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03 Apr 2006
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13 Mar 2006
6 Mar 2006
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Potential sources of contamination to weak lensing
measurements: constraints from N-body simulations
Authors:
Catherine
Heymans, Martin
White, Alan
Heavens, Chris
Vale, Ludovic
Van Waerbeke
Comments: 11 pages, 10 figures, submitted to MNRAS
We investigate the expected correlation between the weak gravitational
shear
of distant galaxies and the orientation of foreground galaxies, through
the use
of numerical simulations. This shear-ellipticity correlation can mimic
a
cosmological weak lensing signal, and is potentially the limiting
physical
systematic effect for cosmology with future high-precision weak lensing
surveys. We find that, if uncorrected, the shear-ellipticity
correlation could
contribute up to 10% of the weak lensing signal on scales up to 20
arcminutes,
for lensing surveys with a median depth z=1. The most massive
foreground
galaxies are expected to cause the largest correlations, a result also
seen in
the Sloan Digital Sky Survey. We find that the redshift dependence of
the
effect is proportional to the lensing efficiency of the foreground, and
this
offers prospects for removal to high precision, although with some
model
dependence. The contamination is characterised by a weakly negative
B-mode,
which can be used as a diagnostic of systematic errors. We also provide
more
accurate predictions for a second potential source of error, the
intrinsic
alignment of nearby galaxies. This source of contamination is less
important,
however, as it can be easily removed with distance information.
Perturbation Theory Reloaded: Analytical Calculation of
Non-linearity in Baryonic Oscillations in the Real Space Matter Power
Spectrum
Authors:
Donghui
Jeong, Eiichiro
Komatsu (Univ. of Texas at Austin)
Comments: 5 pages, 3 figures, submitted to ApJ
We compare the non-linear matter power spectrum in real space
calculated
analytically from 3rd-order perturbation theory with N-body simulations
at
1<z<6. We find that the perturbation theory prediction agrees
with the
simulations to better than 1% accuracy in the weakly non-linear regime
where
the dimensionless power spectrum, Delta^2(k)=k^3P(k)/2pi^2, which
approximately
gives variance of matter density field at a given k, is less than 0.4.
While
the baryonic acoustic oscillation features are preserved in the weakly
non-linear regime at z>1, the shape of oscillations is distorted
from the
linear theory prediction. Nevertheless, our results suggest that one
can
correct the distortion caused by non-linearity almost exactly. We also
find
that perturbation theory, which does not contain any free parameters,
provides
a significantly better fit to the simulations than the conventional
approaches
based on empirical fitting functions to simulations. The future work
would
include perturbation theory calculations of non-linearity in redshift
space
distortion and halo biasing in the weakly non-linear regime.
Gravitino Overproduction in Inflaton Decay
Authors:
Masahiro
Kawasaki, Fuminobu
Takahashi, T.
T. Yanagida
Comments: 13 pages, 1 figure
Report-no: DESY 06-034
Most of the inflation models end up with non-vanishing vacuum
expectation
values of the inflaton fields \phi in the true vacuum, which induce, in
general, nonvanishing auxiliary field G_\phi for the inflaton potential
in
supergravity. We show that the presence of nonzero G_\phi gives rise to
inflaton decay into a pair of the gravitinos and are thereby severely
constrained by cosmology. For several inflation models, we explicitly
calculate
the values of G_\phi and find that most of them are excluded or on the
verge of
being excluded. We conclude that an inflation model with vanishing
G_\phi,
typically realized in a chaotic inflation, is favored in a sense that
it
naturally avoids the potential gravitino overproduction problem.
Cosmic Conspiracies
Authors:
Douglas
Scott, Ali
Frolop
Comments: 2 pages
The now standard vanilla-flavoured LambdaCDM model has gained further
confirmation with the release of the 3-year WMAP data combined with
several
other cosmological data-sets. As the parameters of this standard model
become
known with increasing precision, more of its bizarre features become
apparent.
Here we describe some of the strangest of these ostensible
coincidences. In
particular we appear to live (within 1sigma) at the precise epoch when
the age
of the Universe multiplied by the Hubble parameter H_0 t_0 = 1.
