997 research outputs found
Measuring primordial non-gaussianity without cosmic variance
Non-gaussianity in the initial conditions of the universe is one of the most
powerful mechanisms to discriminate among the competing theories of the early
universe. Measurements using bispectrum of cosmic microwave background
anisotropies are limited by the cosmic variance, i.e. available number of
modes. Recent work has emphasized the possibility to probe non-gaussianity of
local type using the scale dependence of large scale bias from highly biased
tracers of large scale structure. However, this power spectrum method is also
limited by cosmic variance, finite number of structures on the largest scales,
and by the partial degeneracy with other cosmological parameters that can mimic
the same effect. Here we propose an alternative method that solves both of
these problems. It is based on the idea that on large scales halos are biased,
but not stochastic, tracers of dark matter: by correlating a highly biased
tracer of large scale structure against an unbiased tracer one eliminates the
cosmic variance error, which can lead to a high signal to noise even from the
structures comparable to the size of the survey. The square of error
improvement on non-gaussianity parameter f_nl relative to the power spectrum
method scales as Pn/2, where P and n is the power spectrum and the number
density of the biased tracer, respectively. For an ideal survey out to z=2 the
error reduction can be as large as a factor of seven, which should guarantee a
detection of non-gaussianity from an all sky survey of this type. The
improvements could be even larger if high density tracers that are sensitive to
non-gaussianity can be identified and measured over a large volume.Comment: 7 page
Polarization of the Microwave Background in Defect Models
We compute the polarization power spectra for global strings, monopoles,
textures and nontopological textures, and compare them to inflationary models.
We find that topological defect models predict a significant (1 microK)
contribution to magnetic type polarization on degree angular scales, which is
produced by the large vector component of the defect source. We also
investigate the effect of decoherence on polarization. It leads to a smoothing
of acoustic oscillations both in temperature and polarization power spectra and
strongly suppresses the cross-correlation between temperature and polarization
relative to inflationary models. Presence or absence of magnetic polarization
or cross-correlation would be a strong discriminator between the two theories
of structure formation and will be testable with the next generation of CMB
satellites.Comment: 4 pages, 3 figures, RevTeX fil
CMBFAST for spatially closed universes
We extend the cosmological linear perturbation theory code CMBFAST to closed
geometries. This completes the implementation of CMBFAST to all types of
geometries and allows the user to perform an unlimited search in the parameter
space of models. This will be specially useful for placing confidence limits on
cosmological parameters from existing and future data. We discuss some of the
technical issues regarding the implementation.Comment: 6 pages, 2 figures, new version of CMBFAST can be found
http://www.sns.ias.edu/~matiasz/CMBFAST/cmbfast.htm
Lensing effect on polarization in microwave background: extracting convergence power spectrum
Matter inhomogeneities along the line of sight deflect the cosmic microwave
background (CMB) photons originating at the last scattering surface at redshift
. These distortions modify the pattern of CMB polarization. We
identify specific combinations of Stokes and parameters that correspond
to spin 0, variables and can be used to reconstruct the projected matter
density. We compute the expected signal to noise as a function of detector
sensitivity and angular resolution. With Planck satellite the detection would
be at a few level. Several times better detector sensitivity would be
needed to measure the projected dark matter power spectrum over a wider range
of scales, which could provide an independent confirmation of the projected
matter power spectrum as measured from other methods.Comment: 17 pages, 5 figures, accepted for publication in PR
Probing for Dynamics of Dark-Energy in Mass Varying Neutrinos: Cosmic Microwave Background Radiation and Large Scale Structure
We present cosmological perturbation theory in neutrino probe interacting
dark-energy models, and calculate cosmic microwave background anisotropies and
matter power spectrum. In these models, the evolution of the mass of neutrinos
is determined by the quintessence scalar field, which is responsible for the
cosmic acceleration today. We consider several types of scalar field potentials
and put constraints on the coupling parameter between neutrinos and dark
energy. Assuming the flatness of the universe, the constraint we can derive
from the current observation is at the 95 % confidence
level for the sum over three species of neutrinos.Comment: 12 pages, 8 figures, Present in conferences COSPA-2006, NEPSE-2007
and Yong-Pyung APCTP-200
Gravitational lensing as a contaminant of the gravity wave signal in CMB
Gravity waves (GW) in the early universe generate B-type polarization in the
cosmic microwave background (CMB), which can be used as a direct way to measure
the energy scale of inflation. Gravitational lensing contaminates the GW signal
by converting the dominant E polarization into B polarization. By
reconstructing the lensing potential from CMB itself one can decontaminate the
B mode induced by lensing. We present results of numerical simulations of B
mode delensing using quadratic and iterative maximum-likelihood lensing
