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TOPIC: Dark matter
Blobrana


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Dark Matter
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Title: A Signature of Colour-Superconducting Dark Matter?
Authors: K. Lawson

I describe a novel dark matter candidate in which the dark matter is composed of macroscopically large "nuggets" of ordinary quarks and antiquarks in a colour-superconducting phase. The physical properties of these objects are described entirely by QCD and the principles of condensed matter physics. An understanding of these properties allows for predictions of their interactions with the ordinary visible matter of the galaxy and leads to several testable consequences of the model. The spectrum arising from these interactions is entirely fixed by quite general predictions about the structure of dense quark matter and allows for no tuning of parameters. In this talk I present the results of a detailed Thomas-Fermi calculation which demonstrates the plausibility that the annihilation of galactic matter incident on a dark matter nugget may be responsible for both the galactic 511 keV line and a broad MeV scale continuum present in the galactic spectrum measured by COMPTEL.

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Blobrana


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Title: Inelastic Dark Matter and DAMA/LIBRA: An Experimentum Crucis
Authors: Douglas P. Finkbeiner, Tongyan Lin, Neal Weiner

The DAMA/LIBRA collaboration has detected an annual modulation of the recoil rate in NaI crystals with the phase expected for WIMP scattering events. This signal is dramatically inconsistent with upper limits from other experiments for elastically scattering weak-scale WIMPs. However, the results are compatible for the case of inelastic dark matter (iDM). The iDM theory, as implemented by Tucker-Smith and Weiner, constrains the WIMP to a tight contour in sigma_n-delta space, where delta is the mass difference between the ground state and excited WIMPs. An urgent priority in direct detection is to test this scenario. The crucial test of the iDM explanation of DAMA -- an "experimentum crucis" -- is an experiment with directional sensitivity, which can measure the daily modulation in direction. Because the contrast can be 100%, it is a sharper test than the much smaller annual modulation in the rate. We estimate the significance of such an experiment as a function of the WIMP mass, cross section, background rate, and other parameters. The proposed experiment severely constrains the DAMA/iDM scenario even with modest exposure (~1000 kg day) on gaseous xenon.

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Blobrana


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Leptophilic Dark Matter
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Title: High Energy Neutrinos As A Test of Leptophilic Dark Matter
Authors: Douglas Spolyar, Matthew Buckley, Katherine Freese, Dan Hooper, Hitoshi Murayama

Recently, observations by PAMELA, the Fermi Gamma Ray Space Telescope, and other cosmic ray experiments have generated a great deal of interest in dark matter (DM) particles which annihilate at a high rate to leptons. In this letter, we explore the possibility of using large volume neutrino telescopes, such as IceCube, to constrain such models; specifically we consider signals due to DM annihilation in the inner Milky Way. We find that, if Dark Matter annihilations are responsible for the signals observed by PAMELA and FGST, then IceCube (in conjunction with the planned low threshold extension, DeepCore) should detect or exclude the corresponding neutrino signal from the inner Milky Way with a few years of observation.

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Blobrana


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Decaying Dark Matter
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Title: Galactic Signatures of Decaying Dark Matter
Authors: Le Zhang, Guenter Sigl, Javier Redondo
(Version v2)

If dark matter decays into electrons and positrons, it can affect Galactic radio emissions and the local cosmic ray fluxes. We propose a new, more general analysis of constraints on dark matter. The constraints can be obtained for any decaying dark matter model by convolving the specific dark matter decay spectrum with a response function. We derive this response function from full-sky radio surveys at 408 MHz, 1.42 GHz and 23 GHz, as well as from the positron flux recently reported by PAMELA. We discuss the influence of astrophysical uncertainties on the response function, such as from propagation and from the profiles of the dark matter and the Galactic magnetic field. As an application, we find that some widely used dark matter decay scenarios can be ruled out under modest assumptions.

