6 research outputs found
Spatial gradients in the cosmological constant
It is possible that there may be differences in the fundamental physical
parameters from one side of the observed universe to the other. I show that the
cosmological constant is likely to be the most sensitive of the physical
parameters to possible spatial variation, because a small variation in any of
the other parameters produces a huge variation of the cosmological constant. It
therefore provides a very powerful {\em indirect} evidence against spatial
gradients or temporal variation in the other fundamental physical parameters,
at least 40 orders of magnitude more powerful than direct experimental
constraints. Moreover, a gradient may potentially appear in theories where the
variability of the cosmological constant is connected to an anthropic selection
mechanism, invoked to explain the smallness of this parameter. In the Hubble
damping mechanism for anthropic selection, I calculate the possible gradient.
While this mechanism demonstrates the existence of this effect, it is too small
to be seen experimentally, except possibly if inflation happens around the
Planck scale.Comment: 12 page
A New Approach to Testing Dark Energy Models by Observations
We propose a new approach to the consistency test of dark energy models with
observations. To test a category of dark energy models, we suggest introducing
a characteristic Q(z) that in general varies with the redshift z but in those
models plays the role of a (constant) distinct parameter. Then, by
reconstructing dQ(z)/dz from observational data and comparing it with zero we
can assess the consistency between data and the models under consideration. For
a category of models that passes the test, we can further constrain the
distinct parameter of those models by reconstructing Q(z) from data. For
demonstration, in this paper we concentrate on quintessence. In particular we
examine the exponential potential and the power-law potential via a widely used
parametrization of the dark energy equation of state, w(z) = w_0 + w_a z/(1+z),
for data analysis. This method of the consistency test is particularly
efficient because for all models we invoke the constraint of only a single
parameter space that by choice can be easily accessed. The general principle of
our approach is not limited to dark energy. It may also be applied to the
testing of various cosmological models and even the models in other fields
beyond the scope of cosmology.Comment: 19 pages, 5 figure
Supernova / Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy
The Supernova / Acceleration Probe (SNAP) is a proposed space-based
experiment designed to study the dark energy and alternative explanations of
the acceleration of the Universe's expansion by performing a series of
complementary systematics-controlled measurements. We describe a
self-consistent reference mission design for building a Type Ia supernova
Hubble diagram and for performing a wide-area weak gravitational lensing study.
A 2-m wide-field telescope feeds a focal plane consisting of a 0.7
square-degree imager tiled with equal areas of optical CCDs and near infrared
sensors, and a high-efficiency low-resolution integral field spectrograph. The
SNAP mission will obtain high-signal-to-noise calibrated light-curves and
spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A
wide-field survey covering one thousand square degrees resolves ~100 galaxies
per square arcminute. If we assume we live in a cosmological-constant-dominated
Universe, the matter density, dark energy density, and flatness of space can
all be measured with SNAP supernova and weak-lensing measurements to a
systematics-limited accuracy of 1%. For a flat universe, the
density-to-pressure ratio of dark energy can be similarly measured to 5% for
the present value w0 and ~0.1 for the time variation w'. The large survey area,
depth, spatial resolution, time-sampling, and nine-band optical to NIR
photometry will support additional independent and/or complementary dark-energy
measurement approaches as well as a broad range of auxiliary science programs.
(Abridged)Comment: 40 pages, 18 figures, submitted to PASP, http://snap.lbl.go
Recommended from our members
An integral field spectrograph for SNAP supernova studies
A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Ia supernovae and to standardize the magnitude of each candidate by determining explosion parameters. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have very high efficiency and low spectral resolution (R {approx} 100), constant through the wavelength range (0.35-1.7{micro}m), adapted to the scientific goals of the mission
Recommended from our members
An integral field spectrograph for SNAP supernova studies
A well-adapted spectrograph concept has been developed for the SNAP (SuperNova/Acceleration Probe) experiment. The goal is to ensure proper identification of Type Ia supernovae and to standardize the magnitude of each candidate by determining explosion parameters. An instrument based on an integral field method with the powerful concept of imager slicing has been designed and is presented in this paper. The spectrograph concept is optimized to have very high efficiency and low spectral resolution (R {approx} 100), constant through the wavelength range (0.35-1.7{micro}m), adapted to the scientific goals of the mission
Recommended from our members
Supernova / Acceleration Probe: A Satellite Experiment to Study the Nature of the Dark Energy
The Supernova / Acceleration Probe (SNAP) is a proposed space-based
experiment designed to study the dark energy and alternative explanations of
the acceleration of the Universe's expansion by performing a series of
complementary systematics-controlled measurements. We describe a
self-consistent reference mission design for building a Type Ia supernova
Hubble diagram and for performing a wide-area weak gravitational lensing study.
A 2-m wide-field telescope feeds a focal plane consisting of a 0.7
square-degree imager tiled with equal areas of optical CCDs and near infrared
sensors, and a high-efficiency low-resolution integral field spectrograph. The
SNAP mission will obtain high-signal-to-noise calibrated light-curves and
spectra for several thousand supernovae at redshifts between z=0.1 and 1.7. A
wide-field survey covering one thousand square degrees resolves ~100 galaxies
per square arcminute. If we assume we live in a cosmological-constant-dominated
Universe, the matter density, dark energy density, and flatness of space can
all be measured with SNAP supernova and weak-lensing measurements to a
systematics-limited accuracy of 1%. For a flat universe, the
density-to-pressure ratio of dark energy can be similarly measured to 5% for
the present value w0 and ~0.1 for the time variation w'. The large survey area,
depth, spatial resolution, time-sampling, and nine-band optical to NIR
photometry will support additional independent and/or complementary dark-energy
measurement approaches as well as a broad range of auxiliary science programs.
(Abridged