69 research outputs found
DAMA and the self similar infall halo model
The annual modulation in the rate of WIMP recoils observed by the DAMA
collaboration at high significance is often analyzed in the context of an
isothermal Maxwell-Boltzmann velocity distribution. While this is the simplest
model, there is a need to consider other well motivated theories of halo
formation. In this paper, we study a different halo model, that of self similar
infall which is characterized by the presence of a number of cold streams and
caustics, not seen in simulations. It is shown that the self similar infall
model is consistent with the DAMA result both in amplitude and in phase, for
WIMP masses exceeding 250 GeV at the 99.7% confidence level. Adding a
small thermal component makes the parameter space near = 12 GeV
consistent with the self similar model. The minimum per degree of
freedom is found to be 0.92(1.03) with(without) channeling taken into account,
indicating an acceptable fit. For WIMP masses much greater than the mass of the
target nucleus, the recoil rate depends only on the ratio which is found to be 0.06 femtobarn/TeV. However as in the
case of the isothermal halo, the allowed parameter space is inconsistent with
the null result obtained by the CDMS and Xenon experiments for spin-independent
elastic scattering. Future experiments with directional sensitivity and mass
bounds from accelerator experiments will help to distinguish between different
halo models and/or constrain the contribution from cold flows.Comment: Main conclusions unchanged. Text is expanded, figures and references
added. Accepted for publication in Physical Review D, and this replacement
reflects the final versio
Caustics, cold flows, and annual modulation
We discuss the formation of dark matter caustics, and their possible
detection by future dark matter experiments. The annual modulation expected in
the recoil rate measured by a dark matter detector is discussed. We consider
the example of dark matter particles with a Maxwell-Boltzmann velocity
distribution modified by a cold stream due to a nearby caustic. It is shown
that the effect of the caustic flow is potentially detectable, even when the
density enhancement due to the caustic is small. This makes the annual
modulation effect an excellent probe of inner caustics. We also show that the
phase of the annual modulation at low recoil energies does not constrain the
particle mass unless the velocity distribution of particles in the solar
neighborhood is known.Comment: Minor corrections made, replaced to reflect the published versio
Distinguishing standard reionization from dark matter models
The Wilkinson Microwave Anisotropy Probe (WMAP) experiment has detected
reionization at the level and has reported a mean optical depth of
. A powerful probe of reionization is the large-angle
polarization power spectrum, which is now (since the first five years of data
from WMAP) cosmic variance limited for . Here we consider partial
reionization caused by WIMP dark matter annihilation, and calculate the
expected polarization power spectrum. We compare the dark matter models with a
standard 2-step reionization theory, and examine whether the models may be
distinguished using current, and future CMB observations. We consider dark
matter annihilation at intermediate redshifts () due to halos, as well as
annihilation at higher redshifts due to free particles. In order to study the
effect of high redshift dark matter annihilation on CMB power spectra, it is
essential to include the contribution of residual electrons (left over from
recombination) to the ionization history. Dark matter halos at redshifts
influence the low multipoles in the power spectrum, while the
annihilation of free particle dark matter at high redshifts mainly
affects multipoles .Comment: Minor corrections. Published in Phys. Rev. Replaced to reflect the
published versio
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