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TOPIC: Dark matter
Blobrana


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Title: An upper limit to the central density of dark matter haloes from consistency with the presence of massive central black holes
Authors: X. Hernandez, William H. Lee

We study the growth rates of massive black holes in the centres of galaxies from accretion of dark matter from their surrounding haloes. By considering only the accretion due to dark matter particles on orbits unbound to the central black hole, we obtain a firm lower limit to the resulting accretion rate. We find that a runaway accretion regime occurs on a timescale which depends on the three characteristic parameters of the problem: the initial mass of the black hole, and the volume density and velocity dispersion of the dark matter particles in its vicinity. An analytical treatment of the accretion rate yields results implying that for the largest black hole masses inferred from QSO studies (>10^{9} solar masses), the runaway regime would be reached on time scales which are shorter than the lifetimes of the haloes in question for central dark matter densities in excess of 250 solar masses pc^{-3}. Since reaching runaway accretion would strongly distort the host dark matter halo, the inferences of QSO black holes in this mass range lead to an upper limit on the central dark matter densities of their host haloes of
ho_{0} < 250 solar masses pc^{-3}. This limit scales inversely with the assumed central black hole mass. However, thinking of dark matter profiles as universal across galactic populations, as cosmological studies imply, we obtain a firm upper limit for the central density of dark matter in such structures.

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Blobrana


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Seeking Dark Matter on a Desktop

Desktop experiments could point the way to dark matter discovery, complementing grand astronomical searches and deep underground observations. According to recent theoretical results, small blocks of matter on a tabletop could reveal elusive properties of the as-yet-unidentified dark matter particles that make up a quarter of the universe, potentially making future large-scale searches easier. This finding was announced today by theorists from the Stanford Institute for Materials and Energy Science (SIMES), a joint institute of the Department of Energys SLAC National Accelerator Laboratory and Stanford University, at the American Physical Society meeting in Portland, Oregon.
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Blobrana


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Dark matter could meet its nemesis on Earth

A spinning disc may be all that is needed to overturn Newton's second law of motion - and potentially remove the need for dark matter.
The second law states that a force is proportional to an object's mass and its acceleration. But since the 1980s, some physicists have eyed the law with suspicion, arguing that subtle changes to it at extremely small accelerations could explain the observed motion of stars in galaxies.
Stars move at speeds that suggest that galaxies have far more mass than is visible, which astronomers attribute to dark matter. But if Newton's second law could be modified ever so slightly, it would obviate the need for dark matter. The hypothesis, known as modified Newtonian dynamics (MOND), was proposed in 1981 by Mordehai Milgrom, then at Princeton University.
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Coherent Germanium Neutrino Technology (CoGeNT) collaboration
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Two weeks ago, the CDMSII collaboration published a paper showing that two particles had penetrated its detector's defences - particles that, given the lack of any other particle activity down in the frigid quiet of the detectors, looked very much like dark matter1. Dark matter is thought to make up 85% of the mass in the Universe, but has not been detected directly - quite. The attention-grabbing claim of the CDMSII collaboration has many physicists thinking - but not yet convinced - that the team could be on to something.
Just a stone's throw from the CDMSII experiment, across the subterranean cavern, lies a far smaller box that is thickening the dark-matter plot. The box contains a single germanium hockey puck, similar to those in the CDMSII experiment but operated by the Coherent Germanium Neutrino Technology (CoGeNT) collaboration and tuned to detect incoming particles with much lower masses than the CDMSII. It began collecting data in December 2009, and, after just 56 days, the group is reporting hundreds of particle strikes that cannot be explained other than by invoking dark matter.
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Blobrana


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Dark matter or background noise? Results intriguing but not conclusive

Physicists may have glimpsed a particle that is a leading candidate for mysterious dark matter but say conclusive evidence remains elusive.
A 9-year search from a unique observatory in an old iron mine 2,000 feet underground has yielded two possible detections of weakly interacting massive particles, or WIMPs. But physicists, who include two University of Florida researchers, say there is about a one in four chance that the detections were merely background noise - meaning that a worldwide hunt involving at least two dozen different observatories and hundreds of scientists will continue.
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Blobrana


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Title: New results from DAMA/LIBRA
Authors: R. Bernabei (1,2), P. Belli (2), F. Cappella (3,4), R. Cerulli (5), C.J. Dai (6), A. d'Angelo (3,4), H.L. He (6), A. Incicchitti (4), H.H. Kuang (6), X.H. Ma (6), F. Montecchia (1,2), F. Nozzoli (1,2), D. Prosperi (3,4), X.D. Sheng (6), R.G. Wang (6), Z.P. Ye (6,7) ((1) Univ. Roma Tor Vergata, (2) INFN Roma Tor Vergata, (3) Univ. Roma, (4) INFN Roma, (5) INFN LNGS, (6) IHEP Beijing, (7) Univ. Jing Gangshan)

DAMA/LIBRA is running at the Gran Sasso National Laboratory of the I.N.F.N.. Here the results obtained with a further exposure of 0.34 ton x yr are presented. They refer to two further annual cycles collected one before and one after the first DAMA/LIBRA upgrade occurred on September/October 2008. The cumulative exposure with those previously released by the former DAMA/NaI and by DAMA/LIBRA is now 1.17 ton x yr, corresponding to 13 annual cycles. The data further confirm the model independent evidence of the presence of Dark Matter (DM) particles in the galactic halo on the basis of the DM annual modulation signature (8.9 sigma C.L. for the cumulative exposure). In particular, with the cumulative exposure the modulation amplitude of the single-hit events in the (2 -- 6) keV energy interval measured in NaI(Tl) target is (0.0116 ± 0.0013) cpd/kg/keV; the measured phase is (146 ± 7) days and the measured period is (0.999 ± 0.002) yr, values well in agreement with those expected for the DM particles.

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Blobrana


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Title: A clear Dark Matter gamma ray line generated by the Green-Schwarz mechanism
Authors: Y. Mambrini
(Version v2)

We study the phenomenology of a U_X(1) extension of the Standard Model where the SM particles are not charged under the new abelian group. The Green-Schwarz mechanism insures that the model is anomaly free. The erstwhile invisible dark gauge field X, even if produced with difficulty at the LHC has however a clear signature in gamma-ray telescopes. We investigate what BSM scale (which can be interpreted as a low-energy string scale) would be reachable by the FERMI/GLAST telescope after 5 years of running and show that a 2 TeV scale can be testable, which is highly competitive with the LHC.

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Blobrana


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Title: Dark matter at the centres of galaxies
Authors: David Merritt

A review of the distribution of dark matter on sub-parsec scales at the centers of galaxies.

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Blobrana


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Observations of faint and distant galaxy groups made with the European Space Agency's XMM-Newton observatory have been used to probe the evolution of dark matter. The results of the study are reported in the 20 January issue of The Astrophysical Journal.
Dark matter is a mysterious, invisible constituent of the Universe which only reveals itself through its gravitational influence. Understanding its nature is one of the key open questions in modern cosmology. In one of the approaches used to address this question astronomers use the relationship between mass and luminosity that has been found for clusters of galaxies which links their X-ray emissions, an indication of the mass of the ordinary (baryonic) matter alone, and their total masses (baryonic plus dark matter) as determined by gravitational lensing.
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Title: Shedding Light on the Symmetries of Dark Matter
Authors: Susan Gardner

I consider symmetries which could explain observed properties of dark matter, namely, its stability on Gyr time scales or its relic density and discuss how such symmetries can be discovered through the study of the propagation and polarization of light in its transit through dark matter.

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