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TOPIC: Dark matter
Blobrana


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Cosmic-ray positrons
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Title: Diffuse gamma-ray background and cosmic-ray positrons from annihilating dark matter
Authors: Masahiro Kawasaki, Kazunori Kohri, Kazunori Nakayama

We study the annihilating dark matter contribution to the extra-galactic diffuse gamma-ray background spectrum, motivated by the recent observations of cosmic-ray positron/electron anomalies. The observed diffuse gamma-ray flux provides stringent constraint on dark matter models and we present upper bounds on the annihilation cross section of the dark matter. It is found that for the case of cored dark matter halo profile, the diffuse gamma-rays give more stringent bound compared with gamma-rays from the Galactic center. The Fermi satellite will make the bound stronger.

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Blobrana


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Dark Matter
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Title: Notes on Hidden Mirror World
Authors: Sergei I. Blinnikov (ITEP and IPMU)

A few remarks on Dark Matter (DM) models are presented. An example is Mirror Matter which is the oldest but still viable DM candidate, perhaps not in the purest form. It can serve as a test-bench for other analogous DM models, since the properties of macroscopic objects are quite firmly fixed for Mirror Matter. A pedagogical derivation of virial theorem is given and it is pointed out that concepts of virial velocity or virial temperature are misleading for some cases. It is shown that the limits on self-interaction cross-sections derived from observations of colliding clusters of galaxies are not real limits for individual particles if they form macroscopic bodies. The effect of the heating of interstellar medium by Mirror Matter compact stars is very weak but may be observable. The effect of neutron star heating by accretion of M-baryons may be negligible. Problems of MACHOs as Mirror Matter stars are touched upon.

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Blobrana


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Dark matter could come naturally from quantum gravity.
Physicist looks at 'effective field theory' to explain the mysterious entity.

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Blobrana


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RE: Positron Excess
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Title: Astrophysical Uncertainties in the Cosmic Ray Electron and Positron Spectrum From Annihilating Dark Matter
Authors: Melanie Simet, Dan Hooper

In recent years, a number of experiments have been conducted with the goal of studying cosmic rays at GeV to TeV energies. This is a particularly interesting regime from the perspective of indirect dark matter detection. To draw reliable conclusions regarding dark matter from cosmic ray measurements, however, it is important to first understand the propagation of cosmic rays through the magnetic and radiation fields of the Milky Way. In this paper, we constrain the characteristics of the cosmic ray propagation model through comparison with observational inputs, including recent data from the CREAM experiment, and use these constraints to estimate the corresponding uncertainties in the spectrum of cosmic ray electrons and positrons from dark matter particles annihilating in the halo of the Milky Way.

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Blobrana


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Title: Positron Excess, Luminous-Dark Matter Unification and Family Structure
Authors: Paul H. Frampton, Pham Q. Hung
(Version v3)

It is commonly assumed that dark matter may be composed of one or at most a few elementary particles. PAMELA data present a window of opportunity into a possible relationship between luminous and dark matter. Along with ATIC data the two positron excesses are interpreted as a reflection of dark matter family structure. In a unified model it is predicted that at least a third enhancement might show up at a different energy. The strength of the enhancements however depends on interfamily mixing angles.

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Blobrana


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Dark Matter Candidates
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Title: Dark Matter Candidates
Authors: Lars Bergstrom
(Version v3)

An overview is given of various dark matter candidates. Among the many suggestions given in the literature, axions, inert Higgs doublet, sterile neutrinos, supersymmetric particles and Kaluza-Klein particles are discussed. The situation has recently become very interesting with new results on antimatter in the cosmic rays having dark matter as one of the leading possible explanations. Problems of this explanation and possible solutions are discussed, and the importance of new measurements is emphasized. If the explanation is indeed dark matter, a whole new field of physics, with unusual although not impossible mass and interaction properties may soon open itself to discovery.

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Blobrana


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RE: Dark matter
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Title: Is There a Dark Matter Signal in the Galactic Positron Annihilation Radiation?
Authors: R.E. Lingenfelter, J.C. Higdon, R.E. Rothschild

Assuming Galactic positrons do not go far before annihilating, a difference between the observed 511 keV annihilation flux distribution and that of positron production, expected from beta-plus decay in Galactic iron nucleosynthesis, was evoked as evidence of a new source and a signal of dark matter. We show, however, that the dark mater sources can not account for the observed positronium fraction without extensive propagation. Yet with such propagation, standard nucleosynthetic sources can fully account for the spatial differences and the positronium fraction, leaving no signal for dark mater to explain.

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Blobrana


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A 10-year study of 100,000 galaxies close to our own offers compelling proof that long-hypothesized "dark matter" does exist and is in fact a guiding force behind the structure of the universe, a team of Australian, British, and American astronomers revealed this week.

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Blobrana


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When it comes to finding dark matter in space, astronomers need to go on sort of a ghost hunt. Dark matter can't be directly seen or isolated in a laboratory. Yet it makes up the bulk of the matter in the universe. It is the invisible scaffolding for the formation of stars and galaxies. Dark matter is not made of the same stuff that stars, planets, and people are made of. That stuff is normal "baryonic" matter, consisting of electrons, protons, and neutrons. For 80 years astronomers have known about dark matter's "ghostly" pull on normal matter. They've known that without the gravitational "glue" of dark matter galaxy clusters would fly apart, and even galaxies would have a hard time holding together.
Now the Hubble Space Telescope has uncovered a strong new line of evidence that galaxies are embedded in halos of dark matter. Peering into the tumultuous heart of the nearby Perseus galaxy cluster, Hubble's sharp view resolved a large population of small galaxies that have remained intact while larger galaxies around them are being ripped apart by the gravitational tug of other galaxies. The dwarfs' "invisible shield" is a robust halo of dark matter that keeps them intact despite a several-billion-year-long bumper-car game inside the massive galaxy cluster.

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Blobrana


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Title: Detailed dark matter maps of galaxy cluster substructure and direct comparison to simulations
Authors: Dan Coe

Images from the next generation of telescopes will enable strikingly detailed reconstruction of the dark matter distributions in galaxy cluster cores using strong gravitational lensing analysis. This will provide a key test of Lambda-CDM cosmology on cluster scales where tensions currently exist. Observed dark matter distributions will be compared directly to those realised in simulations, forgoing any assumptions about light tracing mass. The required observations are deep, multicolour, and high-resolution, ideally supplemented with spectra of faint objects. ACS onboard HST is capable of obtaining images of sufficient quality, but for prohibitive integration times. The next generation of telescopes promises to efficiently yield the required images. An analysis method capable of processing the expected large numbers of multiple images has been developed. The full range of constraints possible from analysing these detailed mass maps is a matter of ongoing investigation.

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