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TOPIC: Dark matter
Blobrana


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Posts: 131433
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ZEPLIN-III experiment
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Title: Results from the First Science Run of the ZEPLIN-III Dark Matter Search Experiment
Authors: V. N. Lebedenko, H. M. Araujo, E. J. Barnes, A. Bewick, R. Cashmore, V. Chepel, A. Currie, D. Davidge, J. Dawson, T. Durkin, B. Edwards, C. Ghag, M. Horn, A. S. Howard, A. J. Hughes, W. G. Jones, M. Joshi, G. E. Kalmus, A. G. Kovalenko, A. Lindote, I. Liubarsky, M. I. Lopes, R. Luscher, P. Majewski, A. StJ. Murphy, F. Neves, J. Pinto da Cunha, R. Preece, J. J. Quenby, P. R. Scovell, C. Silva, V. N. Solovov, N. J. T. Smith, P. F. Smith, V. N. Stekhanov, T. J. Sumner, C. Thorne, R. J. Walker
(Version v2)

The ZEPLIN-III experiment in the Palmer Underground Laboratory at Boulby uses a 12kg two-phase xenon time projection chamber to search for the weakly interacting massive particles (WIMPs) that may account for the dark matter of our Galaxy. The detector measures both scintillation and ionisation produced by radiation interacting in the liquid to differentiate between the nuclear recoils expected from WIMPs and the electron recoil background signals down to ~10keV nuclear recoil energy. An analysis of 847kg.days of data acquired between February 27th 2008 and May 20th 2008 has excluded a WIMP-nucleon elastic scattering spin-independent cross-section above 8.1x10(-8)pb at 55GeV/c2 with a 90% confidence limit. It has also demonstrated that the two-phase xenon technique is capable of better discrimination between electron and nuclear recoils at low-energy than previously achieved by other xenon-based experiments.

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Blobrana


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Posts: 131433
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Dark Matter
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Title: Dark Matter Through the Neutrino Portal
Authors: Adam Falkowski, Jose Juknevich, Jessie Shelton (Rutgers)

We consider a model of dark matter whose most prominent signature is a monochromatic flux of TeV neutrinos from the galactic center. As an example of a general scenario, we consider a specific model where the dark matter is a fermion in the adjoint representation of a hidden SU(N) gauge group that confines at GeV energies. The absence of light fermionic states in the dark sector ensures stability of dark matter on cosmological time scales. Dark matter couples to the standard model via the neutrino portal, that is, the singlet operator H L constructed from the Higgs and lepton doublets, which is the lowest dimensional fermionic singlet operator in the standard model. This coupling prompts dark matter decay where the dominant decay channel has one neutrino (and at least one dark glueball) in the final state. Other decay channels with charged standard model particles involve more particles in the final state and are therefore suppressed by phase space. In consequence, the standard indirect detection signals like gamma-ray photons, antiprotons and positrons are suppressed with respect to the neutrino signal. This coupling via the neutrino portal is most robustly constrained by Super-Kamiokande, which restricts the dark matter lifetime to be larger than 10^25 seconds. In the near future, the scenario will be probed by the new generation of neutrino telescopes. ANTARES will be sensitive to a dark matter lifetime of order 10^26 seconds, while IceCube/DeepCore can probe a lifetime as large as 10^27 seconds.

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Blobrana


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Integral disproves dark matter origin for mystery radiation
A team of researchers working with data from ESAs Integral gamma-ray observatory has disproved theories that some form of dark matter explains mysterious radiation in the Milky Way.
That this radiation exists has been known since the 1970s, and several theories have been proposed to explain it. Integrals unprecedented spectral and spatial resolution showed that it strongly peaks towards the centre of the Galaxy, with an asymmetry along the Galactic disc.

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Blobrana


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Astrophysicists Solve Mystery in Milky Way Galaxy
A team of astrophysicists has solved a mystery that led some scientists to speculate that the distribution of certain gamma rays in our Milky Way galaxy was evidence of a form of undetectable "dark matter" believed to make up much of the mass of the universe.
In two separate scientific papers, the most recent of which appears in the July 10 issue of the journal Physical Review Letters, the astrophysicists show that this distribution of gamma rays can be explained by the way "antimatter positrons" from the radioactive decay of elements, created by massive star explosions in the galaxy, propagate through the galaxy. Thus, the scientists said, the observed distribution of gamma rays is not evidence for dark matter.

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Blobrana


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Title: Exploring Dark Matter with Milky Way substructure
Authors: M. Kuhlen (IAS, Princeton), P. Madau (UC Santa Cruz), J. Silk (U. of Oxford)
(Version v2)

The unambiguous detection of Galactic dark matter annihilation would unravel one of the most outstanding puzzles in particle physics and cosmology. Recent observations have motivated models in which the annihilation rate is boosted by the Sommerfeld effect, a non-perturbative enhancement arising from a long range attractive force. Here we apply the Sommerfeld correction to Via Lactea II, a high resolution N-body simulation of a Milky-Way-size galaxy, to investigate the phase-space structure of the Galactic halo. We show that the annihilation luminosity from kinematically cold substructure can be enhanced by orders of magnitude relative to previous calculations, leading to the prediction of gamma-ray fluxes from up to hundreds of dark clumps that should be detectable by the Fermi satellite.

