413 research outputs found
The effect of reionization on the CMB-density correlation
In this paper we show how the rescattering of CMB photons after cosmic
reionization can give a significant linear contribution to the
temperature-matter cross-correlation measurements. These anisotropies, which
arise via a late time Doppler effect, are on scales much larger than the
typical scale of non-linear effects at reionization; they can contribute to
degree scale cross-correlations and could affect the interpretation of similar
correlations resulting from the integrated Sachs-Wolfe effect. While expected
to be small at low redshifts, these correlations can be large given a probe of
the density at high redshift, and so could be a useful probe of the cosmic
reionization history.Comment: 8 pages, 8 figure
An indirect limit on the amplitude of primordial Gravitational Wave Background from CMB-Galaxy Cross Correlation
While large scale cosmic microwave background (CMB) anisotropies involve a
combination of the scalar and tensor fluctuations, the scalar amplitude can be
independently determined through the CMB-galaxy cross-correlation. Using
recently measured cross-correlation amplitudes, arising from the
cross-correlation between galaxies and the Integrated Sachs Wolfe effect in CMB
anisotropies, we obtain a constraint r < 0.5 at 68% confidence level on the
tensor-to-scalar fluctuation amplitude ratio. The data also allow us to exclude
gravity waves at a level of a few percent, relative to the density field, in a
low - Lambda dominated universe(Omega_Lambda~0.5). In future, joining
cross-correlation ISW measurements, which captures cosmological parameter
information, with independent determinations of the matter density and CMB
anisotropy power spectrum, may constrain the tensor-to-scalar ratio to a level
above 0.05. This value is the ultimate limit on tensor-to-scalar ratio from
temperature anisotropy maps when all other cosmological parameters except for
the tensor amplitude are known and the combination with CMB-galaxy correlation
allows this limit to be reached easily by accounting for degeneracies in
certain cosmological parameters.Comment: 5 Pages, 1 Figure, revised discussion on cosmic variance limits on
the tensor-to-scalar ratio from CMB, matches PRD accepted versio
Effects of standard and modified gravity on interplanetary ranges
We numerically investigate the impact on the two-body range by several
Newtonian and non-Newtonian dynamical effects for some Earth-planet (Mercury,
Venus, Mars, Jupiter, Saturn) pairs in view of the expected cm-level accuracy
in some future planned or proposed interplanetary ranging operations
(abridged).Comment: LaTex, World Scientific style, 46 pages, 55 figures, 1 table, 57
references. Version in press in International Journal of Modern Physics D
(IJMPD
Cosmological and Solar-System Tests of f(R) Modified Gravity
We investigate the cosmological and the local tests of the f(R) theory of
modified gravity via the observations of (1) the cosmic expansion and (2) the
cosmic structures and via (3) the solar-system experiments. To fit the possible
cosmic expansion histories under consideration, for each of them we reconstruct
f(R), known as "designer f(R)". We then test the designer f(R) via the
cosmic-structure constraints on the metric perturbation ratio Psi/Phi and the
effective gravitational coupling G_eff and via the solar-system constraints on
the Brans-Dicke theory with the chameleon mechanism. We find that among the
designer f(R) models specified by the CPL effective equation of state w_eff,
only the model closely mimicking general relativity with a cosmological
constant (LambdaCDM) can survive all the tests. Accordingly, these tests rule
out the frequently studied "w_eff = -1" designer f(R) models which are distinct
in cosmic structures from LambdaCDM. When considering only the cosmological
tests, we find that the surviving designer f(R) models, although exist for a
variety of w_eff, entail fine-tuning.Comment: 22 pages, 9 figures, LaTe
Dark energy survey year 3 results: High-precision measurement and modeling of galaxy-galaxy lensing
We present and characterize the galaxy-galaxy lensing signal measured using the first three years of data from the Dark Energy Survey (DES Y3) covering 4132 deg2. These galaxy-galaxy measurements are used in the DES Y3 3 × 2 pt cosmological analysis, which combines weak lensing and galaxy clustering information. We use two lens samples: a magnitude-limited sample and the redmagic sample, which span the redshift range ∼0.2-1 with 10.7 and 2.6 M galaxies, respectively. For the source catalog, we use the metacalibration shape sample, consisting of ≃100 M galaxies separated into four tomographic bins. Our galaxy-galaxy lensing estimator is the mean tangential shear, for which we obtain a total SNR of ∼148 for maglim (∼120 for redmagic), and ∼67 (∼55) after applying the scale cuts of 6 Mpc/h. Thus we reach percent-level statistical precision, which requires that our modeling and systematic-error control be of comparable accuracy. The tangential shear model used in the 3 × 2 pt cosmological analysis includes lens magnification, a five-parameter intrinsic alignment model, marginalization over a point mass to remove information from small scales and a linear galaxy bias model validated with higher-order terms. We explore the impact of these choices on the tangential shear observable and study the significance of effects not included in our model, such as reduced shear, source magnification, and source clustering. We also test the robustness of our measurements to various observational and systematics effects, such as the impact of observing conditions, lens-source clustering, random-point subtraction, scale-dependent metacalibration responses, point spread function residuals, and B mode
ISW effect in Unified Dark Matter Scalar Field Cosmologies: an analytical approach
