Particle Dark Matter Models Research Articles

Extragalactic Inverse Compton Light from Dark Matter annihilation and the Pamela positron excess

We calculate the extragalactic diffuse emission originating from the up-scattering of cosmic microwave photons by energetic electrons and positrons produced in particle dark matter annihilation events at all redshifts and in all halos. We outline the observational constraints on this emission and we study its dependence on both the particle dark matter model (including the particle mass and its dominant annihilation final state) and on assumptions on structure formation and on the density profile of halos. We find that for low-mass dark matter models, data in the X-ray band provide the most stringent constraints, while the gamma-ray energy range probes models featuring large masses and pair-annihilation rates, and a hard spectrum for the injected electrons and positrons. Specifically, we point out that the all-redshift, all-halo inverse Compton emission from many dark matter models that might provide an explanation to the anomalous positron fraction measured by the Pamela payload severely overproduces the observed extragalactic gamma-ray background.

Bound states of weakly interacting dark matter

We explore the possibility that weakly interacting dark matter can form bound states - WIMPonium. Such states are expected in a wide class of models of particle dark matter, including some limits of the Minimal Supersymmetric Standard Model. We examine the conditions under which we expect bound states to occur, and use analogues of NRQCD applied to heavy quarkonia to provide estimates for their properties, including couplings to the Standard Model. We further find that it may be possible to produce WIMPonium at the LHC, and explore the properties of the WIMP that can be inferred from measurements of the WIMPonium states.

Fitting the gamma-ray spectrum from dark matter with DMFIT: GLAST and the galacticcenter region

We study the potential of GLAST for unveiling particle dark matter properties withgamma-ray observations of the galactic center region. We present full GLASTsimulations including all gamma-ray sources known to date in a region of4° around the galactic center, in addition to the diffuse gamma-ray background and to thedark matter signal. We introduce DMFIT, a tool that allows one to fit gamma-rayemission from pair annihilation of generic particle dark matter models and to extractinformation on the mass, normalization and annihilation branching ratios intoStandard Model final states. We assess the impact and systematic bias inducedby background modeling and theoretical priors on the reconstruction of darkmatter particle properties. Our detailed simulations demonstrate that for some wellmotivated supersymmetric dark matter setups with one year of GLAST data it will bepossible not only to significantly detect a dark matter signal over background,but also to estimate the dark matter mass and its dominant pair annihilationmode.

Searching for Dark Matter with X‐Ray Observations of Local Dwarf Galaxies

A generic feature of weakly interacting massive particle (WIMP) dark matter models is the emission of photons over a broad energy band resulting from the stable yields of dark matter pair annihilation. Inverse Compton scattering off cosmic microwave background photons of energetic electrons and positrons produced in dark matter annihilation is expected to produce significant diffuse X-ray emission. Dwarf galaxies are ideal targets for this type of dark matter search technique, being nearby, dark matter dominated systems free of any astrophysical diffuse X-ray background. In this paper, we present the first systematic study of X-ray observations of local dwarf galaxies aimed at the search for WIMP dark matter. We outline the optimal energy and angular ranges for current telescopes and analyze the systematic uncertainties connected to electron/positron diffusion. We do not observe any significant X-ray excess, and we translate this null result into limits on the mass and pair annihilation cross section for particle dark matter. Our results indicate that X-ray observations of dwarf galaxies currently constrain dark matter models at the same level as or even more strongly than gamma-ray observations of the same systems, although at the expenses of introducing additional assumptions and related uncertainties in the modeling of diffusion and energy loss processes. The limits we find constrain portions of the supersymmetric parameter space, particularly if the effect of dark matter substructures is included. Finally, we comment on the role of future X-ray satellites (e.g., Constellation-X, XEUS) and on their complementarity with GLAST and other gamma-ray telescopes in the quest for particle dark matter.

