* Astronomy

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RE: Dark matter

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Title: A Search for the Dark Matter Annual Modulation in South Pole Ice
Authors: J. Cherwinka, R. Co, D. F. Cowen, D. Grant, F. Halzen, K. M. Heeger, L. Hsu, A. Karle, V. A. Kudryavtsev, R. Maruyama, W. Pettus, M. Robinson, N. J. C. Spooner

Astrophysical observations and cosmological data have led to the conclusion that nearly one quarter of the Universe consists of dark matter. Under certain assumptions, an observable signature of dark matter is the annual modulation of the rate of dark matter-nucleon interactions taking place in an Earth-bound experiment. To search for this effect, we introduce the concept for a new dark matter experiment using NaI scintillation detectors deployed deep in the South Pole ice. This experiment complements dark matter search efforts in the Northern Hemisphere and will investigate the observed annual modulation in the DAMA/LIBRA and DAMA/NaI experiments. The unique location will permit the study of background effects correlated with seasonal variations and the surrounding environment. This paper describes the experimental concept and explores the sensitivity of a 250 kg NaI experiment at the South Pole.

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New data still have scientists in dark over dark matter

A dark-matter experiment deep in the Soudan mine of Minnesota now has detected a seasonal signal variation similar to one an Italian experiment has been reporting for more than a decade.
The new seasonal variation, recorded by the Coherent Germanium Neutrino Technology (CoGeNT) experiment, is exactly what theoreticians had predicted if dark matter turned out to be what physicists call Weakly Interacting Massive Particles (WIMPs).
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Title: Dark Matter Debris Flows in the Milky Way
Authors: Mariangela Lisanti, David N. Spergel

We show that subhalos falling into the Milky Way create a flow of tidally-stripped debris particles near the galactic center with characteristic velocity behaviour. In the Via Lactea-II N-body simulation, this unvirialized component constitutes a few percent of the local density and has velocities peaked at 340 km/s in the solar neighbourhood. Such velocity substructure has important implications for surveys of low-metallicity stars, as well as direct detection experiments sensitive to dark matter with large scattering thresholds.

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Dark matter no-show confronts supersymmetry

After months of battling radioactive contamination that threatened to swamp its detector, the XENON100 collaboration has managed to place the strongest limits yet on the detection of dark matter. The no-show, announced today at a seminar in Gran Sasso National Laboratory in Italy, places constraints on supersymmetry, the leading alternative to the standard model of particle physics.
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Title: A Novel Method to Extract Dark Matter Parameters from Neutrino Telescope Data
Authors: Arman Esmaili, Yasaman Farzan

Recently it has been shown that when the Dark Matter (DM) particles captured in the Sun directly annihilate into neutrino pairs, the oscillatory terms in the oscillation probability do not average to zero and can lead to a seasonal variation as the distance between the Sun and Earth changes in time. In this paper, we explore this feature as a novel method to extract information on the properties of dark matter. We show that by studying the variation of the flux over a few months, it would in principle be possible to derive the DM mass as well as new information on the flavour structure of the DM annihilation modes. In addition to analytic analysis, we present the results of our numerical calculations that take into account scattering and regeneration of neutrinos traversing the Sun.

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The race to detect dark matter has yielded mostly confusion. But the larger, more sensitive detectors being built could change that picture soon.

Two experiments are independently seeing what seems to be a flux of dark matter streaming through their apparatus. Another detector may have seen a handful of dark-matter particles last year - although the experimenters dismiss them as background noise. And yet another experiment has found no evidence for dark matter at all.
Fortunately, this confusion is likely to be temporary. Dark-matter detectors are roughly 1,000 times more sensitive to ultra-rare events than they were 20 years ago, and that should increase by another factor of 100 over the next decade, as physicists build bigger detectors and become more skilled at suppressing the background noise than can be confused with genuine signals
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Title: Asymmetric WIMP dark matter
Authors: Michael L. Graesser, Ian M. Shoemaker, Luca Vecchi

In existing dark matter models with global symmetries the relic abundance of dark matter is either equal to that of anti-dark matter (thermal WIMP), or vastly larger, with essentially no remaining anti-dark matter (asymmetric dark matter). By exploring the consequences of a primordial asymmetry on the coupled dark matter and anti-dark matter Boltzmann equations we find large regions of parameter space that interpolate between these two extremes. Interestingly, this new asymmetric WIMP framework can accommodate a wide range of dark matter masses and annihilation cross sections. The present-day dark matter population is typically asymmetric, but only weakly so, such that indirect signals of dark matter annihilation are not completely suppressed. We apply our results to existing models, noting that upcoming direct detection experiments will constrain a large region of the relevant parameter space.

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Title: Testing the Warm Dark Matter paradigm with large-scale structures
Authors: Robert E. Smith, Katarina Markovic

We explore the impact of a LWDM cosmological scenario on the clustering properties of large-scale structure in the Universe. We do this by extending the halo model. The new development is that we consider two components to the mass density: one arising from mass in collapsed haloes, and the second from a smooth component of uncollapsed mass. Assuming that the nonlinear clustering of dark matter haloes can be understood, then from conservation arguments one can precisely calculate the clustering properties of the smooth component and its cross-correlation with haloes. We then explore how the three main ingredients of the halo calculations, the mass function, bias and density profiles are affected by WDM. We show that, relative to CDM: the mass function is suppressed by ~50%, for masses ~100 times the free-streaming mass-scale; the bias of low mass haloes can be boosted by up to 20%; core densities of haloes can be suppressed. We also examine the impact of relic thermal velocities on the density profiles, and find that these effects are constrained to scales r<1 kpc/h, and hence of little importance for dark matter tests, owing to uncertainties in the baryonic physics. We use our modified halo model to calculate the non-linear matter power spectrum, and find significant small-scale power in the model. However, relative to the CDM case, the power is suppressed. We then calculate the expected signal and noise that our set of LWDM models would give for a future weak lensing mission. We show that the models should in principle be separable at high significance. Finally, using the Fisher matrix formalism we forecast the limit on the WDM particle mass for a future full-sky weak lensing mission like Euclid or LSST. With Planck priors and using multipoles l<5000, we find that a lower limit of 2.6 keV should be easily achievable.

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Title: Gravitino dark matter and the lithium primordial abundance within a pre-BBN modified expansion
Authors: Sean Bailly
17 Aug 2010

We present supersymmetric scenarios with gravitino LSP and stau NLSP in the case of a non-standard model of cosmology with the addition of a dark component in the pre-BBN era. In the context of the standard model of cosmology, gravitino LSP has drawn quite some attention as it is a good candidate for dark matter. It is produced in scattering processes during reheating after inflation and from the decay of the stau. With a long lifetime, the stau decays during Big Bang Nucleosynthesis. It is strongly constrained by the abundance of light elements but can however address the known ''BBN lithium problem''. It requires fairly massive staus m_tilde tau gtrsim 1TeV and puts an upper bound on the reheating temperature T_R simeq 10^7 GeV which does not satisfy the requirements for thermal leptogenesis. For the non-standard cosmological scenario, the reheating temperature bound can be strongly relaxed TR gg 10^9GeV and the lithium-7 problem solved with a stau typical mass of m_tilde tau ~ 600700 GeV and down to ~ 400GeV with a very important dark component that could enable possible production and detection at the LHC.

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