34 research outputs found
A measure of the impact of future dark energy experiments based on discriminating power among quintessence models
We evaluate the ability of future data sets to discriminate among different
quintessence dark energy models. This approach gives an alternative measure for
assessing the impact of future experiments, as compared with the large body of
literature that compares experiments in abstract parameter spaces and more
recent work that evaluates the constraining power of experiments on individual
parameter spaces of specific quintessence models. We use the Dark Energy Task
Force (DETF) models of future data sets, and compare the discriminative power
of experiments designated by the DETF as Stages 2, 3, and 4. Our work reveals a
minimal increase in discriminating power when comparing Stage 3 to Stage 2, but
a very striking increase in discriminating power when going to Stage 4. We also
see evidence that even modest improvements over DETF Stage 4 could result in
even more dramatic discriminating power among quintessence dark energy models.
We develop and demonstrate the technique of using the independently measured
modes of the equation of state as a common parameter space in which to compare
the different quintessence models, and we argue that this technique is a
powerful one. We use the PNGB, Exponential, Albrecht-Skordis, and Inverse
Tracker (or Inverse Power Law) quintessence models for this work. One of our
main results is that the goal of discriminating among these models sets a
concrete measure on the capabilities of future dark energy experiments.
Experiments have to be somewhat better than DETF Stage 4 simulated experiments
to fully meet this goal.Comment: 11 pages,10 figures, 4 labels V2: Figure resolution improved, typos
corrected V3: conclusions supplemented, submitted to PRD V4: Technical error
corrected (see footnote 26). No change to our main points and conclusion
Galaxy UV-luminosity function and reionization constraints on axion dark matter
If the dark matter (DM) were composed of axions, then structure formation in
the Universe would be suppressed below the axion Jeans scale. Using an analytic
model for the halo mass function of a mixed DM model with axions and cold dark
matter, combined with the abundance-matching technique, we construct the
UV-luminosity function. Axions suppress high- galaxy formation and the
UV-luminosity function is truncated at a faintest limiting magnitude. From the
UV-luminosity function, we predict the reionization history of the universe and
find that axion DM causes reionization to occur at lower redshift. We search
for evidence of axions using the Hubble Ultra Deep Field UV-luminosity function
in the redshift range -, and the optical depth to reionization,
, as measured from cosmic microwave background polarization. All probes
we consider consistently exclude from
contributing more than half of the DM, with our strongest constraint ruling
this model out at more than significance. In conservative models of
reionization a dominant component of DM with is in
tension with the measured value of , putting pressure on an
axion solution to the cusp-core problem. Tension is reduced to for
the axion contributing only half of the DM. A future measurement of the
UV-luminosity function in the range - by JWST would provide further
evidence for or against . Probing still higher masses
of will be possible using future measurements of the
kinetic Sunyaev-Zel'dovich effect by Advanced ACTPol to constrain the time and
duration of reionization.Comment: 17 pages, 8 figures, 2 tables. v2: Minor Changes. References added.
Published in MNRA
Curvature Constraints from the Causal Entropic Principle
Current cosmological observations indicate a preference for a cosmological
constant that is drastically smaller than what can be explained by conventional
particle physics. The Causal Entropic Principle (Bousso, {\it et al}.) provides
an alternative approach to anthropic attempts to predict our observed value of
the cosmological constant by calculating the entropy created within a causal
diamond. We have extended this work to use the Causal Entropic Principle to
predict the preferred curvature within the "multiverse". We have found that
values larger than are disfavored by more than 99.99% and a
peak value at and
for open universes. For universes that allow only positive curvature or both
positive and negative curvature, we find a correlation between curvature and
dark energy that leads to an extended region of preferred values. Our universe
is found to be disfavored to an extent depending the priors on curvature. We
also provide a comparison to previous anthropic constraints on open universes
and discuss future directions for this work.Comment: 5 pages, 3 Figure
Exploring Parameter Constraints on Quintessential Dark Energy: the Albrecht-Skordis model
We consider the effect of future dark energy experiments on
``Albrecht-Skordis'' (AS) models of scalar field dark energy using the
Monte-Carlo Markov chain method. We deal with the issues of parameterization of
these models, and have included spatial curvature as a parameter, finding it to
be important. We use the Dark Energy Task Force (DETF) simulated data to
represent future experiments and report our results in the form of likelihood
contours in the chosen parameter space. Simulated data is produced for cases
where the background cosmology has a cosmological constant, as well as cases
where the dark energy is provided by the AS model. The latter helps us
demonstrate the power of DETF Stage 4 data in the context of this specific
model. Though the AS model can produce equations of state functions very
different from what is possible with the parametrization used by the
DETF, our results are consistent with those reported by the DETF.Comment: 7 pages, including 9 figure
The Dark Matter Contribution to Galactic Diffuse Gamma Ray Emission
Observations of diffuse Galactic gamma ray emission (DGE) by the Fermi Large
Area Telescope (LAT) allow a detailed study of cosmic rays and the interstellar
medium. However, diffuse emission models of the inner Galaxy underpredict the
Fermi-LAT data at energies above a few GeV and hint at possible
non-astrophysical sources including dark matter (DM) annihilations or decays.
