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The Lyman-alpha forest and WMAP year three
Authors: Matteo
Viel, Martin
G. Haehnelt, Antony
Lewis
Comments: 5 pages, 4 figs, 2 tables
A combined analysis of Cosmic Microwave Background
(CMB) and Lyman-a
forest
data allows to constrain the matter power spectrum from small scales of
about 1
Mpc/h all the way to the horizon scale. The long lever arm and
complementarity
provided by such an analysis has previously led to a significant
tightening of
the constraints on the shape and the amplitude of the power spectrum of
primordial density fluctuations. We present here a combined analysis of
the
WMAP three year results with Lyman-a forest data. The amplitude of the
matter
power spectrum sigma_8 and the spectral index ns inferred from the
joint
analysis with high resolution Lyman-a forest data and low resolution
Lyman-a
forest data as analyzed by Viel & Haehnelt (2006) are consistent
with the new
WMAP results to within 1 sigma. The joint analysis with the low
resolution data
as analysed by McDonald et al. (2005) suggest a value of sigma_8 which
is ~ 2
sigma higher than that inferred from the WMAP three year data alone.
The joint
analysis of the three year WMAP and the Lyman-a forest data also does
not
favour a running of the spectral index. The best fit values for a
combined
analysis of the three year WMAP data, other CMB data, 2dF and the \lya
forest
data are (sigma_8, ns) = (0.78\pm 0.03,0.96 \pm 0.01).
osmological parameters from combining the Lyman-alpha forest
with CMB, galaxy clustering and SN constraints
Authors: Uros
Seljak, Anze
Slosar, Patrick
McDonald
Comments: 11 pages, 4 figures
We combine the Ly-alpha forest power spectrum (LYA)
from the Sloan
Digital
Sky Survey (SDSS) and high resolution spectra with the cosmic microwave
background (CMB) including 3-year WMAP, supernovae (SN) and galaxy
clustering
constraints to derive new constraints on cosmological parameters. The
existing
LYA power spectrum analysis is supplemented by constraints on the mean
flux
decrement derived using a principal component analysis for quasar
continua,
which improves the LYA constraints on the linear power. The joint
analysis
reduces the errors on all parameters and prefers the simplest 6
parameter
cosmological model. We find some tension between the WMAP3 and LYA
power
spectrum amplitudes, at the ~2 sigma level, which is partially
alleviated by
the inclusion of other observations: we find sigma_8=0.85+-0.02
compared to
sigma_8=0.80+-0.03 without LYA. For the slope we find n_s=0.965+-0.012.
We find
no evidence for running of the spectral index, dn/dln k=-0.020+-0.012,
in
agreement with inflation. The limits on the sum of neutrino masses are
significantly improved: sum(m_nu)<0.17 eV at 95% (<0.32 eV at
99.9%). This
result, when combined with atmospheric and solar neutrino mixing
constraints,
requires that the neutrino masses cannot be degenerate, m_3/m_1>1.3
(95%).
Assuming a thermalized fourth neutrino we find m_s<0.14 eV at 95%
c.l. and such
neutrino cannot be an explanation for the LSND results. The fit is poor
even in
the limit of massless sterile neutrino since the constraint on the
number of
relativistic neutrino species is N_nu=3.19+0.19-0.15 and N_nu>4 is
excluded at
99.76%. The constraint on the dark energy equation of state is
w=-1.04+-0.06.
The constraint on curvature is Omega_k=-0.003+-0.006. Cosmic strings
limits are
G mu<2.3 10^-7 at 95% c.l.
