326 research outputs found
Quantum vacuum and dark matter
Recently, the gravitational polarization of the quantum vacuum was proposed
as alternative to the dark matter paradigm. In the present paper we consider
four benchmark measurements: the universality of the central surface density of
galaxy dark matter haloes, the cored dark matter haloes in dwarf spheroidal
galaxies, the non-existence of dark disks in spiral galaxies and distribution
of dark matter after collision of clusters of galaxies (the Bullet cluster is a
famous example). Only some of these phenomena (but not all of them) can (in
principle) be explained by the dark matter and the theories of modified
gravity. However, we argue that the framework of the gravitational polarization
of the quantum vacuum allows the understanding of the totality of these
phenomena.Comment: Accepted for publication in Astrophysics and Space Scienc
Simulating Turbulence Using the Astrophysical Discontinuous Galerkin Code TENET
In astrophysics, the two main methods traditionally in use for solving the
Euler equations of ideal fluid dynamics are smoothed particle hydrodynamics and
finite volume discretization on a stationary mesh. However, the goal to
efficiently make use of future exascale machines with their ever higher degree
of parallel concurrency motivates the search for more efficient and more
accurate techniques for computing hydrodynamics. Discontinuous Galerkin (DG)
methods represent a promising class of methods in this regard, as they can be
straightforwardly extended to arbitrarily high order while requiring only small
stencils. Especially for applications involving comparatively smooth problems,
higher-order approaches promise significant gains in computational speed for
reaching a desired target accuracy. Here, we introduce our new astrophysical DG
code TENET designed for applications in cosmology, and discuss our first
results for 3D simulations of subsonic turbulence. We show that our new DG
implementation provides accurate results for subsonic turbulence, at
considerably reduced computational cost compared with traditional finite volume
methods. In particular, we find that DG needs about 1.8 times fewer degrees of
freedom to achieve the same accuracy and at the same time is more than 1.5
times faster, confirming its substantial promise for astrophysical
applications.Comment: 21 pages, 7 figures, to appear in Proceedings of the SPPEXA
symposium, Lecture Notes in Computational Science and Engineering (LNCSE),
Springe
Limits on the WIMP-nucleon scattering cross-section from neutrino telescopes
Neutrino-telescopes like Super-Kamiokande and IceCube have started to explore
the neutrino fluxes from WIMP annihilations in the Sun. The non-observation of
a signal can put constraints on the WIMP properties. We here focus on the
neutrino signal from WIMP annihilation in the Sun and show that under
reasonable assumptions, the non-observation of a signal from IceCube puts a
much tighter constraint on the spin-dependent WIMP-proton scattering
cross-section than current direct detection experiments like COUPP and KIMS.
For the spin-independent scattering cross-section, the limits from IceCube and
current direct detection experiments like XENON10 and CDMS place similar
constraints. We here go through the assumptions being made and the
uncertainties that arise in converting from limits on the muon flux from the
Sun to limits on the WIMP-proton cross-section, and present our results as easy
to use conversion factors.Comment: 10 pages, 6 figures. Accepted for publication in JCA
New constraints on the mass of fermionic dark matter from dwarf spheroidal galaxies
Theoretical Physic
Dark Matter Direct Detection Signals inferred from a Cosmological N-body Simulation with Baryons
We extract at redshift z=0 a Milky Way sized object including gas, stars and
dark matter (DM) from a recent, high-resolution cosmological N-body simulation
with baryons. Its resolution is sufficient to witness the formation of a
rotating disk and bulge at the center of the halo potential. The phase-space
structure of the central galactic halo reveals the presence of a dark disk
component, that is co-rotating with the stellar disk. At the Earth's location,
it contributes to around 25% of the total DM local density, whose value is
rho_DM ~ 0.37 GeV/cm^3. The velocity distributions also show strong deviations
from pure Gaussian and Maxwellian distributions, with a sharper drop of the
high velocity tail.
We give a detailed study of the impact of these features on the predictions
for DM signals in direct detection experiments. In particular, the question of
whether the modulation signal observed by DAMA is or is not excluded by limits
set by other experiments (CDMS, XENON and CRESST...) is re-analyzed and
compared to the case of a standard Maxwellian halo, in both the elastic and the
inelastic scattering scenarios. We find that the compatibility between DAMA and
the other experiments is improved. In the elastic scenario, the DAMA modulation
signal is slightly enhanced in the so-called channeling region, as a result of
several effects. For the inelastic scenario, the improvement of the fit is
mainly attributable to the departure from a Maxwellian distribution at high
velocity.Comment: 39 page
Inelastic Dark Matter, Non-Standard Halos and the DAMA/LIBRA Results
The DAMA collaboration have claimed to detect particle dark matter (DM) via
an annual modulation in their observed recoil event rate. This appears to be in
strong disagreement with the null results of other experiments if interpreted
in terms of elastic DM scattering, while agreement for a small region of
parameter space is possible for inelastic DM (iDM) due to the altered
kinematics of the collision. To date most analyses assume a simple galactic
halo DM velocity distribution, the Standard Halo Model, but direct experimental
support for the SHM is severely lacking and theoretical studies indicate
possible significant differences. We investigate the dependence of DAMA and the
other direct detection experiments on the local DM velocity distribution,
utilizing the results of the Via Lactea and Dark Disc numerical simulations. We
also investigate effects of varying the solar circular velocity, the DM escape
velocity, and the DAMA quenching factor within experimental limits. Our data
set includes the latest ZEPLIN-III results, as well as full publicly available
data sets. Due to the more sensitive dependence of the inelastic cross section
on the velocity distribution, we find that with Via Lactea the DAMA results can
be consistent with all other experiments over an enlarged region of iDM
parameter space, with higher mass particles being preferred, while Dark Disc
does not lead to an improvement. A definitive test of DAMA for iDM requires
heavy element detectors.Comment: 22 pages, 10 figures, PDFLaTex Additional analysis of Via Lactea
simulation include
Thermodynamics of an Anyon System
We examine the thermal behavior of a relativistic anyon system, dynamically
realized by coupling a charged massive spin-1 field to a Chern-Simons gauge
field. We calculate the free energy (to the next leading order), from which all
thermodynamic quantities can be determined. As examples, the dependence of
particle density on the anyon statistics and the anyon anti-anyon interference
in the ideal gas are exhibited. We also calculate two and three-point
correlation functions, and uncover certain physical features of the system in
thermal equilibrium.Comment: 18 pages; in latex; to be published in Phys. Rev.
- …