reconstruction methods as a function of detector noise and beam. In our
simulations we find the quadratic method can reduce the lensing B noise power
by up to a factor of 7, close to the no noise limit. In contrast, the iterative
method shows significant improvements even at the lowest noise levels we
tested. We demonstrate explicitly that with this method at least a factor of 40
noise power reduction in lensing induced B power is possible, suggesting that
T/S=10^-6 may be achievable in the absence of sky cuts, foregrounds, and
instrumental systematics. While we do not find any fundamental lower limit due
to lensing, we find that for high-sensitivity detectors residual lensing noise
dominates over the detector noise.Comment: 6 pages, 2 figures, submitted to PR
Early reionization by decaying particles and cosmic microwave background radiation
We study the reionization scenario in which ionizing UV photons emitted from
decaying particle, in addition to usual contributions from stars and quasars,
ionize the universe. It is found that the scenario is consistent with both the
first year data of the Wilkinson Microwave Anisotropy Probe and the fact that
the universe is not fully ionized until z \sim 6 as observed by Sloan Digital
Sky Survey. Likelihood analysis revealed that rather broad parameter space can
be chosen. This scenario will be discriminated by future observations,
especially by the EE polarization power spectrum of cosmic microwave background
radiation.Comment: 5 pages, 5 figures, fig 2, table 1, and some typos are correcte
Testing Multi-Field Inflation with Galaxy Bias
Multi-field models of inflation predict an inequality between the amplitude
tauNL of the collapsed limit of the four-point correlator of the primordial
curvature perturbation and the amplitude fNL of the squeezed limit of its
three-point correlator. While a convincing detection of non-Gaussianity through
the squeezed limit of the three-point correlator would rule out all
single-field models, a robust confirmation or disproval of the inequality
between tauNL and fNL would provide crucial information about the validity of
multi-field models of inflation. In this paper, we discuss to which extent
future measurements of the scale-dependence of galaxy bias can test multi-field
inflationary scenarios. The strong degeneracy between the effect of a
non-vanishing fNL and tauNL on halo bias can be broken by considering multiple
tracer populations of the same surveyed volume. If halos down to 1e13 Msun/h
are resolved in a survey of volume 25(Gpc/h)^3, then testing multi-field models
of inflation at the 3-\sigma level would require, for instance, a detection of
tauNL at the level of tauNL~1e5 given a measurement of a local bispectrum with
amplitude fNL~10. However, we find that disproving multi-field models of
inflation with measurements of the non-Gaussian bias only will be very
challenging, unless |fNL| > 80 and one can achieve a halo mass resolution of
1e10 Msun/h.Comment: 8 pages, 4 figure
Power Spectra in Global Defect Theories of Cosmic Structure Formation
An efficient technique for computing perturbation power spectra in field
ordering theories of cosmic structure formation is introduced, enabling
computations to be carried out with unprecedented precision. Large scale
simulations are used to measure unequal time correlators of the source stress
energy, taking advantage of scaling during matter and radiation domination, and
causality, to make optimal use of the available dynamic range. The correlators
are then re-expressed in terms of a sum of eigenvector products, a
representation which we argue is optimal, enabling the computation of the final
power spectra to be performed at high accuracy. Microwave anisotropy and matter
perturbation power spectra for global strings, monopoles, textures and
non-topological textures are presented and compared with recent observations.Comment: 4 pages, compressed and uuencoded RevTex file and postscript figure
Constraints on non-thermal Dark Matter from Planck lensing extraction
Distortions of CMB temperature and polarization anisotropy maps caused by
gravitational lensing, observable with high angular resolution and sensitivity,
can be used to constrain the sterile neutrino mass, offering several advantages
against the analysis based on the combination of CMB, LSS and Ly\alpha forest
power spectra. As the gravitational lensing effect depends on the matter
distribution, no assumption on light-to-mass bias is required. In addition,
unlike the galaxy clustering and Ly\alpha forest power spectra, the projected
gravitational potential power spectrum probes a larger range of angular scales,
the non-linear corrections being required only at very small scales. Taking
into account the changes in the time-temperature relation of the primordial
plasma and the modification of the neutrino thermal potential, we compute the
projected gravitational potential power spectrum and its correlation with the
temperature in the presence of DM sterile neutrino. We show that the
cosmological parameters are generally not biased when DM sterile neutrino is
included. From this analysis we found a lower limit on DM sterile neutrino mass
m_s >2.08 keV at 95% CL, consistent with the lower mass limit obtained from the
combined analysis of CMB, SDSS 3D power spectrum and SDSS Ly\alpha forest power
spectrum ( keV). We conclude that although the information that
can be obtained from lensing extraction is rather limited due to the high level
of the lensing noise of Planck experiment, weak lensing of CMB offers a
valuable alternative to constrain the dark matter sterile neutrino mass.Comment: 15 pages, 6 figure
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