NEUTRINO MASS AND COLD DARK MATTER PARTICLES IN BIG-BANG NUCLEOSYNTHESIS

Neutrino is a tiny weakly interacting massive particle, but it has strong impacts on various cosmological and astrophysical phenomena. Neutrinos play a critical role in nucleosynthesis of light-to-heavy mass elements in core-collapse supernovae. The light element synthesis is particularly affected by neutrino oscillation (MSW) effect through the ν-process. We propose first that precise determination of sin 2 2θ13 and mass hierarchy can be made by a theoretical study of the observed 7 Li /11 B ratio in stars and presolar grains which are produced from SN ejecta. Theoretical sensitivity in our proposed method is shown to be superior to ongoing long-baseline neutrino experiments for the parameter region 10−4 ≤ sin22θ13 ≤ 10−2. We secondly discuss how to constrain the neutrino mass Σmν from precise analysis of cosmic microwave background anisotropies in the presence of primordial magnetic field. We obtain an upper limit Σmν < 1.3 eV (2σ). Thirdly, we discuss decaying dark-matter particle model in order to solve the primordial lithium problems that the standard Big-Bang nucleosynthesis theory predicts extremely different 6 Li and 7 Li abundances from observations.

Hunting the lightest lightest neutralinos

The lightest neutralino in the minimal supersymmetric extension of the standard model can be, in principle, massless. If superlight neutralinos are the dark matter, structure formation constrains their mass to be above a few keV. I show that relaxing the assumption of radiation domination and entropy conservation prior to big bang nucleosynthesis, the relic abundance of very light neutralinos can be consistent with the inferred cold dark matter density. I study how one can hunt for light neutralino dark matter, with a mass at or below a GeV, focusing on both direct and indirect searches. I argue that the two most promising channels are spin-dependent direct detection and the search for monochromatic gamma rays from the prompt pair-annihilation of neutralinos into photons with GLAST. My study indicates that the lightest lightest neutralinos can be detected as long as their mass is above a few tenth of a GeV, a mass range where a future linear collider could provide important information on the details of the particle dark matter model.

Nonthermal x rays from the Ophiuchus galaxy cluster and dark matter annihilation

We investigate a scenario where the recently discovered nonthermal hard x-ray emission from the Ophiuchus cluster originates from inverse Compton scattering of energetic electrons and positrons produced in weakly interacting dark matter pair annihilations. We show that this scenario can account for both the x ray and the radio emission, provided the average magnetic field is of the order of $0.1\text{ }\text{ }\ensuremath{\mu}\mathrm{G}$. We demonstrate that Gamma-Ray Large Area Telescope (GLAST) will conclusively test the dark matter annihilation hypothesis. Depending on the particle dark matter model, GLAST might even detect the monochromatic line produced by dark matter pair annihilation into two photons.

Models of particle dark matter

Predictions of dark matter detection rates for terrestial detectors are given within the framework of supergravity grand unified models with R parity invariance. These models predict that the lightest neutralino, gc 1 0 should be a component of the cold dark matter over almost the entire parameter space. Relic density calculations are described and the parameter space is limited to 0.1 ≤ Ω gc 1 0 h 2 ≤ 0.4. The effects of recent accelerator experiments (measurements of the top quark mass and b → s + γ decay) on predicted detector event rates is described. Detector event rates are shown to range from about (10 −5 to 10) events/dg da. Effects on the event rates by varying the bounds on Ω gc 1 0 h 2 and from non-universal soft breaking masses are discussed.

Realistic models of supersymmetric particle dark matter

An event reported by CDF has a supersymmetric interpretation consistent with the supersymmetric interpretation of the reported LEP excess of Z → b decays. Together they imply a higgsino LSP of mass about 40 GeV that gives 0.05 ≲ Ωh2 ≲ 1. Its direct detection is discussed. Cold dark matter candidates from a supersymmetric Lagrangian consistent with phenomenological constraints should be called a WISP (for weakly interacting supersymmetric particle); many WIMPs are not WISPs. I also comment on how it is normal in particle theories to have an LSP, massive neutrinos, and of course baryons, so that one automatically has all those forms of matter.