7,967 research outputs found
Primordial Bispectrum Information from CMB Polarization
After the precise observations of the Cosmic Microwave Background (CMB)
anisotropy power spectrum, attention is now being focused on the higher order
statistics of the CMB anisotropies. Since linear evolution preserves the
statistical properties of the initial conditions, observed non-Gaussianity of
the CMB will mirror primordial non-Gaussianity. Single field slow-roll
inflation robustly predicts negligible non-Gaussianity so an indication of
non-Gaussianity will suggest alternative scenarios need to be considered. In
this paper we calculate the information on primordial non-Gaussianity encoded
in the polarization of the CMB. After deriving the optimal weights for a cubic
estimator we evaluate the Signal-to-Noise ratio of the estimator for WMAP,
Planck and an ideal cosmic variance limited experiment. We find that when the
experiment can observe CMB polarization with good sensitivity, the sensitivity
to primordial non-Gaussianity increases by roughly a factor of two. We also
test the weakly non-Gaussian assumption used to derive the optimal weight
factor by calculating the degradation factor produced by the gravitational
lensing induced connected four-point function. The physical scales in the
radiative transfer functions are largely irrelevant for the constraints on the
primordial non-Gaussianity. We show that the total (S/N)^2 is simply
proportional to the number of observed pixels on the sky.Comment: To be submitted to PRD, 25 pages, 6 figure
Estimation of Minkowski tensors from digital grey-scale images
It has been shown that local algorithms based on grey-scale images sometimes
lead to asymptotically unbiased estimators for surface area and integrated mean
curvature. This paper extends the results to estimators for Minkowski tensors.
In particular, asymptotically unbiased local algorithms for estimation of all
volume and surface tensors and certain mean curvature tensors are given. This
requires an extension of the known asymptotic formulas to estimators with
position dependent weights.Comment: 15 page
CMB lensing and primordial squeezed non-Gaussianity
Squeezed primordial non-Gaussianity can strongly constrain early-universe
physics, but it can only be observed on the CMB after it has been
gravitationally lensed. We give a new simple non-perturbative prescription for
accurately calculating the effect of lensing on any squeezed primordial
bispectrum shape, and test it with simulations. We give the generalization to
polarization bispectra, and discuss the effect of lensing on the trispectrum.
We explain why neglecting the lensing smoothing effect does not significantly
bias estimators of local primordial non-Gaussianity, even though the change in
shape can be >~10%. We also show how tau_NL trispectrum estimators can be well
approximated by much simpler CMB temperature modulation estimators, and hence
that there is potentially a ~10-30% bias due to very large-scale lensing modes,
depending on the range of modulation scales included. Including dipole sky
modulations can halve the tau_NL error bar if kinematic effects can be
subtracted using known properties of the CMB temperature dipole. Lensing
effects on the g_NL trispectrum are small compared to the error bar. In
appendices we give the general result for lensing of any primordial bispectrum,
and show how any full-sky squeezed bispectrum can be decomposed into orthogonal
modes of distinct angular dependence.Comment: 22 pages, 6 figures; minor edits to match published versio
Inflation in Entropic Cosmology: Primordial Perturbations and non-Gaussianities
We investigate thermal inflation in double-screen entropic cosmology. We find
that its realization is general, resulting from the system evolution from
non-equilibrium to equilibrium. Furthermore, going beyond the background
evolution, we study the primordial curvature perturbations arising from the
universe interior, as well as from the thermal fluctuations generated on the
holographic screens. We show that the power spectrum is nearly scale-invariant
with a red tilt, while the tensor-to-scalar ratio is in agreement with
observations. Finally, we examine the non-Gaussianities of primordial curvature
perturbations, and we find that a sizable value of the non-linearity parameter
is possible due to holographic statistics on the outer screen.Comment: 10 pages, 3 figures, references added, accepted by PL
Baryons still trace dark matter: probing CMB lensing maps for hidden isocurvature
Compensated isocurvature perturbations (CIPs) are primordial fluctuations
that balance baryon and dark-matter isocurvature to leave the total matter
density unperturbed. The effects of CIPs on the cosmic microwave background
(CMB) anisotropies are similar to those produced by weak lensing of the CMB:
smoothing of the power spectrum, and generation of non-Gaussian features.