B polarization of cosmic microwave background as a tracer of
strings
Authors:
Uros
Seljak, Anze
Slosar
Comments: 6 pages, 1 figure, 1 table
String models can produce successful inflationary scenarios in the
context of
brane collisions and in many of these models cosmic strings may also be
produced. In scenarios such as KKLMMT the string contribution is
naturally
predicted to be well below the inflationary signal for cosmic microwave
background (CMB) temperature anisotropies, in agreement with the
existing
limits. We find that for $B$ type polarization of CMB the situation is
reversed
and the dominant signal comes from vector modes generated by cosmic
strings,
which exceeds the gravity wave signal from both inflation and strings.
The
signal can be detected for a broad range of parameter space: future
polarization experiments may be able to detect the string signal down
to the
string tension $G\mu=10^{-9}$, although foregrounds and lensing are
likely to
worsen these limits. We argue that the optimal scale to search for the
string
signature is at $\ell\sim 1000$, but in models with high optical depth
the
signal from reionization peak at large scales is also significant. The
shape of
the power spectrum allows one to distinguish the string signature from
the
gravity waves from inflation, but only with a sufficiently high angular
resolution experiment
Mini-halo disruption due to encounters with stars
Authors:
Anne
M. Green, Simon
P. Goodwin
Comments: 10 pages, 7 figures
We study the energy loss and disruption of dark matter mini-halos due
to
interactions with stars. We find that the fractional energy loss in
simulations
agrees well with the analytic impulse approximation for small and large
impact
parameters, with a rapid transition between these two regimes. The
fractional
energy loss at large impact parameters is fairly independent of the
mass and
density profile of the mini-halo, however low-mass mini-halos lose a
greater
fraction of their energy in close encounters. We formulate new fitting
functions that match these results and use them to estimate the
disruption
timescales, taking into account the stellar velocity and mass
distributions.
For mini-halos with mass $M< {\cal O}(10^{-7} M_{\odot})$ on typical
orbits
which pass through the disc, we find that the disruption timescales are
independent of mass and of order the age of the Milky Way. For more
massive
mini-halos the disruption timescales increase rapidly with increasing
mass.
Finally, we point out that the fractional energy loss is dependent on
the,
somewhat arbitrary, definition of the mini-halo radius and argue that a
full
calculation of the mini-halo survival probability will have to
incorporate
energy loss due to encounters with stars and tidal stripping in a
single
consistent calculation.
The First Stars in The Universe
Authors:
Smadar
Naoz (1), Shay
Noter (1), Rennan
Barkana (1) ((1) Tel Aviv University)
Comments: 4 pages, 3 figures, submitted to PRL
Large telescopes have allowed astronomers to observe galaxies that
formed as
early as 850 million years after the Big Bang. We predict when the
first galaxy
that astronomers can observe formed in the universe, accounting for the
first
time for the size of the universe and for three essential ingredients:
the
light travel time from distant galaxies, Poisson and density
fluctuations on
all scales, and the effect of very early cosmic history on galaxy
formation. We
find that the first observable star is most likely to have formed 30
million
years after the Big Bang (at redshift 65), much earlier than previously
expected. Also, the first galaxy as massive as our own Milky Way likely
formed
when the universe was only 400 Myr old. We also show that significant
modifications are required in current methods of numerically simulating
the
formation of the first galaxies.
X-ray and Sunyaev-Zel'dovich Effect Measurements of the Gas
Mass Fraction in Galaxy Clusters
Authors:
S.
LaRoque, M.
Bonamente, J.
Carlstrom, M.
Joy, D.
Nagai, E.
Reese, K.