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Blobrana


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Title: Capture of dark matter by the Solar System
Authors: I.B.Khriplovich, D.L.Shepelyansky (BINP, Novosibirsk & CNRS, Toulouse)

We study the capture of galactic dark matter by the Solar System. The effect is due to the gravitational three-body interaction between the Sun, one of the planets, and a dark matter particle. The total mass of the captured dark matter particles is found. The estimates for their density are less reliable. The most optimistic of them give an enhancement of dark matter density by about three orders of magnitudes compared to its value in our Galaxy. However, even this optimistic value remains below the best present observational upper limits by about two orders of magnitude.

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Blobrana


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Title: Searching for Dark Matter in Messier 33
Authors: Enrico Borriello, Giuseppe Longo, Gennaro Miele, Maurizio Paolillo, Beatriz B. Siffert, Fatemeh S. Tabatabaei, Rainer Beck

Among various approaches to indirect Dark Matter detection, the study of radio emission due to secondary electrons/positrons produced in WIMPs annihilation and propagating in the galactic magnetic field is arising an increasing interest. In this paper we propose a new method to derive bounds in the <m_chi-sigma_A*v> plane by using radio continuum observations of Messier 33, paying particular attention to a low emitting Radio Cavity. The comparison of the expected radio emission due to the underlying DM distribution with the observed one provides bounds which are comparable to, if not better than, those obtained from a similar analysis of the Milky Way. Remarkably, the present results are simply based on archival data and thus largely improvable by means of specifically tailored observations.

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Blobrana


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WIMP Dark Matter
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Title: Searches for WIMP Dark Matter from the Sun with AMANDA
Authors: James Braun, Daan Hubert, for the IceCube Collaboration

A well-known potential dark matter signature is emission of GeV - TeV neutrinos from annihilation of neutralinos gravitationally bound to massive objects. We present results from recent searches for high energy neutrino emission from the Sun with AMANDA, in all cases revealing no significant excess. We show limits on both neutralino-induced muon flux from the Sun and neutralino-nucleon cross section, comparing them with recent IceCube results. Particularly, our limits on spin-dependent cross section are much better than those obtained in direct detection experiments, allowing AMANDA and other neutrino telescopes to search a complementary portion of MSSM parameter space.

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Blobrana


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Decaying Dark Matter
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Title: The search for decaying Dark Matter
Authors: J.W. den Herder, A. Boyarsky, O. Ruchayskiy, K. Abazajian, C. Frenk, S. Hansen, P. Jonker, C. Kouveliotou, J. Lesgourgues, A. Neronov, T. Ohashi, F. Paerels, S. Paltani, L. Piro, M. Pohl, M. Shaposhnikov, J. Silk, J. Valle

We propose an X-ray mission called Xenia to search for decaying superweakly interacting Dark Matter particles (super-WIMP) with a mass in the keV range. The mission and its observation plan are capable of providing a major break through in our understanding of the nature of Dark Matter (DM). It will confirm, or reject, predictions of a number of particle physics models by increasing the sensitivity of the search for decaying DM by about two orders of magnitude through a wide-field imaging X-ray spectrometer in combination with a dedicated observation program.
The proposed mission will provide unique limits on the mixing angle and mass of neutral leptons, right handed partners of neutrinos, which are important Dark Matter candidates. The existence of these particles is strongly motivated by observed neutrino flavour oscillations and the problem of baryon asymmetry of the Universe.
In super-WIMP models, the details of the formation of the cosmic web are different from those of LambdaCDM. The proposed mission will, in addition to the search for decaying Dark Matter, provide crucial insight into the nature of DM by studying the structure of the "cosmic web". This will be done by searching for missing baryons in emission, and by using gamma-ray bursts as backlight to observe the warm-hot intergalactic media in absorption.

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Blobrana


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Posts: 131433
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Dark Matter
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Size Of A Galaxy Can Be Determined By Its Dark Matter
Dark matter is an enigmatic energy that makes up most of the mass in the Universe, whose nature has not yet been identified. Researchers have succeeded in estimating the percentage of dark matter in the Universe and describing the processes related to the very existence of this matter.
Now, astronomers in the Theoretical Physics and Cosmos Department of the University of Granada, led by Eduardo Battaner, in collaboration with researchers in the Applied Mathematics Department, have made great progress: establishing the distribution and behaviour of the dark matter in a galaxy.
New mathematical calculations on the dark matter describe the density profiles which define how the dark matter changes in a galaxy. This had not been specified in the astronomy field yet. Until now, the behaviour of the dark matter had been estimated through simulations, but the new mathematical description approach based on equations and functions which describe each characteristic of the dark matter make this result much more reliable.

Source University of Granada

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