312 research outputs found
Crossing the Phantom Divide with Parameterized Post-Friedmann Dark Energy
Dark energy models with a single scalar field cannot cross the equation of
state divide set by a cosmological constant. More general models that allow
crossing require additional degrees of freedom to ensure gravitational
stability. We show that a parameterized post-Friedmann description of cosmic
acceleration provides a simple but accurate description of multiple scalar
field crossing models. Moreover the prescription provides a well controlled
approximation for a wide range of "smooth" dark energy models. It conserves
energy and momentum and is exact in the metric evolution on scales well above
and below the transition scale to relative smoothness. Standard linear
perturbation tools have been altered to include this description and made
publicly available for studies of the dark energy involving cosmological
structure out to the horizon scale.Comment: 4 pages, 2 figures, code available at http://camb.info/ppf, minor
revisions reflect PRD published versio
Constraining Dark Energy by Combining Cluster Counts and Shear-Shear Correlations in a Weak Lensing Survey
We study the potential of a large future weak-lensing survey to constrain
dark energy properties by using both the number counts of detected galaxy
clusters (sensitive primarily to density fluctuations on small scales) and
tomographic shear-shear correlations (restricted to large scales). We use the
Fisher matrix formalism, assume a flat universe and parameterize the equation
of state of dark energy by w(a)=w_0+w_a(1-a), to forecast the expected
statistical errors from either observable, and from their combination. We show
that the covariance between these two observables is small, and argue that
therefore they can be regarded as independent constraints. We find that when
the number counts and the shear-shear correlations (on angular scales l < 1000)
are combined, an LSST (Large Synoptic Survey Telescope)-like survey can yield
statistical errors on (Omega_DE, w_0, w_a) as tight as (0.003, 0.03, 0.1).
These values are a factor of 2-25 better than using either observable alone.
The results are also about a factor of two better than those from combining
number counts of galaxy clusters and their power spectrum.Comment: 17 pages, 5 figures, 10 tables, submitted to PR
Cosmological Constraints on DGP Braneworld Gravity with Brane Tension
We perform a Markov Chain Monte Carlo analysis of the self-accelerating and
normal branch of Dvali-Gabadadze-Porrati braneworld gravity. By adopting a
parameterized post-Friedmann description of gravity, we utilize all of the
cosmic microwave background data, including the largest scales, and its
correlation with galaxies in addition to the geometrical constraints from
supernovae distances and the Hubble constant. We find that on both branches
brane tension or a cosmological constant is required at high significance with
no evidence for the unique Dvali-Gabadadze-Porrati modifications. The
cross-over scale must therefore be substantially greater than the Hubble scale
H_0 r_c > 3 and 3.5 at the 95% CL with and without uncertainties from spatial
curvature. With spatial curvature, the limit from the normal branch is
substantially assisted by the galaxy cross-correlation which highlights its
importance in constraining infrared modifications to gravity.Comment: 11 pages, 5 figures, 9 tables; replaced Hubble constant from HST Key
Project with measurement from SHOE
Challenges to the DGP Model from Horizon-Scale Growth and Geometry
We conduct a Markov Chain Monte Carlo study of the Dvali-Gabadadze-Porrati
(DGP) self-accelerating braneworld scenario given the cosmic microwave
background (CMB) anisotropy, supernovae and Hubble constant data by
implementing an effective dark energy prescription for modified gravity into a
standard Einstein-Boltzmann code. We find no way to alleviate the tension
between distance measures and horizon scale growth in this model. Growth
alterations due to perturbations propagating into the bulk appear as excess CMB
anisotropy at the lowest multipoles. In a flat cosmology, the maximum
likelihood DGP model is nominally a 5.3 sigma poorer fit than Lambda CDM.
Curvature can reduce the tension between distance measures but only at the
expense of exacerbating the problem with growth leading to a 4.8 sigma result
that is dominated by the low multipole CMB temperature spectrum. While changing
the initial conditions to reduce large scale power can flatten the temperature
spectrum, this also suppresses the large angle polarization spectrum in
violation of recent results from WMAP5. The failure of this model highlights
the power of combining growth and distance measures in cosmology as a test of
gravity on the largest scales.Comment: 12 pages, 7 figures, 4 tables, minor revisions reflect PRD published
versio
Probing massive neutrinos with the Minkowski functionals of the galaxy distribution
The characteristic signatures of massive neutrinos on large-scale structure
(LSS), if fully captured, can be used to put a stringent constraint on their
mass sum, . Previous work utilizing N-body simulations has shown the
Minkowski functionals (MFs) of LSS can reveal the imprints of massive neutrinos
on LSS, provide important complementary information to two-point statistics and
significantly improve constraints on . In this work, we take a step
forward and apply the statistics to the biased tracers of LSS, i.e. the
galaxies, and in redshift space. We perform a Fisher matrix analysis and
quantify the constraining power of the MFs by using the Molino mock galaxy
catalogs, which are constructed based on the halo occupation distribution (HOD)
framework with parameters for the SDSS and -22 galaxy samples. We
find the MFs give tighter constraints on all of the cosmological parameters
that we consider than the power spectrum. The constraints on
, and from
the MFs are better by a factor of 1.9, 2.9, 3.7, 4.2, 2.5, and 5.7,
respectively, after marginalizing over the HOD parameters. Specifically, for
, we obtain a 1 constraint of 0.059 eV with the MFs alone for
a volume of only .Comment: 33 pages, 5 + 4 figures, 4 tables. To be submitted to JCAP. Comments
welcome. arXiv admin note: text overlap with arXiv:2204.0294
Probing massive neutrinos with the Minkowski functionals of large-scale structure
Massive neutrinos suppress the growth of structure under their free-streaming
scales. The effect is most prominent on small scales where the widely-used
two-point statistics can no longer capture the full information. In this work,
we study the signatures massive neutrinos leave on large-scale structure (LSS)
as revealed by its morphological properties, which are fully described by
Minkowski functionals (MFs), and quantify the constraints on the summed
neutrino mass from the MFs, by using publicly available N-body
simulations. We find the MFs provide important complementary information, and
give tighter constraints on than the power spectrum. Specifically,
depending on whether massive neutrinos are included in the density field (the
`m' field) or not (the `cb' field), we find the constraint on from
the MFs with a smoothing scale of Mpc is or times better
than that from the power spectrum. When the MFs are combined with the power
spectrum, they can improve the constraint on from the latter by a
factor of 63 for the `m' field and 5 for the `cb' field. Notably, when the `m'
field is used, the constraint on from the MFs can reach eV
with a volume of , while the combination of the MFs and
power spectrum can tighten this constraint to be eV, a
significance on detecting the minimum sum of the neutrino masses. For the `m'
field, we also find the and degeneracy is broken with the
MFs, leading to stronger constraints on all 6 cosmological parameters
considered in this work than the power spectrum.Comment: Accepted for publication in JCAP. Changes from the first version: add
figure 10, and minor text revisions. Matches accepted version. 33 pages, 10
figures, 2 table
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