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Pamela Launches
Constraining Primordial Non-Gaussianities from the WMAP2 2-1
Cumulant Correlator Power Spectrum
Authors:
Gang
Chen, Istvan
Szapudi
Comments: 4 pages,2 figures; typos corrected, references changed
We measure the 2-1 cumulant correlator power spectrum $C^{21}_l$, a
degenerate bispectrum, from the second data release of the Wilkinson
Microwave
Anisotropy Probe (WMAP). Our high resolution measurements with SpICE
span a
large configuration space ($\simeq 168\times999$) corresponding to the
possible
cross-correlations of the maps recorded by the different differencing
assemblies. We present a novel method to recover the eigenmodes of the
correspondingly large Monte Carlo covariance matrix. We examine its
eigenvalue
spectrum and use random matrix theory to show that the off diagonal
terms are
dominated by noise. We minimize the $\chi^2$ to obtain constraints for
the
non-linear coupling parameter $f_{NL} = 22 \pm 52 (1\sigma)$.
Estimators for local non-Gaussianities
Authors:
Paolo
Creminelli (ICTP, Trieste), Leonardo
Senatore (MIT), Matias
Zaldarriaga (Harvard-Smithsonian Ctr. Astrophys. & Harvard U.,
Phys. Dept.)
Comments: 25 pages
Report-no: HUTP-06/A0016, MIT-CTP 3737, IC/2006/028
We study the Likelihood function of data given f_NL for the so-called
local
type of non-Gaussianity. In this case the curvature perturbation is a
non-linear function, local in real space, of a Gaussian random field.
We
compute the Cramer-Rao bound for f_NL and show that for small values of
f_NL
the 3-point function estimator saturates the bound and is equivalent to
calculating the full Likelihood of the data. However, for sufficiently
large
f_NL, the naive 3-point function estimator has a much larger variance
than
previously thought. In the limit in which the departure from
Gaussianity is
detected with high confidence, error bars on f_NL only decrease as 1/ln
Npix
rather than Npix^-1/2 as the size of the data set increases. We
identify the
physical origin of this behavior and explain why it only affects the
local type
of non-Gaussianity, where the contribution of the first multipoles is
always
relevant. We find a simple improvement to the 3-point function
estimator that
makes the square root of its variance decrease as Npix^-1/2 even for
large
f_NL, asymptotically approaching the Cramer-Rao bound. We show that
using the
modified estimator is practically equivalent to computing the full
Likelihood
of f_NL given the data. Thus other statistics of the data, such as the
4-point
function and Minkowski functionals, contain no additional information
on f_NL.
In particular, we explicitly show that the recent claims about the
relevance of
the 4-point function are not correct. By direct inspection of the
Likelihood,
we show that the data do not contain enough information for any
statistic to be
able to constrain higher order terms in the relation between the
Gaussian field
and the curvature perturbation, unless these are orders of magnitude
larger
than the size suggested by the current limits on f_NL.
Transients from Initial Conditions in Cosmological Simulations
Authors:
M.
Crocce, S.
Pueblas, R.
Scoccimarro
Comments: 14 pages, 14 figures, code to generate 2LPT initial
conditions available at this
http URL
We study the impact of setting initial conditions in numerical
simulations
using the standard procedure based on the Zel'dovich approximation
(ZA). As it
is well known from perturbation theory, ZA initial conditions have
incorrect
second and higher-order growth and therefore excite long-lived
transients in
the evolution of the statistical properties of density and velocity
fields. We
also study the improvement brought by using more accurate initial
conditions
based on second-order Lagrangian perturbation theory (2LPT). We show
that 2LPT
initial conditions reduce transients significantly and thus are much
more
appropriate for numerical simulations devoted to precision cosmology.
Using
controlled numerical experiments with ZA and 2LPT initial conditions we
show
that simulations started at redshift z_i=49 using the ZA underestimate
the
power spectrum in the nonlinear regime by about 2,4,8 % at z=0,1,3
respectively, whereas the mass function of dark matter halos is
underestimated
by 5% at m=10^15 M_sun/h (z=0) and 10% at m=2x10^14M_sun/h (z=1). The
clustering of halos is also affected to the few percent level at z=0.
These
systematics effects are typically larger than statistical uncertainties
in
recent mass function and power spectrum fitting formulae extracted from
numerical simulations. At large scales, the measured transients in
higher-order
correlations can be understood from first principle calculations based
on
perturbation theory.
Cosmological Constraints from the Red-Sequence Cluster Survey
Authors:
Michael
D. Gladders, H.K.C.
Yee, Subhabrata
Majumdar, L.
Felipe Barrientos, Henk
Hoekstra, Patrick
B. Hall, Leopoldo
Infante
Comments: 18 pages, 4 figures, 3 tables
[abridged] We present a first cosmological analysis of a refined
cluster
catalog from the Red-Sequence Cluster Survey (RCS). The input cluster
sample is
derived from 72.07 square degrees of imaging data [...] The catalog
contains
956 clusters over 0.35<z<0.95, limited by cluster richness and
richness error.
The calibration of the survey images has been extensively cross-checked
against
publicly available Sloan Digital Sky Survey imaging [...] We analyze
the
cluster sample via a general self-calibration technique including
scatter in
the mass-richness relation [...]. We fit simultaneously for Omega_M and
sigma_8, and four parameters describing the calibration of cluster
richness to
mass, its evolution with redshift, and scatter in the richness-mass
relation.