Dawson
Comments: ApJ, submitted. 47 pages, 5 figures, 8 tables
We present gas mass fractions of 38 massive galaxy clusters spanning
redshifts from 0.14 to 0.89, derived from Chandra X-ray data and
OVRO/BIMA
interferometric Sunyaev-Zel'dovich Effect measurements. We use three
models for
the gas distribution: (1) an isothermal beta-model fit jointly to the
X-ray
data at radii beyond 100 kpc and to all of the SZE data,(2) a
non-isothermal
double beta-model fit jointly to all of the X-ray and SZE data, and (3)
an
isothermal beta-model fit only to the SZE spatial data. We show that
the simple
isothermal model well characterizes the intracluster medium (ICM)
outside of
the cluster core in clusters with a wide range of morphological
properties. The
X-ray and SZE determinations of mean gas mass fractions for the 100
kpc-cut
isothermal beta-model are fgas(X-ray)=0.110 +0.003-0.003 +0.006-0.018
and
fgas(SZE)=0.116 +0.005-0.005 +0.009-0.026, where uncertainties are
statistical
followed by systematic at 68% confidence. For the non-isothermal double
beta-model, fgas(X-ray)=0.119 +0.003-0.003 +0.007-0.014 and
fgas(SZE)=0.121
+0.005-0.005 +0.009-0.016. For the SZE-only model, fgas(SZE)=0.120
+0.009-0.009
+0.009-0.027. Our results indicate that the ratio of the gas mass
fraction
within r2500 to the cosmic baryon fraction is 0.68 +0.10-0.16 where the
range
includes statistical and systematic uncertainties. By assuming that
cluster gas
mass fractions are independent of redshift, we find that the results
are in
agreement with standard LambdaCDM cosmology and are inconsistent with a
flat
matter dominated universe.
The Effect of Substructure on Mass Estimates of Galaxies
Authors:
Brian
M. Yencho, Kathryn
V. Johnston, James
S. Bullock, Katherine
L. Rhode
Comments: 9 pages, 8 figures, Astrophysical Journal, in press
Large galaxies are thought to form hierarchically, from the accretion
and
disruption of many smaller galaxies. Such a scenario should naturally
lead to
galactic phase-space distributions containing some degree of
substructure. We
examine the errors in mass estimates of galaxies and their dark halos
made
using the projected phase-space distribution of a tracer population
(such as a
globular cluster system or planetary nebulae) due to falsely assuming
that the
tracers are distributed randomly. The level of this uncertainty is
assessed by
applying a standard mass estimator to samples drawn from 11 random
realizations
of galaxy halos containing levels of substructure consistent with
current
models of structure formation. We find that substructure will distort
our mass
estimates by up to ~20% - a negligible error compared to statistical
and
measurement errors in current derivations of masses for our own and
other
galaxies. However, this represents a fundamental limit to the accuracy
of any
future mass estimates made under the assumption that the tracer
population is
distributed randomly, regardless of the size of the sample or the
accuracy of
the measurements.
Task Force on Cosmic Microwave Background Research
Authors:
James
Bock (Caltech/JPL), Sarah
Church (Stanford), Mark
Devlin (Penn), Gary
Hinshaw (GSFC), Andrew
Lange (Caltech), Adrian
Lee (Berkeley/LBNL), Lyman
Page (Princeton), Bruce
Partridge (Haverford), John
Ruhl (Case Western), Max
Tegmark (MIT), Peter
Timbie (Wisconsin), Rainer
Weiss (MIT, chair), Bruce
Winstein (Chicago), Matias
Zaldarriaga (Harvard)
Comments: This is the final report of the DoE/NASA/NSF interagency task
force on CMB research chaired by Rai Weiss. 87 pages
One of the most spectacular scientific breakthroughs in past decades
was
using measurements of the fluctuations in the cosmic microwave
background (CMB)
to test precisely our understanding of the history and composition of
the
Universe. This report presents a roadmap for leading CMB research to
its
logical next step, using precision polarization measurements to learn
about
ultra-high-energy physics and the Big Bang itself.
Single Field Inflation models allowed and ruled out by the
three years WMAP data
Authors:
H.
J. de Vega, N.
G. Sanchez
Comments: 29 pages, 24 figures, LaTeX
We study the single field slow-roll inflation models that better fit
the
available CMB and LSS data including the three years WMAP data: new
inflation
and hybrid inflation. We study them as effective field theories in the
Ginsburg-Landau context: a trinomial potential turns out to be a simple
and
well motivated model. The compute the spectral index n_s of the
adiabatic
fluctuations, the ratio r of tensor to scalar fluctuations and the
running
index d n_s/dln k, derive explicit formulae and provide relevant plots.
