30 research outputs found
The radiative transfer for polarized radiation at second order in cosmological perturbations
This article investigates the full Boltzmann equation up to second order in
the cosmological perturbations. Describing the distribution of polarized
radiation by using a tensor valued distribution function, the second order
Boltzmann equation, including polarization, is derived without relying on the
Stokes parameters.Comment: 4 pages, no figure; replaced to match published versio
The shape of the CMB lensing bispectrum
Lensing of the CMB generates a significant bispectrum, which should be
detected by the Planck satellite at the 5-sigma level and is potentially a
non-negligible source of bias for f_NL estimators of local non-Gaussianity. We
extend current understanding of the lensing bispectrum in several directions:
(1) we perform a non-perturbative calculation of the lensing bispectrum which
is ~10% more accurate than previous, first-order calculations; (2) we
demonstrate how to incorporate the signal variance of the lensing bispectrum
into estimates of its amplitude, providing a good analytical explanation for
previous Monte-Carlo results; and (3) we discover the existence of a
significant lensing bispectrum in polarization, due to a previously-unnoticed
correlation between the lensing potential and E-polarization as large as 30% at
low multipoles. We use this improved understanding of the lensing bispectra to
re-evaluate Fisher-matrix predictions, both for Planck and cosmic variance
limited data. We confirm that the non-negligible lensing-induced bias for
estimation of local non-Gaussianity should be robustly treatable, and will only
inflate f_NL error bars by a few percent over predictions where lensing effects
are completely ignored (but note that lensing must still be accounted for to
obtain unbiased constraints). We also show that the detection significance for
the lensing bispectrum itself is ultimately limited to 9 sigma by cosmic
variance. The tools that we develop for non-perturbative calculation of the
lensing bispectrum are directly relevant to other calculations, and we give an
explicit construction of a simple non-perturbative quadratic estimator for the
lensing potential and relate its cross-correlation power spectrum to the
bispectrum. Our numerical codes are publicly available as part of CAMB and
LensPix.Comment: 32 pages, 10 figures; minor changes to match JCAP-accepted version.
CMB lensing and primordial local bispectrum codes available as part of CAMB
(http://camb.info/
Running spectral index from shooting-star moduli
We construct an inflationary model that is consistent with both large
non-Gaussianity and a running spectral index. The scenario of modulated
inflation suggests that modulated perturbation can induce the curvature
perturbation with a large non-Gaussianity, even if the inflaton perturbation is
negligible. Using this idea, we consider a multi-field extension of the
modulated inflation scenario and examine the specific situation where different
moduli are responsible for the perturbation at different scales. We suppose
that the additional moduli (shooting-star moduli) is responsible for the
curvature perturbation at the earlier inflationary epoch and it generates the
fluctuation with n>1 spectral index at this scale. After a while, another
moduli (or inflaton) takes the place and generates the perturbation with n<1.
At the transition point the two fluctuations are comparable with each other. We
show how the spectral index is affected by the transition induced by the
shooting-star moduli.Comment: 14 pages, latex, accepted for publication in JHE
ISS-flation
Inflation may occur while rolling into the metastable supersymmetry-breaking
vacuum of massive supersymmetric QCD. We explore the range of parameters in
which slow-roll inflation and long-lived metastable supersymmetry breaking may
be simultaneously realized. The end of slow-roll inflation in this context
coincides with the spontaneous breaking of a global symmetry, which may give
rise to significant curvature perturbations via inhomogenous preheating. Such
spontaneous symmetry breaking at the end of inflation may give rise to
observable non-gaussianities, distinguishing this scenario from more
conventional models of supersymmetric hybrid inflation.Comment: 26 page
Cosmological Parameters Degeneracies and Non-Gaussian Halo Bias
We study the impact of the cosmological parameters uncertainties on the
measurements of primordial non-Gaussianity through the large-scale non-Gaussian
halo bias effect. While this is not expected to be an issue for the standard
LCDM model, it may not be the case for more general models that modify the
large-scale shape of the power spectrum. We consider the so-called local
non-Gaussianity model and forecasts from planned surveys, alone and combined
with a Planck CMB prior. In particular, we consider EUCLID- and LSST-like
surveys and forecast the correlations among and the running of the
spectral index , the dark energy equation of state , the effective
sound speed of dark energy perturbations , the total mass of massive
neutrinos , and the number of extra relativistic degrees of
freedom . Neglecting CMB information on and scales /Mpc, we find that, if is assumed to be known, the
uncertainty on cosmological parameters increases the error on by
10 to 30% depending on the survey. Thus the constraint is
remarkable robust to cosmological model uncertainties. On the other hand, if
is simultaneously constrained from the data, the
error increases by . Finally, future surveys which provide a large
sample of galaxies or galaxy clusters over a volume comparable to the Hubble
volume can measure primordial non-Gaussianity of the local form with a
marginalized 1-- error of the order , after
combination with CMB priors for the remaining cosmological parameters. These
results are competitive with CMB bispectrum constraints achievable with an
ideal CMB experiment.Comment: 17 pages, 1 figure added, typos corrected, comments added, matches
the published versio
Non-Gaussian isocurvature perturbations in dark radiation
We study non-Gaussian properties of the isocurvature perturbations in the
dark radiation, which consists of the active neutrinos and extra light species,
if exist. We first derive expressions for the bispectra of primordial
perturbations which are mixtures of curvature and dark radiation isocurvature
perturbations. We also discuss CMB bispectra produced in our model and forecast
CMB constraints on the nonlinearity parameters based on the Fisher matrix
analysis. Some concrete particle physics motivated models are presented in
which large isocurvature perturbations in extra light species and/or the
neutrino density isocurvature perturbations as well as their non-Gaussianities
may be generated. Thus detections of non-Gaussianity in the dark radiation
isocurvature perturbation will give us an opportunity to identify the origin of
extra light species and lepton asymmetry.Comment: 32 pages, 7 figure
Constraining Running Non-Gaussianity
The primordial non-Gaussian parameter fNL has been shown to be
scale-dependent in several models of inflation with a variable speed of sound.