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Blobrana


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Dark matter
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Title: Dark matter bound to the Solar System: consequences for annihilation searches
Authors: Annika H. G. Peter

One method to search for particle dark matter is to hunt down its annihilation products. In the Solar System, three potential types of signals of annihilation have been identified: neutrinos and gamma-rays from the Sun, and neutrinos from the Earth. Each of these signals depends sensitively on the orbital evolution of dark matter once it becomes bound to the Solar System. I will review progress on characterising these signals based on recent improvements in the determination of the properties of the bound dark matter population.

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Blobrana


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You may wonder what's new in astronomy. Over the years, we've learned a lot about the planets, stars and galaxies that one can see in the night sky, but perhaps the most startling discovery is about the stuff that we can't see. This is the "dark matter" that most of the universe seems to be made of.
Thanks largely to Newton and Einstein, we know of many different ways to weigh astronomical objects, even if we can't touch them. Curiously, the masses we measure always far exceed those we gather from measuring the light alone.
This discrepancy has led scientists to hypothesize about the existence of dark matter, and we believe it is an abundant form of matter that permeates the universe, but does not glow.

Source

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Blobrana


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It's certainly the case that 'dark matter', like 'Smurf' or 'government regulation', has in recent times become a de facto explanation for the unexplained.   We aren't big believers in magic so mysterious, undetected forces that explain everything probably actually explain nothing - and tossing out Newton in the process  brings on a higher order of scrutiny, since he has been declared irrelevant often before only to survive quite nicely.
Dark matter is currently unable to reconcile all the current discrepancies between measurements and predictions based on theoretical models and competing theories of gravitation have therefore been developed - their problem is that they conflict with Newton's theory of gravitation.

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Blobrana


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The first tantalising signs of gas within a filament of dark matter have been glimpsed at the site of a cataclysmic collision between galaxy clusters. If future observations confirm the preliminary detection, it would provide an important test of computer simulations that show how large-scale cosmic structures form.
The simulations suggest that matter is distributed in a cosmic web, with material flowing along filamentary structures and pooling where the filaments intersect. Dark matter is thought to act as the scaffolding for this web, and researchers say as much as 40% of all dark matter in the universe may lie in the filaments.

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Blobrana


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Dark matter halo
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Title: A constant dark matter halo surface density in galaxies
Authors: F. Donato, G. Gentile, P. Salucci, C. Frigerio Martins, M. I. Wilkinson, G. Gilmore, E. K. Grebel, A. Koch, R. Wyse

We confirm and extend the recent finding that the central surface density r_0*rho_0 galaxy dark matter halos, where r_0 and rho_0 are the halo core radius and central density, is nearly constant and independent of galaxy luminosity. Based on the co-added rotation curves of about 1000 spiral galaxies, mass models of individual dwarf irregular and spiral galaxies of late and early types with high-quality rotation curves and, galaxy-galaxy weak lensing signals from a sample of spiral and elliptical galaxies, we find that log(r_0*rho_0) = 2.15 ± 0.2, in units of log(Msol/pc˛ ). We also show that the observed kinematics of Local Group dwarf spheroidal galaxies are consistent with this value. Our results are obtained for galactic systems spanning over 14 magnitudes, belonging to different Hubble Types, and whose mass profiles have been determined by several independent methods. In the same objects, the approximate constancy of rho_0*r_0 is in sharp contrast to the systematical variations, by several orders of magnitude, of galaxy properties, including rho_0 and central stellar surface density.

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Blobrana


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Dark Matter
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Title: Inverse Compton constraints on the Dark Matter e+e- excesses
Authors: Marco Cirelli, Paolo Panci

Recent results from experiments like PAMELA have pointed to excesses of e+e- in cosmic rays. If interpreted in terms of Dark Matter annihilations, they imply the existence of an abundant population of e+e- in the galactic halo at large. We consider the high energy gamma ray fluxes produced by Inverse Compton scattering of interstellar photons on such e+e-, and compare them with the available data from EGRET and some preliminary data from FERMI. We consider different observation regions of the sky and a range of DM masses, annihilation channels and DM profiles. We find that large portions of the parameter space are excluded, in particular for DM masses larger than 1 TeV, for leptonic annihilation channels and for benchmark Einasto or NFW profiles.

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