, the constraint from DM relic density makes the corresponding cross section for DM-nuclei elastic scattering extremely small, and can be below the neutrino background induced by the coherent neutrino-nuclei scattering, which makes the DM particle beyond the reach of the conventional DM direct detection experiments. We present an improved analytical calculation of the DM relic density in the case of resonant DM annihilation for s- and p-wave cases and invesitgate the condition for the DM-nuclei scattering cross section to be above the neutrino background. We show that in Higgs-portal type models, for DM particles with s-wave annihilation, the spin-independent DM-nucleus scattering cross section is proportional to Γ_R/m_R, the ratio of the decay width and the mass of R. For a typical DM particle mass ～50 GeV, the condition leads to Γ_R/m_R ≥O(10^-4). In p-wave annihilation case, the spin-independent scattering cross section is insensitive to Γ_R/m_R, and is always above the neutrino background, as long as the DM particle is lighter than the top quark. The real singlet DM model is discussed as a concrete example.     

Direct Detection of Dark Matter with Resonant Annihilation

In the scenario where the dark matter(DM) particles χχˉ pair annihilate through a resonance particle R,the constraint from DM relic density makes the corresponding cross section for DM-nuclei elastic scattering extremely small, and can be below the neutrino background induced by the coherent neutrino-nuclei scattering, which makes the DM particle beyond the reach of the conventional DM direct detection experiments. We present an improved analytical calculation of the DM relic density in the case of resonant DM annihilation for s- and p-wave cases and invesitgate the condition for the DM-nuclei scattering cross section to be above the neutrino background. We show that in Higgs-portal type models, for DM particles with s-wave annihilation, the spin-independent DM-nucleus scattering cross section is proportional to ΓR/mR, the ratio of the decay width and the mass of R. For a typical DM particle mass ～ 50 Ge V,the condition leads to ΓR/mR≥O(10-4). In p-wave annihilation case, the spin-independent scattering cross section is insensitive to ΓR/mR, and is always above the neutrino background, as long as the DM particle is lighter than the top quark. The real singlet DM model is discussed as a concrete example.     

Dark Matter

I review the development of the concept of dark matter. The dark matter story passed through several stages, from a minor observational puzzle to a major challenge for theory of elementary particles. Modern data suggest that dark matter is the dominant matter component in the Universe and that it consists of some unknown non-baryonic particles. Dark matter is the dominant matter component in the Universe; therefore, properties of dark matter particles determine the structure of the cosmic web.     

Tachyonic Dark Matter

Recent attempts to explain the dark matter and energy content of the universe have involved some radical extensions of standard physics, including quintessence, phantom energy, additional space dimensions, and variations in the speed of light. In this paper I consider the possibility that some dark matter might be in the form of tachyons. I show that, subject to some reasonable assumptions, a tachyonic cosmological fluid would produce distinctive effects, such as a surge in quantum vacuum energy and particle creation, and a change in the conventional temperature–time relation for the normal cosmological material. Possible observational consequences are discussed.     

Dark Matter 2013

This article reviews the status of the exciting and fastly evolving field of dark matter research as of summer 2013, when it was discussed at the International Cosmic Ray Conference (ICRC) 2013 in Rio de Janeiro. It focuses on the three main avenues to detect weakly interacting massive particle (WIMP) dark matter: direct detection, indirect detection, and collider searches. The article is based on the dark matter rapporteur talk summarizing the presentations given at the conference, filling some gaps for completeness.     

From Dark Energy &; Dark Matter to Dark Metric

We present a new approach to the mathematical objects of General Relativity in terms of which a generic f(R)-gravity theory gravitation is written in a first-order (à la Palatini) formalism, and introduce the concept of Dark Metric which could bypass the emergence of disturbing concepts as Dark Energy and Dark Matter. These issues are related to the fact that General Relativity could not be the definitive theory of Gravitation due to several shortcomings that come out both from theoretical and experimental viewpoints. At large scales, the attempts to match it with the recent observational data lead to invoke Dark Energy and Dark Matter as the bulk components of the cosmic fluid. Since no final evidence, at fundamental level, exists for such ingredients, it could be useful to reconsider the gravitational sector in order to see if suitable extensions of General Relativity could solve the shortcomings present at infrared scales.     

搜索暗物质

本文前半部分举例说明探测暗星系、星系中的暗物质和暗星,后半部分介绍国际天文界搜索弱相互作用大质量粒子(WIMP)的现状.     

Dark Matter versus Mach's Principle

Empirical and theoretical evidence show that the astrophysical problem of dark matter might be solved by a theory of Einstein-Mayer type. In this theory, up to global Lorentz rotations, the reference system is determined by the motion of cosmic matter. Thus, one is led to a Riemannian space with teleparallelism realizing a geometric version of the Mach-Einstein doctrine. The field equations of this gravitational theory contain hidden matter terms, where the existence of hidden matter is inferred solely from its gravitational effects. It is argued that, in the nonrelativistic mechanical approximation, they provide an inertia-free mechanics, where the inertial mass of a body is induced by the gravitational action of the comic masses. Interpreted from the Newtonian point of view, this mechanics shows that the effective gravitational mass of astrophysical objects depends on r such that one expects the existence of dark matter.     

理解暗能量和暗物质之间的相互作用

从热力学角度研究了暗能量和暗物质之间的相互作用. 假设相互作用是平衡态上的涨落并考虑此涨落导致的熵的修正, 导出了相互作用的物理表述, 把我们模型和观测结果作了比较.     

Anti-deuterons from heavy Dark Matter

We study the fluxes of anti-deuterons that could be produced by annihilations in the galactic halo of Dark Matter particles with multi-TeV mass and a large annihilation cross section, as indicated by the recent PAMELA results. The model of Minimal Dark Matter (MDM) is an example in this category. We find that the fluxes are well within the reach of planned experiments for DM candidates that annihilate mainly into quark pairs, and also extend into the multi-GeV range above the expected astrophysical background. They are instead less promising if the main annihilation channel is into gauge bosons.     

质疑暗物质与暗能量

也许有同志读了本刊今年第2期拙作《暗物质与暗能量》及第4期何祚庥院士的文章《当代物理学正酝酿新的重大突破》后，认为宇宙内广布着暗物质和暗能量已是铁的事实，问题只在于如何进一步探测和确证它们的存在了．其实不然，有一些天文观测