5,771 research outputs found
Exploring the Expansion History of the Universe
Exploring the recent expansion history of the universe promises insights into
the cosmological model, the nature of dark energy, and potentially clues to
high energy physics theories and gravitation. We examine the extent to which
precision distance-redshift observations can map out the history, including the
acceleration-deceleration transition, and the components and equations of state
of the energy density. We consider the ability to distinguish between various
dynamical scalar field models for the dark energy, as well as higher dimension
and alternate gravity theories. Finally, we present a new, advantageous
parametrization for the study of dark energy.Comment: 4 pages, 3 figures, submitted to Phys. Rev. Letter
Majorana fermions manifested as interface-states in semiconductor hybrid structures
Motivated by recent proposals for the generation of Majorana fermions in
semiconducting hybrid structures, we examine possible experimental fingerprints
of such excitations. Whereas previous works mainly have focused on zero-energy
states in vortex cores in this context, we demonstrate analytically an
alternative route to detection of Majorana excitations in semiconducting hybrid
structures: interface-bound states that may be probed directly via conductance
spectroscopy or STM-measurements. We estimate the necessary experimental
parameters required for observation of our predictions.Comment: 4 pages, 2 figures
The Paths of Quintessence
The structure of the dark energy equation of state phase plane holds
important information on the nature of the physics. We explain the bounds of
the freezing and thawing models of scalar field dark energy in terms of the
tension between the steepness of the potential vs. the Hubble drag.
Additionally, we extend the phase plane structure to modified gravity theories,
examine trajectories of models with certain properties, and categorize regions
in terms of scalar field hierarchical parameters, showing that dark energy is
generically not a slow roll phenomenon.Comment: 12 pages, 7 figures; matches PRD versio
Cross-Correlating Cosmic Microwave Background Radiation Fluctuations with Redshift Surveys: Detecting the Signature of Gravitational Lensing
Density inhomogeneities along the line-of-sight distort fluctuations in the
cosmic microwave background. Usually, this effect is thought of as a small
second-order effect that mildly alters the statistics of the microwave
background fluctuations. We show that there is a first-order effect that is
potentially observable if we combine microwave background maps with large
redshift surveys. We introduce a new quantity that measures this lensing
effect, , where T is the microwave
background temperature and is the lensing due to matter in the
region probed by the redshift survey. We show that the expected signal is first
order in the gravitational lensing bending angle, , and find that it should be easily detectable, (S/N) 15-35, if
we combine the Microwave Anisotropy Probe satellite and Sloan Digital Sky
Survey data. Measurements of this cross-correlation will directly probe the
``bias'' factor, the relationship between fluctuations in mass and fluctuations
in galaxy counts.Comment: 13 pages, 4 postscript figures included; Uses aaspp4.sty (AASTeX
v4.0); Accepted for publication in Astrophysical Journal, Part
Strong Gravitational Lensing and Dark Energy Complementarity
In the search for the nature of dark energy most cosmological probes measure
simple functions of the expansion rate. While powerful, these all involve
roughly the same dependence on the dark energy equation of state parameters,
with anticorrelation between its present value w_0 and time variation w_a.
Quantities that have instead positive correlation and so a sensitivity
direction largely orthogonal to, e.g., distance probes offer the hope of
achieving tight constraints through complementarity. Such quantities are found
in strong gravitational lensing observations of image separations and time
delays. While degeneracy between cosmological parameters prevents full
complementarity, strong lensing measurements to 1% accuracy can improve
equation of state characterization by 15-50%. Next generation surveys should
provide data on roughly 10^5 lens systems, though systematic errors will remain
challenging.Comment: 7 pages, 5 figure
Parametric resonance for antineutrino conversions using LSND best-fit results with a 3+1 flavor scheme
An analytical solution to a parametric resonance effect for antineutrinos in
a 3+1 flavor (active+sterile) scheme using multiple non-adiabatic density
shifts is presented. We derive the conditions for a full flavor conversion for
antineutrino oscillations
under the assumption that LSND best-fits for the mixing
parameters are valid in a short-baseline accelerator experiment. We show that
the parametric resonance effect can be exploited to increase the effective
antineutrino oscillation length by a factor of 10-40, thus sustaining a high
oscillation probability for a much longer period of time than in the vacuum
scenario. We propose a realistic experimental setup that could probe for this
effect which leaves a signature in terms of a specific oscillation probability
profile. Moreover, since the parametric resonance effect is valid in any 2 or
1+1 flavor approximation, our results could be suggestive for future
short-baseline accelerator neutrino detection experiments.Comment: 6 pages, 4 figure
AN EVALUATION OF INTEGRATED PEST MANAGEMENT WITH HETEROGENEOUS PARTICIPATION
Principal component analysis in employed to develop indices that distinguish between participants and nonparticipants in Integrated Pest Management (IPM) programs. Results of incorporating these indices into yield, net return, and production cost functions for cotton producers indicate that both yield and costs increase as the degree of producer participation in IPM increases. Although these results are inconsistent with previous research, they are consistent with the theoretical relationship between IPM and conventional input usage.Crop Production/Industries,
Contiguous redshift parameterizations of the growth index
The growth rate of matter perturbations can be used to distinguish between
different gravity theories and to distinguish between dark energy and modified
gravity at cosmological scales as an explanation to the observed cosmic
acceleration. We suggest here parameterizations of the growth index as
functions of the redshift. The first one is given by that
interpolates between a low/intermediate redshift parameterization
and a high
redshift constant value. For example, our interpolated form
can be used when including the CMB to the rest of the data while
the form can be used otherwise. It is found that the
parameterizations proposed achieve a fit that is better than 0.004% for the
growth rate in a CDM model, better than 0.014% for
Quintessence-Cold-Dark-Matter (QCDM) models, and better than 0.04% for the flat
Dvali-Gabadadze-Porrati (DGP) model (with ) for the entire
redshift range up to . We find that the growth index parameters
take distinctive values for dark energy models and
modified gravity models, e.g. for the CDM model
and for the flat DGP model. This provides a means for future
observational data to distinguish between the models.Comment: 7 pages, 6 figures, matches PRD accepted versio
Tunneling conductance in - and d-wave superconductor-graphene junctions: Extended Blonder-Tinkham-Klapwijk formalism
We investigate the conductance spectra of a normal/superconductor graphene
junction using the extended Blonder-Tinkham-Klapwijk formalism, considering
pairing potentials that are both conventional (isotropic s-wave) and
unconventional (anisotropic d-wave). In particular, we study the full crossover
from normal to specular Andreev reflection without restricting ourselves to
special limits and approximations, thus expanding results obtained in previous
work. In addition, we investigate in detail how the conductance spectra are
affected if it is possible to induce an unconventional pairing symmetry in
graphene, for instance a d-wave order parameter. We also discuss the recently
reported conductance-oscillations that take place in normal/superconductor
graphene junctions, providing both analytical and numerical results.Comment: 14 pages, 16 figures. High-resolution figures available in the
published versio
Comparison of organoleptic acceptability of liquid and fresh diets
Organoleptic acceptability of liquid and fresh diets for space flight feedin
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