We perform an analytical study of the Integrated Sachs-Wolfe (ISW) effect
within the framework of Unified Dark Matter models based on a scalar field
which aim at a unified description of dark energy and dark matter. Computing
the temperature power spectrum of the Cosmic Microwave Background anisotropies
we are able to isolate those contributions that can potentially lead to strong
deviations from the usual ISW effect occurring in a CDM universe. This
helps to highlight the crucial role played by the sound speed in the Unified
Dark Matter models. Our treatment is completely general in that all the results
depend only on the speed of sound of the dark component and thus it can be
applied to a variety of unified models, including those which are not described
by a scalar field but relies on a single dark fluid.Comment: 15 pages, LateX file; one comment after Eq.(36) and formula (44)
added in order to underline procedure and main results. Accepted for
publication in JCAP; some typos correcte
Constraints on Gauss-Bonnet Gravity in Dark Energy Cosmologies
Models with a scalar field coupled to the Gauss-Bonnet Lagrangian appear
naturally from Kaluza-Klein compactifications of pure higher-dimensional
gravity. We study linear, cosmological perturbations in the limits of weak
coupling and slow-roll, and derive simple expressions for the main observable
sub-horizon quantities: the anisotropic stress factor, the time-dependent
gravitational constant, and the matter perturbation growth factor. Using
present observational data, and assuming slow-roll for the dark energy field,
we find that the fraction of energy density associated with the coupled
Gauss-Bonnet term cannot exceed 15%. The bound should be treated with caution,
as there are significant uncertainies in the data used to obtain it. Even so,
it indicates that the future prospects for constraining the coupled
Gauss-Bonnet term with cosmological observations are encouraging.Comment: 15 pages. v3: extended analysis, conclusions change
Constraints on scalar-tensor theories of gravity from observations
In spite of their original discrepancy, both dark energy and modified theory
of gravity can be parameterized by the effective equation of state (EOS)
for the expansion history of the Universe. A useful model independent
approach to the EOS of them can be given by so-called
Chevallier-Polarski-Linder (CPL) parametrization where two parameters of it
( and ) can be constrained by the geometrical
observations which suffer from degeneracies between models. The linear growth
of large scale structure is usually used to remove these degeneracies. This
growth can be described by the growth index parameter and it can be
parameterized by in general. We use the
scalar-tensor theories of gravity (STG) and show that the discernment between
models is possible only when is not negligible. We show that the
linear density perturbation of the matter component as a function of redshift
severely constrains the viable subclasses of STG in terms of and
. From this method, we can rule out or prove the viable STG in future
observations. When we use , shows the convex shape of evolution
in a viable STG model. The viable STG models with are not
distinguishable from dark energy models when we strongly limit the solar system
constraint.Comment: 19 pages, 20 figures, 2 tables, submitted to JCA
Constraints on AGN feedback from its Sunyaev-Zel'dovich imprint on the cosmic background radiation
We derive constraints on feedback by active galactic nuclei (AGN) by setting limits on their thermal Sunyaev-Zel'dovich (SZ) imprint on the cosmic microwave background. The amplitude of any SZ signature is small and degenerate with the poorly known sub-mm spectral energy distribution of the AGN host galaxy and other unresolved dusty sources along the line of sight. Here we break this degeneracy by combining microwave and sub-mm data from with all-sky far-infrared maps from the AKARI satellite. We first test our measurement pipeline using the Sloan Digital Sky Survey (SDSS) redMaPPer catalogue of galaxy clusters, finding a highly significant detection (>20) of the SZ effect together with correlated dust emission. We then constrain the SZ signal associated with spectroscopically confirmed quasi-stellar objects (QSOs) from SDSS data release 7 (DR7) and the Baryon Oscillation Spectroscopic Survey (BOSS) DR12. We obtain a low-significance (1.6) hint of an SZ signal, pointing towards a mean thermal energy of 5 × 10 erg, lower than reported in some previous studies. A comparison of our results with high-resolution hydrodynamical simulations including AGN feedback suggests QSO host masses of ~ 4 × 10M, but with a large uncertainty. Our analysis provides no conclusive evidence for an SZ signal specifically associated with AGN feedback.BS acknowledges support from an Isaac Newton Studentship at the University of Cambridge and from the Science and Technology Facilities Council (STFC). TG acknowledges support from the Kavli Foundation and STFC grant ST/L000636/1. DS acknowledges support by the STFC and the ERC Starting Grant 638707 ‘Black holes and their host galaxies: coevolution across cosmic time’. This research is based on observations obtained with Planck (http://www.esa.int/Planck), an ESA science mission with instruments and contributions directly funded by ESA Member States, NASA and Canada. Furthermore, it is, in parts, based on observations with AKARI, a JAXA project with the participation of ESA. Funding for SDSS-III has been provided by the Alfred P. Sloan Foundation, the Participating Institutions, the National Science Foundation and the U.S. Department of Energy Office of Science. The SDSS-III web site is http://www.sdss3.org/. SDSS-III is managed by the Astrophysical Research Consortium for the Participating Institutions of the SDSS-III Collaboration
- …