Improving Cosmological Distance Measurements by
Reconstruction of the Baryon Acoustic Peak
Authors: Daniel
J. Eisenstein, Hee-jong
Seo (Arizona), Edwin
Sirko, David
Spergel (Princeton)
Comments: 5 pages, LaTeX. Submitted to the Astrophysical Journal
The baryon acoustic oscillations are a promising
route to the precision
measure of the cosmological distance scale and hence the measurement of
the
time evolution of dark energy. We show that the non-linear degradation
of the
acoustic signature in the correlations of low-redshift galaxies is a
correctable process. By suitable reconstruction of the linear density
field,
one can sharpen the acoustic peak in the correlation function or,
equivalently,
restore the higher harmonics of the oscillations in the power spectrum.
With
this, one can achieve better measurements of the acoustic scale for a
given
survey volume. Reconstruction is particularly effective at low
redshift, where
the non-linearities are worse but where the dark energy density is
highest. At
z=0.3, we find that one can reduce the sample variance error bar on the
acoustic scale by at least a factor of 2 and in principle by nearly a
factor of
4. We discuss the significant implications our results have for the
design of
galaxy surveys aimed at measuring the distance scale through the
acoustic peak.
On the Robustness of the Acoustic Scale in the Low-Redshift
Clustering of Matter
Authors: Daniel
J. Eisenstein, Hee-jong
Seo (Arizona), Martin
White (UC Berkeley)
Comments: 27 pages, LaTeX. Submitted to the Astrophysical Journal
We discuss the effects of non-linear structure
formation on the
signature of
acoustic oscillations in the late-time galaxy distribution. We argue
that the
dominant non-linear effect is the differential motion of pairs of
tracers
separated by 150 Mpc. These motions are driven by bulk flows and
cluster
formation and are much smaller than the acoustic scale itself. We
present a
model for the non-linear evolution based on the distribution of
pairwise
Lagrangian displacements that provides a quantitative model for the
degradation
of the acoustic signature, even for biased tracers in redshift space.
The
Lagrangian displacement distribution can be calibrated with a
significantly
smaller set of simulations than would be needed to construct a precise
power
spectrum. By connecting the acoustic signature in the Fourier basis
with that
in the configuration basis, we show that the acoustic signature is more
robust
than the usual Fourier-space intuition would suggest because the beat
frequency
between the peaks and troughs of the acoustic oscillations is a very
small
wavenumber that is well inside the linear regime. We argue that any
possible
shift of the acoustic scale is related to infall on 150 Mpc scale,
which is
O(0.5%) fractionally at first-order even at z=0. For the matter, there
is a
first-order cancellation such that the mean shift is O(10^{-4}).
However,
galaxy bias can circumvent this cancellation and produce a sub-percent
systematic bias.
Substructure in lensing clusters and simulations
Authors: Priyamvada
Natarajan (Yale), Gabriella
De Lucia (MPA), Volker
Springel (MPA)
Comments: 16 pages, 9 figures, submitted to MNRAS
We present high-resolution mass reconstructions for
five massive
cluster-lenses spanning a redshift range from $z = 0.18$--0.57
utilising
archival {\it Hubble Space Telescope} ({\it HST}) data and applying
galaxy-galaxy lensing techniques. These detailed mass models were
obtained from
the observations by combining constraints from the strong and weak
lensing
regimes. We ascribe local weak distortions in the shear maps to
perturbations
induced by the presence of galaxy haloes around individual bright
early-type
cluster member galaxies. This technique constrains the mass enclosed
within an
aperture for these subhaloes. We are sensitive to a specific mass range
for
these subhaloes, $10^{11}$ -- $10^{12.5} \msun$, which we associate
with
galaxy-scale subhaloes. Adopting a parametric model for the subhaloes,
we also
derive their velocity dispersion function and the aperture radius
function. The
mass spectrum of substructure in the inner regions of the observed
clusters is
directly compared with that in simulated clusters extracted from the
{\it
Millennium Simulation}. The massfunction, aperture radii and velocity
dispersion function are compared in detail. Overall, we find good
agreement
between the distribution of substructure properties retrieved using the
lensing
analysis and those obtained from the simulation (truncated abstract).
