538 research outputs found
Baryon Destruction by Asymmetric Dark Matter
We investigate new and unusual signals that arise in theories where dark
matter is asymmetric and carries a net antibaryon number, as may occur when the
dark matter abundance is linked to the baryon abundance. Antibaryonic dark
matter can cause {\it induced nucleon decay} by annihilating visible baryons
through inelastic scattering. These processes lead to an effective nucleon
lifetime of 10^{29}-10^{32} years in terrestrial nucleon decay experiments, if
baryon number transfer between visible and dark sectors arises through new
physics at the weak scale. The possibility of induced nucleon decay motivates a
novel approach for direct detection of cosmic dark matter in nucleon decay
experiments. Monojet searches (and related signatures) at hadron colliders also
provide a complementary probe of weak-scale dark-matter--induced baryon number
violation. Finally, we discuss the effects of baryon-destroying dark matter on
stellar systems and show that it can be consistent with existing observations.Comment: 26 pages, 6 figure
Dark Matter Antibaryons from a Supersymmetric Hidden Sector
The cosmological origin of both dark and baryonic matter can be explained
through a unified mechanism called hylogenesis where baryon and antibaryon
number are divided between the visible sector and a GeV-scale hidden sector,
while the Universe remains net baryon symmetric. The "missing" antibaryons, in
the form of exotic hidden states, are the dark matter. We study model-building,
cosmological, and phenomenological aspects of this scenario within the
framework of supersymmetry, which naturally stabilizes the light hidden sector
and electroweak mass scales. Inelastic dark matter scattering on visible matter
destroys nucleons, and nucleon decay searches offer a novel avenue for the
direct detection of the hidden antibaryonic dark matter sea.Comment: 33 pages, 10 figures. Minor changes to match published versio
Cosmic 21-cm Delensing of Microwave Background Polarization and the Minimum Detectable Energy Scale of Inflation
The curl (B) modes of cosmic microwave background (CMB) polarization
anisotropies are a unique probe of the primordial background of inflationary
gravitational waves (IGWs). Unfortunately, the B-mode polarization anisotropies
generated by gravitational waves at recombination are confused with those
generated by the mixing of gradient-mode (E-mode) and B-mode polarization
anisotropies as CMB photons propagate through the Universe and are
gravitationally lensed. We describe here a method for delensing CMB
polarization anisotropies using observations of anisotropies in the cosmic
21-cm radiation emitted or absorbed by neutral hydrogen atoms at redshifts 10
to 200. While the detection of cosmic 21-cm anisotropies at high resolution is
challenging, a combined study with a relatively low-resolution (but
high-sensitivity) CMB polarization experiment could probe inflationary energy
scales well below the Grand Unified Theory (GUT) scale of 10^{16} GeV --
constraining models with energy scales below 10^{15} GeV (the detectable limit
derived from CMB observations alone). The ultimate theoretical limit to the
detectable inflationary energy scale via this method may be as low as 3 \times
10^{14} GeV.Comment: 4 pages, 2 figures, submitted to Phys. Rev. Let
Measuring the Primordial Deuterium Abundance During the Cosmic Dark Ages
We discuss how measurements of fluctuations in the absorption of cosmic
microwave background (CMB) photons by neutral gas during the cosmic dark ages,
at redshifts z ~ 7--200, could reveal the primordial deuterium abundance of the
Universe. The strength of the cross-correlation of brightness-temperature
fluctuations due to resonant absorption of CMB photons in the 21-cm line of
neutral hydrogen with those due to resonant absorption of CMB photons in the
92-cm line of neutral deuterium is proportional to the fossil deuterium to
hydrogen ratio [D/H] fixed during big bang nucleosynthesis (BBN). Although
technically challenging, this measurement could provide the cleanest possible
determination of [D/H], free from contamination by structure formation
processes at lower redshifts, and has the potential to improve BBN constraints
to the baryon density of the Universe \Omega_{b} h^2. We also present our
results for the thermal spin-change cross-section for deuterium-hydrogen
scattering, which may be useful in a more general context than we describe
here.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Let
Cosmological Signatures of Interacting Neutrinos
We investigate signatures of neutrino scattering in the Cosmic Microwave
Background (CMB) and matter power spectra, and the extent to which present
cosmological data can distinguish between a free streaming or tightly coupled
fluid of neutrinos. If neutrinos have strong non-standard interactions, for
example, through the coupling of neutrinos to a light boson, they may be kept
in equilibrium until late times. We show how the power spectra for these models
differ from more conventional neutrino scenarios, and use CMB and large scale
structure data to constrain these models. CMB polarization data improves the
constraints on the number of massless neutrinos, while the Lyman--
power spectrum improves the limits on the neutrino mass. Neutrino mass limits
depend strongly on whether some or all of the neutrino species interact and
annihilate. The present data can accommodate a number of tightly-coupled
relativistic degrees of freedom, and none of the interacting-neutrino scenarios
considered are ruled out by current data -- although considerations regarding
the age of the Universe disfavor a model with three annihilating neutrinos with
very large neutrino masses.Comment: 17 pages, 14 figures, minor changes and references added, published
in Phys. Rev.
