* Astronomy

Title: Testing The Light Dark Matter Hypothesis With AMS
Authors: Dan Hooper, Wei Xue

The spectrum and morphology of gamma-rays from the Galactic Center and the spectrum of synchrotron emission observed from the Milky Way's radio filaments have each been interpreted as possible signals of \sim 7-10 GeV dark matter particles annihilating in the Inner Galaxy. In dark matter models capable of producing these signals, the annihilations should also generate significant fluxes of \sim 7-10 GeV positrons which can lead to a distinctive bump-like feature in local cosmic ray positron spectrum. In this letter, we show that while such a feature would be difficult to detect with PAMELA, it would likely be identifiable by the currently operating AMS experiment. As no known astrophysical sources or mechanisms are likely to produce such a sharp feature, the observation of a positron bump at around 7-10 GeV would significantly strengthen the case for a dark matter interpretation of the reported gamma-ray and radio anomalies.

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Title: Can Effects of Dark Matter be Explained by the Turbulent Flow of Spacetime?
Authors: F. Elliott Koch, Angus H. Wright

For the past forty years the search for dark matter has been one of the primary foci of astrophysics, although there has yet to be any direct evidence for its existence (Porter et al. 2011). Indirect evidence for the existence of dark matter is largely rooted in the rotational speeds of stars within their host galaxies, where, instead of having a ~ r^½ radial dependence, stars appear to have orbital speeds independent of their distance from the galactic center, which led to proposed existence of dark matter (Porter et al. 2011; Peebles 1993). We propose an alternate explanation for the observed stellar motions within galaxies, combining the standard treatment of a fluid-like spacetime with the possibility of a "bulk flow" of mass through the Universe. The differential "flow" of spacetime could generate vorticies capable of providing the "perceived" rotational speeds in excess of those predicted by Newtonian mechanics. Although a more detailed analysis of our theory is forthcoming, we find a crude "order of magnitude" calculation can explain this phenomena. We also find that this can be used to explain the graviational lensing observed around globular clusters like "Bullet Cluster".

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Ed ~ Unfortunately, these 'Spacetime vorticies' would be detected by looking at the light from distant quasars and measuring the time-lag effect (which has already been done). 

Title: A new determination of the local dark matter density from the kinematics of K dwarfs
Authors: Silvia Garbari, Chao Liu, Justin I. Read, George Lake
(Version, v2)

We apply a new method to determine the local disc matter and dark halo matter density to kinematic and position data for \sim2000 K dwarf stars taken from the literature. Our method assumes only that the disc is locally in dynamical equilibrium, and that the 'tilt' term in the Jeans equations is small up to \sim1 kpc above the plane. We present a new calculation of the photometric distances to the K dwarf stars, and use a Monte Carlo Markov Chain to marginalise over uncertainties in both the baryonic mass distribution, and the velocity and distance errors for each individual star. We perform a series of tests to demonstrate that our results are insensitive to plausible systematic errors in our distance calibration, and we show that our method recovers the correct answer from a dynamically evolved N-body simulation of the Milky Way. We find a local dark matter density of {rho}dm = 0.025+0.014-0.013 solar masses pc^{-3} (0.95+0.53-0.49 GeV cm^{-3}) at 90% confidence assuming no correction for the non-flatness of the local rotation curve, and {rho}dm = 0.022+0.015-0.013 solar masses pc^-3 (0.85+0.57-0.50 GeV cm^{-3}) if the correction is included. Our 90% lower bound on {rho}dm is larger than the canonical value typically assumed in the literature, and is at mild tension with extrapolations from the rotation curve that assume a spherical halo. Our result can be explained by a larger normalisation for the local Milky Way rotation curve, an oblate dark matter halo, a local disc of dark matter, or some combination of these.

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Title: Search for a dark matter particle family
Authors: Yukio Tomozawa

I suggest a simple signature for new particles which are unstable partners of a dark matter particle. The suggested mass range is from 8 TeV to 3 PeV, the former being the mass of the dark matter particle and the latter being the knee energy mass scale from the cosmic ray energy spectrum. It can be the energy spectrum of a specific particle such as a muon, a neutrino, jets or any other particles produced in cosmic ray showers, as long as the spectrum is measured. As for the detection of a 3 PeV particle by the neutrino energy spectrum, all dark matter targets throughout the galaxy that are bombarded by high energy cosmic rays and high energy dark matter particles contribute to the process. This is new in the study of dark matter physics.

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