Previous work considered the CIP effects on the CMB power-spectrum but
neglected to include the CIP effects on estimates of the lensing potential
power spectrum (though its contribution to the non-Gaussian, connected, part of
the CMB trispectrum). Here, the CIP contribution to the standard estimator for
the lensing potential power-spectrum is derived, and along with the CIP
contributions to the CMB power-spectrum, Planck data is used to place limits on
the root-mean-square CIP fluctuations on CMB scales, . The resulting constraint of using this new technique improves on past work by a factor of
. We find that for Planck data our constraints almost reach the
sensitivity of the optimal CIP estimator. The method presented here is
currently the most sensitive probe of the amplitude of a scale-invariant CIP
power spectrum placing an upper limit of at 95% CL. Future
measurements of the large-scale CMB lensing potential power spectrum could
probe CIP amplitudes as low as ().Comment: 24 pages, 9 figures; comments welcome; v2 references correcte
Compensated isocurvature perturbations in the curvaton model
Primordial fluctuations in the relative number densities of particles, or
isocurvature perturbations, are generally well constrained by cosmic microwave
background (CMB) data. A less probed mode is the compensated isocurvature
perturbation (CIP), a fluctuation in the relative number densities of cold dark
matter and baryons. In the curvaton model, a subdominant field during inflation
later sets the primordial curvature fluctuation . In some curvaton-decay
scenarios, the baryon and cold dark matter isocurvature fluctuations nearly
cancel, leaving a large CIP correlated with . This correlation can be
used to probe these CIPs more sensitively than the uncorrelated CIPs considered
in past work, essentially by measuring the squeezed bispectrum of the CMB for
triangles whose shortest side is limited by the sound horizon. Here, the
sensitivity of existing and future CMB experiments to correlated CIPs is
assessed, with an eye towards testing specific curvaton-decay scenarios. The
planned CMB Stage 4 experiment could detect the largest CIPs attainable in
curvaton scenarios with more than 3 significance. The significance
could improve if small-scale CMB polarization foregrounds can be effectively
subtracted. As a result, future CMB observations could discriminate between
some curvaton-decay scenarios in which baryon number and dark matter are
produced during different epochs relative to curvaton decay. Independent of the
specific motivation for the origin of a correlated CIP perturbation,
cross-correlation of CIP reconstructions with the primary CMB can improve the
signal-to-noise ratio of a CIP detection. For fully correlated CIPs the
improvement is a factor of 23.Comment: 20 pages, 8 figures, minor changes matching publicatio
Primordial Non-Gaussianity in the Cosmic Microwave Background
In the last few decades, advances in observational cosmology have given us a
standard model of cosmology. We know the content of the universe to within a
few percent. With more ambitious experiments on the way, we hope to move beyond
the knowledge of what the universe is made of, to why the universe is the way
it is. In this review paper we focus on primordial non-Gaussianity as a probe
of the physics of the dynamics of the universe at the very earliest moments. We
discuss 1) theoretical predictions from inflationary models and their
observational consequences in the cosmic microwave background (CMB)
anisotropies; 2) CMB--based estimators for constraining primordial
non-Gaussianity with an emphasis on bispectrum templates; 3) current
constraints on non-Gaussianity and what we can hope to achieve in the near
future; and 4) non-primordial sources of non-Gaussianities in the CMB such as
bispectrum due to second order effects, three way cross-correlation between
primary-lensing-secondary CMB, and possible instrumental effects.Comment: 27 pages, 8 figures; Invited Review for the Journal "Advances in
Astronomy"; references adde
Baryons Still Trace Dark Matter: Probing CMB Lensing Maps For Hidden Isocurvature
Compensated isocurvature perturbations (CIPs) are primordial fluctuations that balance baryon and dark-matter isocurvature to leave the total matter density unperturbed. The effects of CIPs on the cosmic microwave background (CMB) anisotropies are similar to those produced by weak lensing of the CMB: smoothing of the power spectrum and generation of non-Gaussian features. Here, an entirely new CIP contribution to the standard estimator for the lensing-potential power spectrum is derived. Planck measurements of the temperature and polarization power spectrum, as well as estimates of CMB lensing, are used to place limits on the variance of the CIP fluctuations on CMB scales, Δ2rms(RCMB). The resulting constraint of Δ2rms(RCMB)\u3c4.3×10−3 at 95% confidence level (CL) using this new technique improves on past work by a factor of ∼3. We find that for Planck data our constraints almost reach the sensitivity of the optimal CIP estimator. The method presented here is currently the most sensitive probe of the amplitude of a scale-invariant CIP power spectrum, ACIP, placing an upper limit of ACIP\u3c0.017 at 95% CL. Future measurements of the large-scale CMB lensing-potential power spectrum could probe CIP amplitudes as low as Δ2rms(RCMB)=8×10−5 at 95% CL (corresponding to ACIP=3.2×10−4)
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