In new
inflation, and for the three years WMAP central value n_s = 0.95, we
predict
0.03<r<0.04 and -0.00070<d n_s/d ln k<-0.00055. In hybrid
inflation, and for
n_s = 0.95, we predict r = 0.2 and dn_s/dln k=-0.001. We find that r in
new
inflation is a two valued function of n_s in the interval
0.96<n_s<0.9615. In
the first branch we find r<r_{max} = 0.1148.In hybrid inflation we
find a
critical value mu_{0 crit}^2 for the mass parameter mu_0^2 of the field
sigma
coupled to the inflaton.For mu_0^2<Lambda_0 M_{Pl}^2/192, where
Lambda_0 is the
cosmological constant, hybrid inflation is ruled out by the WMAP three
years
data since it yields n_s>1. Hybrid inflation for mu_0^2>Lambda_0
M_{Pl}^2/192
can fullfill all the present CMB+LSS data. Even if chaotic inflation
predicts
n_s values compatible with the data, chaotic inflation is disfavoured
since it
predicts a too high value for the ratio r=0.27. The model which best
fits the
current data and which best prepares the way to the expected data r
< 0.1, is
the trinomial potential with negative mass term: new inflation.
Estimations of baryon asymmetry for different neutrino mass
models
Authors:
Amal
Kr. Sarma, Hijam
Zeen Devi, N.
Nimai Singh
Comments: 14 pages, no figure
We present a comparison of the numerical prediction on baryon asymmetry
of
the Universe in different neutrino mass models. We start with a very
brief
review on the main formalism of baryogenesis via leptogenesis through
decay of
heavy right-handed Majorana neutrinos, and then calculate the baryon
asymmetry
of the universe for known six neutrino mass models viz., three
quasi-degenerate, two inverted and one normal hierarchical models,
which are
derived from canonical seesaw formula. The corresponding mass matrices
for the
right-handed Majorana neutrino as well as the Dirac neutrino, which are
fixed
at the seesaw stage for generating correct light neutrino mass
matrices, are
again employed in the calculation of baryogenesis. This procedure
removes
possible ambiguity on the choices of Dirac neutrino and right-handed
Majorana
mass matrices, and fixes input parameters at the seesaw stage. We find
that the
ranges of predictions from both normal hierarchical model and
degenerate model
(DegT1A) are almost consistent with the observed baryon asymmetry of
the
universe. Combining the present result with other predictions such as
light
neutrino masses and mixing angles, and stability under radiative
corrections in
MSSM, the normal hierarchical model appears to be the most favourable
choice of
nature.
A Universe Without Weak Interactions
Authors:
Roni
Harnik, Graham
D. Kribs, Gilad
Perez
Comments: 27 pages; 4 figures
A universe without weak interactions is constructed that undergoes
big-bang
nucleosynthesis, matter domination, structure formation, and star
formation.
The stars in this universe are able to burn for billions of years,
synthesize
elements up to iron, and undergo supernova explosions, dispersing heavy
elements into the interstellar medium. These definitive claims are
supported by
a detailed analysis where this hypothetical "Weakless Universe" is
matched to
our Universe by simultaneously adjusting Standard Model and
cosmological
parameters. For instance, chemistry and nuclear physics are essentially
unchanged. The apparent habitability of the Weakless Universe suggests
that the
anthropic principle does not determine the scale of electroweak
breaking, or
even require that it be smaller than the Planck scale, so long as
technically
natural parameters may be suitably adjusted. Whether the
multi-parameter
adjustment is realized or probable is dependent on the ultraviolet
completion,
such as the string landscape. Considering a similar analysis for the
cosmological constant, however, we argue that no adjustments of other
parameters are able to allow the cosmological constant to raise up even
remotely close to the Planck scale while obtaining macroscopic
structure. The
fine-tuning problems associated with the electroweak breaking scale and
the
cosmological constant therefore appear to be qualitatively different
from the
perspective of obtaining a habitable universe.
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