Polarizing Bubble Collisions
We predict the polarization of cosmic microwave background (CMB) photons that
results from a cosmic bubble collision. The polarization is purely E-mode,
symmetric around the axis pointing towards the collision bubble, and has
several salient features in its radial dependence that can help distinguish it
from a more conventional explanation for unusually cold or hot features in the
CMB sky. The anomalous "cold spot" detected by the Wilkinson Microwave
Anisotropy Probe (WMAP) satellite is a candidate for a feature produced by such
a collision, and the Planck satellite and other proposed surveys will measure
the polarization on it in the near future. The detection of such a collision
would provide compelling evidence for the string theory landscape.Comment: Published version. 15 pages, 8 figure
Chronic wasting disease prions are not transmissible to transgenic mice overexpressing human prion protein
Chronic wasting disease (CWD) is a prion disease that affects free-ranging and captive cervids, including mule deer, white-tailed deer, Rocky Mountain elk and moose. CWD-infected cervids have been reported in 14 USA states, two Canadian provinces and in South Korea. The possibility of a zoonotic transmission of CWD prions via diet is of particular concern in North America where hunting of cervids is a popular sport. To investigate the potential public health risks posed by CWD prions, we have investigated whether intracerebral inoculation of brain and spinal cord from CWD-infected mule deer transmits prion infection to transgenic mice overexpressing human prion protein with methionine or valine at polymorphic residue 129. These transgenic mice have been utilized in extensive transmission studies of human and animal prion disease and are susceptible to BSE and vCJD prions, allowing comparison with CWD. Here, we show that these mice proved entirely resistant to infection with mule deer CWD prions arguing that the transmission barrier associated with this prion strain/host combination is greater than that observed with classical BSE prions. However, it is possible that CWD may be caused by multiple prion strains. Further studies will be required to evaluate the transmission properties of distinct cervid prion strains as they are characterized
Blood spots as an alternative to whole blood collection and the effect of a small monetary incentive to increase participation in genetic association studies
<p>Abstract</p> <p>Background</p> <p>Collection of buccal cells from saliva for DNA extraction offers a less invasive and convenient alternative to venipuncture blood collection that may increase participation in genetic epidemiologic studies. However, dried blood spot collection, which is also a convenient method, offers a means of collecting peripheral blood samples from which analytes in addition to DNA can be obtained.</p> <p>Methods</p> <p>To determine if offering blood spot collection would increase participation in genetic epidemiologic studies, we conducted a study of collecting dried blood spot cards by mail from a sample of female cancer cases (n = 134) and controls (n = 256) who were previously selected for a breast cancer genetics study and declined to provide a venipuncture blood sample. Participants were also randomized to receive either a 2.00 incentive vs. 26% for no incentive, p = 0.6), it was significantly associated with participation among the breast cancer cases (48% vs. 27%, respectively, p = 0.01). There did not appear to be any bias in response since no differences between cases and controls and incentive groups were observed when examining several demographic, work history and radiation exposure variables.</p> <p>Conclusion</p> <p>This study demonstrates that collection of dried blood spot cards in addition to venipuncture blood samples may be a feasible method to increase participation in genetic case-control studies.</p
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