Starting from a simple ansatz for a scale-dependent amplitude of the primordial
curvature bispectrum for two common phenomenological models of primordial
non-Gaussianity, we perform a Fisher matrix analysis of the bispectra of the
temperature and polarization of the Cosmic Microwave Background (CMB) radiation
and derive the expected constraints on the parameter nNG that quantifies the
running of fNL(k) for current and future CMB missions such as WMAP, Planck and
CMBPol. We find that CMB information alone, in the event of a significant
detection of the non-Gaussian component, corresponding to fNL = 50 for the
local model and fNL = 100 for the equilateral model of non-Gaussianity, is able
to determine nNG with a 1-sigma uncertainty of Delta nNG = 0.1 and Delta nNG =
0.3, respectively, for the Planck mission. In addition, we consider a Fisher
matrix analysis of the galaxy power spectrum to determine the expected
constraints on the running parameter nNG for the local model and of the galaxy
bispectrum for the equilateral model from future photometric and spectroscopic
surveys. We find that, in both cases, large-scale structure observations should
achieve results comparable to or even better than those from the CMB, while
showing some complementarity due to the different distribution of the
non-Gaussian signal over the relevant range of scales. Finally, we compare our
findings to the predictions on the amplitude and running of non-Gaussianity of
DBI inflation, showing how the constraints on a scale-dependent fNL(k)
translate into constraints on the parameter space of the theory.Comment: 37 pages, 14 figure
Scale-dependent non-Gaussianity probes inflationary physics
We calculate the scale dependence of the bispectrum and trispectrum in
(quasi) local models of non-Gaussian primordial density perturbations, and
characterize this scale dependence in terms of new observable parameters. They
can help to discriminate between models of inflation, since they are sensitive
to properties of the inflationary physics that are not probed by the standard
observables. We find consistency relations between these parameters in certain
classes of models. We apply our results to a scenario of modulated reheating,
showing that the scale dependence of non-Gaussianity can be significant. We
also discuss the scale dependence of the bispectrum and trispectrum, in cases
where one varies the shape as well as the overall scale of the figure under
consideration. We conclude providing a formulation of the curvature
perturbation in real space, which generalises the standard local form by
dropping the assumption that f_NL and g_NL are constants.Comment: 27 pages, 2 figures. v2: Minor changes to match the published versio
Signatures of Initial State Modifications on Bispectrum Statistics
Modifications of the initial-state of the inflaton field can induce a
departure from Gaussianity and leave a testable imprint on the higher order
correlations of the CMB and large scale structures in the Universe. We focus on
the bispectrum statistics of the primordial curvature perturbation and its
projection on the CMB. For a canonical single-field action the three-point
correlator enhancement is localized, maximizing in the collinear limit,
corresponding to enfolded or squashed triangles in comoving momentum space. We
show that the available local and equilateral template are very insensitive to
this localized enhancement and do not generate noteworthy constraints on
initial-state modifications. On the other hand, when considering the addition
of a dimension 8 higher order derivative term, we find a dominant rapidly
oscillating contribution, which had previously been overlooked and whose
significantly enhanced amplitude is independent of the triangle under
consideration. Nevertheless, the oscillatory nature of (the sign of) the
correlation function implies the signal is nearly orthogonal to currently
available observational templates, strongly reducing the sensitivity to the
enhancement. Constraints on departures from the standard Bunch-Davies vacuum
state can be derived, but also depend on the next-to-leading terms. We
emphasize that the construction and application of especially adapted templates
could lead to CMB bispectrum constraints on modified initial states already
competing with those derived from the power spectrum.Comment: 41 pages, 7 figures, 2 appendices. Added some clarifications and
comments, additional references, to appear in JCA
An overview of the current status of CMB observations
In this paper we briefly review the current status of the Cosmic Microwave
Background (CMB) observations, summarising the latest results obtained from CMB
experiments, both in intensity and polarization, and the constraints imposed on
the cosmological parameters. We also present a summary of current and future
CMB experiments, with a special focus on the quest for the CMB B-mode
polarization.Comment: Latest CMB results have been included. References added. To appear in
"Highlights of Spanish Astrophysics V", Proceedings of the VIII Scientific
Meeting of the Spanish Astronomical Society (SEA) held in Santander, 7-11
July, 200