39 research outputs found
Integrated Markov Chain Monte Carlo (MCMC) analysis of primordial non-Gaussianity (f_NL) in the recent CMB data
We have made a Markov Chain Monte Carlo (MCMC) analysis of primordial
non-Gaussianity (f_NL) using the WMAP bispectrum and power spectrum. In our
analysis, we have simultaneously constrained f_NL and cosmological parameters
so that the uncertainties of cosmological parameters can properly propagate to
the f_NL estimation. Investigating the parameter likelihoods deduced from MCMC
samples, we find slight deviation from Gaussian shape, which makes a Fisher
matrix estimation less accurate. Therefore, we have estimated the confidence
interval of f_NL by exploring the parameter likelihood without using the Fisher
matrix. We find that the best-fit values of our analysis make a good agreement
with other results, but the confidence interval is slightly different.Comment: v3: mean likelihoods added, v4: 2D likelihood added, typos corrected,
v5: the point sharpene
How to make a clean separation between CMB E and B modes with proper foreground masking
We investigate the E/B decomposition of CMB polarization on a masked sky. In
real space, operators of E and B mode decomposition involve only differentials
of CMB polarization. We may, therefore in principle, perform a clean E/B
decomposition from incomplete sky data. Since it is impractical to apply second
derivatives to observation data, we usually rely on spherical harmonic
transformation and inverse transformation, instead of using real-space
operators. In spherical harmonic representation, jump discontinuities in a cut
sky produces Gibbs phenomenon, unless a spherical harmonic expansion is made up
to an infinitely high multipole. By smoothing a foreground mask, we may
suppress the Gibbs phenomenon effectively in a similar manner to apodization of
a foreground mask discussed in other works. However, we incur foreground
contamination by smoothing a foreground mask, because zero-value pixels in the
original mask may be rendered non-zero by the smoothing process. In this work,
we investigate an optimal foreground mask, which ensures proper foreground
masking and suppresses Gibbs phenomenon. We apply our method to a simulated map
of the pixel resolution comparable to the Planck satellite. The simulation
shows that the leakage power is lower than unlensed CMB B mode power spectrum
of tensor-to-scalar ratio . We compare the result with
that of the original mask. We find that the leakage power is reduced by a
factor of at the cost of a sky fraction , and that
the enhancement is highest at lowest multipoles. We confirm that all the
zero-value pixels in the original mask remain zero in our mask. The application
of this method to the Planck data will improve the detectability of primordial
tensor perturbation.Comment: v2: typos corrected, v3: matched with the published version (the
clarity improved) v4: a typo corrected v5: a bibliography file error fixe
Optimizing interferometer experiments for CMB B mode measurement
The sensitivity of interferometers with linear polarizers to the CMB E and B
mode are variant under the rotation of the polarizer frame, while
interferometer with circular polarizers are equally sensitive to E and B mode.
We present analytically and numerically that the diagonal elements of window
functions for CMB E/B power spectra are maximized in interferometric
measurement of linear polarization, when the polarizer frame is in certain
rotation from the associated baseline. We also present the simulated
observation to show that the 1- errors on E/B mode power spectrum
estimation are variant under the polarizer frame rotation in the case of linear
polarizers, while they are invariant in the case of circular polarizers.
Simulation of the configuration similar to the DASI shows that minimum
1- error on B mode in interferometer measurement with linear polarizers
is 26% of that in interferometric measurement with circular polarizers. The
simulation also shows that the E/B mixing in interferometer measurement with
linear polarizers can be as low as 23% of that in interferometric measurement
with circular polarizers. It is not always possible to physically align the
polarizer frame with all the associated baselines in the case of an
interferometer array (N2). There exist certain linear combinations of
visibilities, which are equivalent to visibilities of the optimal polarizer
frame rotation. We present the linear combinations, which enables B mode
optimization for an interferometer array (N2).Comment: v2: file error corrected, v3: a footnote added, v4: a typo corrected
v10: some pdf file problem fixe
Lack of angular correlation and odd-parity preference in CMB data
We have investigated the angular correlation in the recent CMB data. In
addition to the known large-angle correlation anomaly, we find the lack of
correlation at small angles with high statistical significance. We have
investigated various non-cosmological contamination and additionally WMAP
team's simulated data. However, we have not found a definite cause. In the
angular power spectrum of WMAP data, there exist anomalous odd-parity
preference at low multipoles. Noting the equivalence between the power spectrum
and the correlation, we have investigated the association between the lack of
large-angle correlation and the odd-parity preference. From our investigation,
we find that the odd-parity preference at low multipoles is, in fact, a
phenomenological origin of the lack of large-angle correlation. Futher
investigation is required to find out whether the origin of the anomaly is
cosmological or due to unaccounted systematics. The data from Planck surveyor,
which has systematics distinct from the WMAP, will greatly help us to resolve
its origin.Comment: v3: typos corrected, v4: plots updated, v5: analysis extended, v6:
matched with the accepted version in ApJ (minor change
Limits on anisotropic inflation from the Planck data
Temperature anisotropy of the cosmic microwave background offers a test of
the fundamental symmetry of spacetime during cosmic inflation. Violation of
rotational symmetry yields a distinct signature in the power spectrum of
primordial fluctuations as , where is a
preferred direction in space and is an amplitude. Using the
\textit{Planck} 2013 temperature maps, we find no evidence for violation of
rotational symmetry, (68% CL), once the known effects of
asymmetry of the \textit{Planck} beams and Galactic foreground emission are
removed.Comment: 5 pages, 2 figures. (v2) References added. A typo fixed. (v3) Various
confidence levels included, Journal reference added (v4) error of a
duplicated pdf file fixe
CMB data constraint on self-annihilation of dark matter particles
Recently, self-annihilation of dark matter particles is proposed to explain
the "WMAP Haze" and excess of energetic positrons and electrons in ATIC and
PAMELA results. If self-annihilation of dark matter occurs around the
recombination of cosmic plasma, energy release from self-annihilation of dark
matter delays the recombination, and hence affects CMB anisotropy. By using the
recent CMB data, we have investigated the self-annihilation of dark matter
particles. In this investigation, we do not find statistically significant
evidence, and impose an upper bound on / m_chi. The upcoming data
from Planck surveyor and the Fermi Gamma-ray telescope will allow us to break
some of parameter degeneracy and improve constraints on self-annihilation of
dark matter particles.Comment: a talk presented at the Invisible Universe International Conference
at the Palais de l'UNESCO, Paris, v2: references adde
Parametric tension between even and odd multipole data of WMAP power spectrum: unaccounted contamination or missing parameters?
