33 research outputs found
Moment transport equations for the primordial curvature perturbation
In a recent publication, we proposed that inflationary perturbation theory
can be reformulated in terms of a probability transport equation, whose moments
determine the correlation properties of the primordial curvature perturbation.
In this paper we generalize this formulation to an arbitrary number of fields.
We deduce ordinary differential equations for the evolution of the moments of
zeta on superhorizon scales, which can be used to obtain an evolution equation
for the dimensionless bispectrum, fNL. Our equations are covariant in field
space and allow identification of the source terms responsible for evolution of
fNL. In a model with M scalar fields, the number of numerical integrations
required to obtain solutions of these equations scales like O(M^3). The
performance of the moment transport algorithm means that numerical calculations
with M >> 1 fields are straightforward. We illustrate this performance with a
numerical calculation of fNL in Nflation models containing M ~ 10^2 fields,
finding agreement with existing analytic calculations. We comment briefly on
extensions of the method beyond the slow-roll approximation, or to calculate
higher order parameters such as gNL.Comment: 23 pages, plus appendices and references; 4 figures. v2: incorrect
statements regarding numerical delta N removed from Sec. 4.3. Minor
modifications elsewher
On the modelling of the excesses of galaxy clusters over high-mass thresholds
In this work we present for the first time an application of the Pareto
approach to the modelling of the excesses of galaxy clusters over high-mass
thresholds. The distribution of those excesses can be described by the
generalized Pareto distribution (GPD), which is closely related to the
generalized extreme value (GEV) distribution. After introducing the formalism,
we study the impact of different thresholds and redshift ranges on the
distributions, as well as the influence of the survey area on the mean excess
above a given mass threshold. We also show that both the GPD and the GEV
approach lead to identical results for rare, thus high-mass and high-redshift,
clusters. As an example, we apply the Pareto approach to ACT-CL J0102-4915 and
SPT-CL J2106-5844 and derive the respective cumulative distribution functions
of the exceedance over different mass thresholds. We also study the possibility
to use the GPD as a cosmological probe. Since in the maximum likelihood
estimation of the distribution parameters all the information from clusters
above the mass threshold is used, the GPD might offer an interesting
alternative to GEV-based methods that use only the maxima in patches. When
comparing the accuracy with which the parameters can be estimated, it turns out
that the patch-based modelling of maxima is superior to the Pareto approach. In
an ideal case, the GEV approach is capable to estimate the location parameter
with a percent level precision for less than 100 patches. This result makes the
GEV based approach potentially also interesting for cluster surveys with a
smaller area.Comment: 10 pages, 8 figures, MNRAS accepted, minor modifications to match the
accepted versio
Scale Dependence of the Halo Bias in General Local-Type Non-Gaussian Models I: Analytical Predictions and Consistency Relations
We investigate the clustering of halos in cosmological models starting with
general local-type non-Gaussian primordial fluctuations. We employ multiple
Gaussian fields and add local-type non-Gaussian corrections at arbitrary order
to cover a class of models described by frequently-discussed f_nl, g_nl and
\tau_nl parameterization. We derive a general formula for the halo power
spectrum based on the peak-background split formalism. The resultant spectrum
is characterized by only two parameters responsible for the scale-dependent
bias at large scale arising from the primordial non-Gaussianities in addition
to the Gaussian bias factor. We introduce a new inequality for testing
non-Gaussianities originating from multi fields, which is directly accessible
from the observed power spectrum. We show that this inequality is a
generalization of the Suyama-Yamaguchi inequality between f_nl and \tau_nl to
the primordial non-Gaussianities at arbitrary order. We also show that the
amplitude of the scale-dependent bias is useful to distinguish the simplest
quadratic non-Gaussianities (i.e., f_nl-type) from higher-order ones (g_nl and
higher), if one measures it from multiple species of galaxies or clusters of
galaxies. We discuss the validity and limitations of our analytic results by
comparison with numerical simulations in an accompanying paper.Comment: 25 pages, 3 figures, typo corrected, Appendix C updated, submitted to
JCA
Scale-dependent bias from the primordial non-Gaussianity with a Gaussian-squared field
We investigate the halo bias in the case where the primordial curvature
fluctuations, , are sourced from both a Gaussian random field and a
Gaussian-squared field, as , so-called "ungaussiton model". We employ the
peak-background split formula and find a new scale-dependence in the halo bias
induced from the Gaussian-squared field.Comment: 9 pages, 1 figure, comments are welcom
Primordial Black Holes, Eternal Inflation, and the Inflationary Parameter Space after WMAP5
We consider constraints on inflation driven by a single, minimally coupled
