17,035 research outputs found
Quantifying Tensions between CMB and Distance Datasets in Models with Free Curvature or Lensing Amplitude
Recent measurements of the Cosmic Microwave Background (CMB) by the Planck
Collaboration have produced arguably the most powerful observational evidence
in support of the standard model of cosmology, i.e. the spatially flat
CDM paradigm. In this work, we perform model selection tests to
examine whether the base CMB temperature and large scale polarization
anisotropy data from Planck 2015 (P15) prefer any of eight commonly used
one-parameter model extensions with respect to flat CDM. We find a
clear preference for models with free curvature, , or free
amplitude of the CMB lensing potential, . We also further develop
statistical tools to measure tension between datasets. We use a Gaussianization
scheme to compute tensions directly from the posterior samples using an
entropy-based method, the surprise, as well as a calibrated evidence ratio
presented here for the first time. We then proceed to investigate the
consistency between the base P15~CMB data and six other CMB and distance
datasets. In flat CDM we find a tension between the base
P15~CMB data and a distance ladder measurement, whereas the former are
consistent with the other datasets. In the curved CDM model we find
significant tensions in most of the cases, arising from the well-known low
power of the low- multipoles of the CMB data. In the flat CDM
model, however, all datasets are consistent with the base
P15~CMB observations except for the CMB lensing measurement, which remains in
significant tension. This tension is driven by the increased power of the CMB
lensing potential derived from the base P15~CMB constraints in both models,
pointing at either potentially unresolved systematic effects or the need for
new physics beyond the standard flat CDM model.Comment: 16 pages, 8 figures, 6 table
Curved Space or Curved Vacuum?
While the simple picture of a spatially flat, matter plus cosmological
constant universe fits current observation of the accelerated expansion, strong
consideration has also been given to models with dynamical vacuum energy. We
examine the tradeoff of ``curving'' the vacuum but retaining spatial flatness,
vs. curving space but retaining the cosmological constant. These different
breakdowns in the simple picture could readily be distinguished by combined
high accuracy supernovae and cosmic microwave background distance measurements.
If we allow the uneasy situation of both breakdowns, the curvature can still be
measured to 1%, but at the price of degrading estimation of the equation of
state time variation by 60% or more, unless additional information (such as
weak lensing data or a tight matter density prior) is included.Comment: 7 pages, 6 figures; minor changes to match version accepted to
Astroparticle Physics and correct typo at bottom of page
Regularization of spherical and axisymmetric evolution codes in numerical relativity
Several interesting astrophysical phenomena are symmetric with respect to the
rotation axis, like the head-on collision of compact bodies, the collapse
and/or accretion of fields with a large variety of geometries, or some forms of
gravitational waves. Most current numerical relativity codes, however, can not
take advantage of these symmetries due to the fact that singularities in the
adapted coordinates, either at the origin or at the axis of symmetry, rapidly
cause the simulation to crash. Because of this regularity problem it has become
common practice to use full-blown Cartesian three-dimensional codes to simulate
axi-symmetric systems. In this work we follow a recent idea idea of Rinne and
Stewart and present a simple procedure to regularize the equations both in
spherical and axi-symmetric spaces. We explicitly show the regularity of the
evolution equations, describe the corresponding numerical code, and present
several examples clearly showing the regularity of our evolutions.Comment: 11 pages, 9 figures. Several changes. Main corrections are in eqs.
(2.12) and (5.14). Accepted in Gen. Rel. Gra
Excision boundary conditions for black hole initial data
We define and extensively test a set of boundary conditions that can be
applied at black hole excision surfaces when the Hamiltonian and momentum
constraints of general relativity are solved within the conformal thin-sandwich
formalism. These boundary conditions have been designed to result in black
holes that are in quasiequilibrium and are completely general in the sense that
they can be applied with any conformal three-geometry and slicing condition.
Furthermore, we show that they retain precisely the freedom to specify an
arbitrary spin on each black hole. Interestingly, we have been unable to find a
boundary condition on the lapse that can be derived from a quasiequilibrium
condition. Rather, we find evidence that the lapse boundary condition is part
of the initial temporal gauge choice. To test these boundary conditions, we
have extensively explored the case of a single black hole and the case of a
binary system of equal-mass black holes, including the computation of
quasi-circular orbits and the determination of the inner-most stable circular
orbit. Our tests show that the boundary conditions work well.Comment: 23 pages, 23 figures, revtex4, corrected typos, added reference,
minor content changes including additional post-Newtonian comparison. Version
accepted by PR
Testing flatness of the universe with probes of cosmic distances and growth
When using distance measurements to probe spatial curvature, the geometric
degeneracy between curvature and dark energy in the distance-redshift relation
typically requires either making strong assumptions about the dark energy
evolution or sacrificing precision in a more model-independent approach.
Measurements of the redshift evolution of the linear growth of perturbations
can break the geometric degeneracy, providing curvature constraints that are
both precise and model-independent. Future supernova, CMB, and cluster data
have the potential to measure the curvature with an accuracy of
sigma(Omega_K)=0.002, without specifying a particular dark energy
phenomenology. In combination with distance measurements, the evolution of the
growth function at low redshifts provides the strongest curvature constraint if
the high-redshift universe is well approximated as being purely matter
dominated. However, in the presence of early dark energy or massive neutrinos,
the precision in curvature is reduced due to additional degeneracies, and
precise normalization of the growth function relative to recombination is
important for obtaining accurate constraints. Curvature limits from distances
and growth compare favorably to other approaches to curvature estimation
proposed in the literature, providing either greater accuracy or greater
freedom from dark energy modeling assumptions, and are complementary due to the
use of independent data sets. Model-independent estimates of curvature are
critical for both testing inflation and obtaining unbiased constraints on dark
energy parameters.Comment: 23 pages, 11 figures; submitted to Phys. Rev.
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