We present a study of the possible emission components from DM using the
high-resolution Via Lactea II N-body simulation of a Milky Way-sized DM halo.
We generate full-sky maps of DM annihilation and decay signals that include
modeling of the adiabatic contraction of the host density profile, Sommerfeld
enhanced DM annihilations, -wave annihilations, and decaying DM. We compare
our results with the DGE models produced by the Fermi-LAT team over different
sky regions, including the Galactic center, high Galactic latitudes, and the
Galactic anti-center. This work provides possible templates to fit the
observational data that includes the contribution of the subhalo population to
DM gamma-ray emission, with the significance depending on the
annihilation/decay channels and the Galactic regions being considered.Comment: Published by PR
Exploring Parameter Constraints on Quintessential Dark Energy: The Exponential Model
We present an analysis of a scalar field model of dark energy with an
exponential potential using the Dark Energy Task Force (DETF) simulated data
models. Using Markov Chain Monte Carlo sampling techniques we examine the
ability of each simulated data set to constrain the parameter space of the
exponential potential for data sets based on a cosmological constant and a
specific exponential scalar field model. We compare our results with the
constraining power calculated by the DETF using their ``''
parametrization of the dark energy. We find that respective increases in
constraining power from one stage to the next produced by our analysis give
results consistent with DETF results. To further investigate the potential
impact of future experiments, we also generate simulated data for an
exponential model background cosmology which can not be distinguished from a
cosmological constant at DETF ``Stage 2'', and show that for this cosmology
good DETF Stage 4 data would exclude a cosmological constant by better than
3.Comment: 11 pages including 10 figure
Exploring Parameter Constraints on Quintessential Dark Energy: the Inverse Power Law Model
We report on the results of a Markov Chain Monte Carlo (MCMC) analysis of an
inverse power law (IPL) quintessence model using the Dark Energy Task Force
(DETF) simulated data sets as a representation of future dark energy
experiments. We generate simulated data sets for a Lambda-CDM background
cosmology as well as a case where the dark energy is provided by a specific IPL
fiducial model and present our results in the form of likelihood contours
generated by these two background cosmologies. We find that the relative
constraining power of the various DETF data sets on the IPL model parameters is
broadly equivalent to the DETF results for the w_{0}-w_{a} parameterization of
dark energy. Finally, we gauge the power of DETF "Stage 4" data by
demonstrating a specific IPL model which, if realized in the universe, would
allow Stage 4 data to exclude a cosmological constant at better than the
3-sigma level.Comment: 15 pages, including 13 figure
Resonant sterile neutrino dark matter in the local and high-z Universe
Sterile neutrinos comprise an entire class of dark matter models that, depending on their production mechanism, can be hot, warm, or cold dark matter (CDM). We simulate the Local Group and representative volumes of the Universe in a variety of sterile neutrino models, all of which are consistent with the possible existence of a radiative decay line at ā¼3.5 keV. We compare models of production via resonances in the presence of a lepton asymmetry (suggested by Shi & Fuller 1999) to āthermalā models. We find that properties in the highly non-linear regime ā e.g. counts of satellites and internal properties of haloes and subhaloes ā are insensitive to the precise fall-off in power with wavenumber, indicating that non-linear evolution essentially washes away differences in the initial (linear) matter power spectrum. In the quasi-linear regime at higher redshifts, however, quantitative differences in the 3D matter power spectra remain, raising the possibility that such models can be tested with future observations of the Lyman-Ī± forest. While many of the sterile neutrino models largely eliminate multiple small-scale issues within the CDM paradigm, we show that these models may be ruled out in the near future via discoveries of additional dwarf satellites in the Local Group
Properties of resonantly produced sterile neutrino dark matter subhaloes
The anomalous 3.55 keV X-ray line recently detected towards a number of massive dark matter objects may be interpreted as the radiative decays of 7.1 keV mass sterile neutrino dark matter. Depending on its parameters, the sterile neutrino can range from cold to warm dark matter with small-scale suppression that differs in form from commonly adopted thermal warm dark matter. Here, we numerically investigate the subhalo properties for 7.1 keV sterile neutrino dark matter produced via the resonant ShiāFuller mechanism. Using accurate matter power spectra, we run cosmological zoom-in simulations of a Milky Way-sized halo and explore the abundance of massive subhaloes, their radial distributions, and their internal structure. We also simulate the halo with thermal 2.0 keV warm dark matter for comparison and discuss quantitative differences. We find that the resonantly produced sterile neutrino model for the 3.55 keV line provides a good description of structures in the Local Group, including the number of satellite dwarf galaxies and their radial distribution, and largely mitigates the too-big-to-fail problem. Future searches for satellite galaxies by deep surveys, such as the Dark Energy Survey, Large Synoptic Survey Telescope, and Wide Field Infrared Survey Telescope, will be a strong direct test of warm dark matter scenarios