Occam's razor meets WMAP
Authors: Joao
Magueijo, Rafael
D. Sorkin
Using a variety of quantitative implementations of
Occam's razor we
examine
the low quadrupole, the ``axis of evil'' effect and other detections
recently
made appealing to the excellent WMAP data. We find that some razors
{\it fully}
demolish the much lauded claims for departures from scale-invariance.
They all
reduce to pathetic levels the evidence for a low quadrupole (or any
other low
$\ell$ cut-off), both in the first and third year WMAP releases. The
``axis of
evil'' effect is the only anomaly examined here that survives the
humiliations
of Occam's razor, and even then in the category of ``strong'' rather
than
``decisive'' evidence. Statistical considerations aside, differences
between
the various renditions of the datasets remain worrying.
Indication
of a cosmological variation of the proton-electron mass
ratio based on laboratory measurement and reanalysis of H2
spectra
E. Reinhold, R. Buning, U. Hollenstein, A. Ivanchik,
P. Petitjean, W. Ubachs
Based on highly accurate laboratory measurements of Lyman
bands of H2 and an updated representation of the
structure of the ground X 1  and excited B
1 and C
1 u states, a new
set of sensitivity coefficients Ki is derived
for all lines in the H2 spectrum, representing
the dependence of their transition wavelengths on a
possible variation of the proton-electron mass ratio µ=mp/me.
Included are local perturbation effects between B
and C levels and adiabatic corrections. The new
wavelengths and Ki factors are used to compare
with a recent set of highly accurate H2 spectral
lines observed in the Q 0347-383 and Q 0405-443 quasars,
yielding a fractional change in the mass ratio of  µ/µ=(2.4±0.6)×10-5
for a weighted fit and µ/µ=(2.0±0.6)×10-5
for an unweighted fit. This result indicates, at a 3.5 confidence level, that µ could
have decreased in the past 12 Gyr.
Baryon Dynamics, Dark Matter Substructure, and Galaxies
Authors: David
H. Weinberg, Stephane
Colombi, Romeel
Davé, Neal
Katz
Comments: 32 pages including 16 figs. Submitted to ApJ. PDF file with
higher quality versions of Figs 2 and 3 available at this
http URL
By comparing a collisionless cosmological N-body
simulation (DM) to an
SPH
simulation with the same initial conditions, we investigate the
correspondence
between the dark matter subhalos produced by collisionless dynamics and
the
galaxies produced by dissipative gas dynamics in a dark matter
background. When
galaxies in the SPH simulation become satellites in larger groups, they
retain
local dark matter concentrations (SPH subhalos) whose mass is typically
five
times their baryonic mass. The more massive subhalos of the SPH
simulation have
corresponding subhalos of similar mass and position in the DM
simulation; at
lower masses, there is fairly good correspondence, but some DM subhalos
are in
different spatial positions and some suffer tidal stripping or
disruption. The
halo occupation statistics of DM subhalos -- the mean number of
subhalos,
pairs, and triples as a function of host halo mass -- are very similar
to those
of SPH subhalos and SPH galaxies. Gravity of the dissipative baryon
component
amplifies the density contrast of subhalos in the SPH simulation,
making them
more resistant to tidal disruption. Relative to SPH galaxies and SPH
subhalos,
the DM subhalo population is depleted in the densest regions of the
most
massive halos. The good agreement of halo occupation statistics between
the DM
subhalo and SPH galaxy populations leads to good agreement of their
two-point
correlation functions and higher order moments on large scales. The
depletion
of DM subhalos in dense regions depresses their clustering at R<1
Mpc/h. In
these simulations, the "conversation" between dark matter and baryons
is mostly
one-way, with dark matter dynamics telling galaxies where to form and
how to
cluster, but the "back talk" of the baryons influences small scale
clustering
by enhancing the survival of substructure in the densest environments.