The principal goal of this general analysis is to establish the
consistency (or
lack thereof) between the fitted parameters (both cosmological and
cluster mass
observables) and available results on both from independent measures.
From an
unconstrained analysis, Omega_M and sigma_8 are 0.31+0.11-0.10 and
0.67+0.18-0.13 respectively. An analysis including Gaussian priors on
the slope
and zeropoint of the mass-richness relation gives very similar results:
0.30+0.12-0.11 and 0.70+0.27-0.15. Both analyses are in good agreement
with the
current literature. The parameters describing the mass-richness
relation in the
unconstrained fit are also eminently reasonable and agree with existing
follow-up data on both the RCS-1 and other cluster samples. Our results
directly demonstrate that future surveys (optical and otherwise), with
much
larger samples of clusters, can give constraints competitive with other
probes
of cosmology.
The Virial Mass Function of Nearby SDSS Galaxy Clusters
Authors:
Kenneth
Rines (Yale/YCAA), Antonaldo
Diaferio (Torino), Priyamvada
Natarajan (Yale/YCAA)
Comments: 22 pages, 11 figures, submitted to ApJ
We present a new determination of the cluster mass function and
velocity
dispersion function in a volume $\sim10^7 h^3$Mpc$^{-3}$ using the
Fourth Data
Release of the Sloan Digital Sky Survey (SDSS). We use the caustic
technique to
remove foreground and background galaxies. The cluster virial mass
function
agrees very well with recent estimates from both X-ray observations and
cluster
richnesses. The mass function lies between those predicted by the
First-Year
and Three-Year WMAP data. We constrain the cosmological parameters
$\Omega_m$
and $\sigma_8$ and find good agreement with WMAP and constraints from
other
techniques. With the CIRS mass function alone, we estimate
$\Omega_m=0.23^{+0.14}_{-0.09}$ and $\sigma_8=0.91^{+0.17}_{-0.19}$, or
$\sigma_8=0.81\pm$0.03 when holding $\Omega_m=0.3$ fixed. We also use
the WMAP
parameters as priors and constrain velocity segregation in clusters.
Using the
First and Third-Year results, we infer velocity segregation of
$\sigma_{gxy}/\sigma_{DM}\approx0.91\pm$0.04 or 1.30$\pm$0.05
respectively. We
compare the velocity dispersion function of clusters to that of
early-type
galaxies and conclude that clusters comprise the high-velocity end of
the
velocity dispersion function of dark matter haloes. The evolution of
cluster
abundances provides constraints on dark energy models; the mass
function
presented here offers an important low redshift calibration benchmark.
Inflation and WMAP three year data: Features have a Future!
Authors:
Laura
Covi, Jan
Hamann, Alessandro
Melchiorri, Anze
Slosar, Irene
Sorbera
Comments: 7 pages, 11 figures
Report-no: DESY 06-089
The new three year WMAP data seem to confirm the presence of
non-standard
large scale features in the Cosmic Microwave Anisotropies power
spectrum. While
these features may hint at uncorrected experimental systematics, it is
also
possible to generate, in a cosmological way, oscillations on large
angular
scales by introducing a sharp step in the inflaton potential. Using
current
cosmological data, we derive constraints on the position, magnitude and
gradient of a possible step in the inflaton potential. We show that a
step in
the potential, while strongly constrained by current data, is still
allowed and
may provide an interesting explanation to the currently measured
deviations
from the standard featureless spectrum.
Difficulties for Compact Composite Object Dark Matter
Authors:
Daniel
T. Cumberbatch, Joseph
Silk, Glenn
D. Starkman
Recently Zhitnitsky suggested ``that DM particles are strongly
interacting
composite macroscopically large objects ... made of well known light
quarks (or
>... antiquarks)." In doing so he argued that these compact
composite objects
(CCOs) are ``natural explanations of many observed data, such as [the]
511 keV
line from the bulge of our galaxy" and the CHANDRA-observed excess of
diffuse
X-ray emission toward the galactic center. Here we argue that the
annihilation
of interstellar electrons (or positrons) off positrons (or electrons)
in the
the CCO does not lead to the observed narrow 511 keV line, but to a
broad
continuum due to the high densities of the CCO-confined leptons. We
argue
further that in order to generate the observed flux of X-rays, the CCOs
in the
galactic centre would only require a temperature of 1 eV, and therefore
unlikely to be the dominant heat source for the surrounding 8 keV
plasma. While
these observations do not rule out CCOs as galactic dark matter, they
do weaken
the motivation for them.
The Price of WMAP Inflation in Supergravity
Authors:
J.
Ellis, Z.
Lalak, S.
Pokorski, K.
Turzynski
Comments: 15 pages, 6 figures, plain Latex
Report-no: CERN-PH-TH/2006-099
The three-year data from WMAP are in stunning agreement with the
simplest
possible quadratic potential for chaotic inflation, as well as with new
or
symmetry-breaking inflation. We investigate the possibilities for
incorporating
these potentials within supergravity, particularly of the no-scale type
that is
motivated by string theory. Models with inflation driven by the matter
sector
may be constructed in no-scale supergravity, if the moduli are assumed
to be
stabilised by some higher-scale dynamics and at the expense of some
fine-tuning. We discuss specific scenarios for stabilising the moduli
via
either D- or F-terms in the effective potential, and survey possible
inflationary models in the presence of D-term stabilisation.
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