There exist power contrast in even and odd multipoles of WMAP power spectrum
at low and intermediate multipole range. This anomaly is explicitly associated
with the angular power spectrum, which are heavily used for cosmological model
fitting. Having noted this, we have investigated whether even(odd) multipole
data set is consistent with the WMAP concordance model. Our investigation shows
WMAP concordance model does not make a good fit for even(odd) multipole data
set, and there exist tension between two data subsets. Noting tension is
highest in primordial power spectrum parameters, we have additionally
considered a running spectral index, but find tension increases to even a
higher level. We believe these parametric tensions may be indications of
unaccounted contamination or imperfection of the model.Comment: v2: Latex error fixed, v3: matched with the accepted version in ApJL,
conclusion unchange
Cosmological Alfv\'en waves in the recent CMB data, and the observational bound on the primordial vector perturbation
In the presence of the primordial magnetic field, initial vector (vorticity)
perturbations produce cosmological Alfven waves and leave imprints on cosmic
microwave background (CMB) temperature and polarization anisotropy. We have
investigated imprints of cosmological Alfven waves in CMB anisotropy. For data
constraints, we have used the power spectrum of the recent CMB observations,
and correlations estimated from WMAP Internal Linear Combination (ILC) maps.
Our analysis shows 3 sigma evidence of cosmological Alfven waves. Using the 3
sigma limit from our analysis and the Alfven velocity limit from the total
energy density constraint, we impose a lower bound on the amplitude of
primordial vector perturbation: 4*10^-12 at k_0=0.002/Mpc.Comment: v2: change in analysis method and confidence interval improved v3:
typos corrected v4: a typo in Eq. 36 corrected v5: lower bound on vector
perturbation in more compliant form for ease of comparison, references adde
Direct reconstruction of spherical harmonics from interferometer observations of the CMB polarization
Interferometric observation of the CMB polarization can be expressed as a
linear sum of spherical harmonic coefficients of the CMB
polarization. The linear weight for depends on the observational
configuration such as antenna pointing, baseline orientation, and spherical
harmonic number . Since an interferometer is sensitive over a finite range
of multipoles, in the range can be determined by fitting for visibilities of various observational configurations. The formalism
presented in this paper enables the determination of directly
from spherical harmonic spaces without spherical harmonic transformation of
pixellized maps. The result of its application to a simulated observation is
presented with the formalism.Comment: v2: references updated, v3: a typo corrected v9: a pdf file problem
fixe
Removing the ISW-lensing bias from the local-form primordial non-Gaussianity estimation
The Integrated Sachs-Wolfe (ISW) effect produces a secondary temperature
anisotropy of CMB. The main contribution comes from z<2, where dark energy
leads to a decay of potentials. As the same photons are gravitationally lensed
by these decaying potentials, there exists a high degree of correlation between
the ISW effect and CMB lensing, leading to a non-zero three-point correlation
(bispectrum) of the observed temperature anisotropy. This ISW-lensing
bispectrum, whose shape resembles that of the so-called "local-form" primordial
bispectrum parametrized by fNL, is known to be the largest contamination of
fNL. In order to avoid a spurious detection of primordial non-Gaussianity, we
need to remove the ISW-lensing bias. In this work, we investigate three
debiasing methods: (I) subtraction of an expected, ensemble average of the
ISW-lensing bispectrum; (II) subtraction of a measured ISW-lensing bispectrum;
and (III) direct subtraction of an estimated ISW signal from an observed
temperature map. One may use an estimation of the ISW map from external non-CMB
data or that from the CMB data themselves. As the methods II and III are based
on fewer assumptions about the nature of dark energy, they are preferred over
the method I. While the methods I and II yield unbiased estimates of fNL with
comparable error bars, the method III yields a biased result when the
underlying primordial fNL is non-zero and the ISW map is estimated from a
lensing potential reconstructed from the observed temperature map. One of the
sources of the bias is a lensing reconstruction noise bias which is independent
of fNL and can be calculated precisely, but other fNL-dependent terms are
difficult to compute reliably. We thus conclude that the method II is the best,
model-independent way to remove the ISW-lensing bias of fNL, enabling us to
test the physics of inflation with smaller systematic errors.Comment: 17 pages, comments are welcomed v2: references added, v3: references
adde