Moduli Decays and Gravitinos
Authors: Michael
Dine, Ryuichiro
Kitano, Alexander
Morisse, Yuri
Shirman
Comments: 15 pages
Report-no: SCIPP-2006/05, SLAC-PUB-11805, LA-UR-06-2660
One proposed solution of the moduli problem of string
cosmology
requires that
the moduli are quite heavy, their decays reheating the universe to
temperatures
above the scale of nucleosynthesis. In many of these scenarios, the
moduli are
approximately supersymmetric; it is then crucial that the decays to
gravitinos
are helicity suppressed. In this paper, we discuss situations where
these
decays are, and are not, suppressed. We also comment on a possible
gravitino
problem from inflaton decay.
Gravitinos from Heavy Scalar Decay
Authors: Takehiko
Asaka, Shuntaro
Nakamura, Masahiro
Yamaguchi
Comments: 14 pages, 8 figures
Report-no: TU-768
Cosmological issues of the gravitino production by
the decay of a heavy
scalar field $X$ are examined, assuming that the damped coherent
oscillation of
the scalar once dominates the energy of the universe. The coupling of
the
scalar field to a gravitino pair is estimated both in spontaneous and
explicit
supersymmetry breaking scenarios, with the result that it is
proportional to
the vacuum expectation value of the scalar field in general.
Cosmological
constraints depend on whether the gravitino is stable or not, and we
study each
case separately. For the unstable gravitino with $M_{3/2} \sim$
100GeV--10TeV,
we obtain not only the upper bound, but also the lower bound on the
reheating
temperature after the $X$ decay, in order to retain the success of the
big-bang
nucleosynthesis. It is also shown that it severely constrains the decay
rate
into the gravitino pair. For the stable gravitino, similar but less
stringent
bounds are obtained to escape the overclosure by the gravitinos
produced at the
$X$ decay. The requirement that the free-streaming effect of such
gravitinos
should not suppress the cosmic structures at small scales eliminates
some
regions in the parameter space, but still leaves a new window of the
gravitino
warm dark matter. Implications of these results to inflation models are
discussed. In particular, it is shown that modular inflation will face
serious
cosmological difficulty when the gravitino is unstable, whereas it can
escape
the constraints for the stable gravitino. A similar argument offers a
solution
to the cosmological moduli problem, in which the moduli is relatively
heavy
while the gravitino is light.
A numerical study of non-gaussianity in the curvaton scenario
Authors: Karim
A. Malik, David
H. Lyth
Comments: 14 pages, 9 figures, some in colour
We study the curvaton scenario using gauge-invariant
second order
perturbation theory and solving the governing equations numerically.
Focusing
on large scales we calculate the non-linearity parameter f_nl in the
two-fluid
curvaton model and compare our results with previous analytical studies
employing the sudden decay approximation. We find good agreement of the
two
approaches for large curvaton energy densities at curvaton decay,
Omega_dec,
but significant differences of up to 10 percent for small Omega_dec.
Evidence for a Cosmological Phase Transition From the Dark
Energy Scale
Authors: James
Lindesay
Comments: 42 pages, 9 figures
A finite vacuum energy density implies the existence
of a UV scale for
gravitational modes. This gives a phenomenological scale to the
dynamical
equations governing the cosmological expansion that must satisfy
constraints
consistent with quantum measurability and spatial flatness. Examination
of
these constraints for the observed dark energy density establishes a
time
interval from the transition to the present, suggesting major
modifications
from the thermal equations of state far from Planck density scales. The
assumption that a phase transition initiates the radiation dominated
epoch is
shown under several scenarios to produce fluctuations to the CMB of the
order
observed. Quantum measurability constraints (eg. uncertainly relations)
define
cosmological scales bounded by luminal expansion rates. It is shown
that the
dark energy can consistently be interpreted as being due to the vacuum
energy
of collective gravitational modes which manifest as the zero-point
motions of
coherent Planck scale mass units prior to the UV scale onset of
gravitational
quantum de-coherence for the cosmology.
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