scalar field in the light of the WMAP5 dataset, as well as ACBAR and the
SuperNova Legacy Survey. We use the Slow Roll Reconstruction algorithm to
derive optimal constraints on the inflationary parameter space. The scale
dependence in the slope of the scalar spectrum permitted by WMAP5 is large
enough to lead to viable models where the small scale perturbations have a
substantial amplitude when extrapolated to the end of inflation. We find that
excluding parameter values which would cause the overproduction of primordial
black holes or even the onset of eternal inflation leads to potentially
significant constraints on the slow roll parameters. Finally, we present a more
sophisticated approach to including priors based on the total duration of
inflation, and discuss the resulting restrictions on the inflationary parameter
space.Comment: v2: version published in JCAP. Minor clarifications and references
adde
New Solutions of the Inflationary Flow Equations
The inflationary flow equations are a frequently used method of surveying the
space of inflationary models. In these applications the infinite hierarchy of
differential equations is truncated in a way which has been shown to be
equivalent to restricting the set of models considered to those characterized
by polynomial inflaton potentials. This paper explores a different method of
solving the flow equations, which does not truncate the hierarchy and in
consequence covers a much wider class of models while retaining the practical
usability of the standard approach.Comment: References added, and a couple of comment
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
COrE (Cosmic Origins Explorer) A White Paper
COrE (Cosmic Origins Explorer) is a fourth-generation full-sky,
microwave-band satellite recently proposed to ESA within Cosmic Vision
2015-2025. COrE will provide maps of the microwave sky in polarization and
temperature in 15 frequency bands, ranging from 45 GHz to 795 GHz, with an
angular resolution ranging from 23 arcmin (45 GHz) and 1.3 arcmin (795 GHz) and
sensitivities roughly 10 to 30 times better than PLANCK (depending on the
frequency channel). The COrE mission will lead to breakthrough science in a
wide range of areas, ranging from primordial cosmology to galactic and
extragalactic science. COrE is designed to detect the primordial gravitational
waves generated during the epoch of cosmic inflation at more than
for . It will also measure the CMB gravitational lensing
deflection power spectrum to the cosmic variance limit on all linear scales,
allowing us to probe absolute neutrino masses better than laboratory
experiments and down to plausible values suggested by the neutrino oscillation
data. COrE will also search for primordial non-Gaussianity with significant
improvements over Planck in its ability to constrain the shape (and amplitude)
of non-Gaussianity. In the areas of galactic and extragalactic science, in its
highest frequency channels COrE will provide maps of the galactic polarized
dust emission allowing us to map the galactic magnetic field in areas of
diffuse emission not otherwise accessible to probe the initial conditions for
star formation. COrE will also map the galactic synchrotron emission thirty
times better than PLANCK. This White Paper reviews the COrE science program,
our simulations on foreground subtraction, and the proposed instrumental
configuration.Comment: 90 pages Latex 15 figures (revised 28 April 2011, references added,
minor errors corrected
The Hierarchical Structure and Dynamics of Voids
Contrary to the common view voids have very complex internal structure and
dynamics. Here we show how the hierarchy of structures in the density field
inside voids is reflected by a similar hierarchy of structures in the velocity
field. Voids defined by dense filaments and clusters can de described as simple
expanding domains with coherent flows everywhere except at their boundaries. At
scales smaller that the void radius the velocity field breaks into expanding
sub-domains corresponding to sub- voids. These sub-domains break into even
smaller sub-sub domains at smaller scales resulting in a nesting hierarchy of
locally expanding domains. The ratio between the magnitude of the velocity
field responsible for the expansion of the void and the velocity field defining
the sub voids is approximately one order of magnitude. The small-scale
components of the velocity field play a minor role in the shaping of the voids
but they define the local dynamics directly affecting the processes of galaxy
formation and evolution. The super-Hubble expansion inside voids makes them
cosmic magnifiers by stretching their internal primordial density fluctuations
allowing us to probe the small scales in the primordial density field. Voids
also act like time machines by "freezing" the development of the medium-scale
density fluctuations responsible for the formation of the tenuous web of
structures seen connecting proto galaxies in computer simulations. As a result
of this freezing haloes in voids can remain "connected" to this tenuous web
until the present time. This may have an important effect in the formation and
evolution of galaxies in voids by providing an efficient gas accretion
mechanism via coherent low-velocity streams that can keep a steady inflow of
matter for extended periods of time.Comment: High-res version are related media here:
http://skysrv.pha.jhu.edu/~miguel/Papers/Hierarchy_voids/index.htm