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27 Mar 2006
13 Mar 2006
6 Mar 2006
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Cosmic Reionization Redux
Authors:
Nickolay
Y. Gnedin, Xiaohui
Fan
Comments: Submitted to ApJ. Comments welcome
We show that numerical simulations of reionization that resolve the
Lyman
Limit systems (and, thus, correctly count absorptions of ionizing
photons) have
converged to about 10% level for 5<z<6.2 and are in reasonable
agreement
(within 10%) with the SDSS data in this redshift interval. The SDSS
data thus
constraint the redshift of overlap of cosmic HII regions to z_{OVL} =
6.1+-0.15. At higher redshifts, the simulations are far from
convergence on the
mean Gunn-Peterson optical depth, but achieve good convergence for the
mean
neutral hydrogen fraction. The simulations that fit the SDSS data,
however, do
not have nearly enough resolution to resolve the earliest episodes of
star
formation, and are very far from converging on the precise value of the
optical
depth to Thompson scattering - any value between 6 and 10% is possible,
depending on the convergence rate of the simulations and the fractional
contribution of PopIII stars. This is generally consistent with the
third-year
WMAP results, but much higher resolution simulation are required to
come up
with the sufficiently precise value for the Thompson optical depth that
can be
statistically compared with the WMAP data.
Cross-correlation of WMAP 3rd year and the SDSS DR4 galaxy
survey: new evidence for Dark Energy
Authors:
A.Cabre,
E.Gaztanaga,
M.Manera,
P.Fosalba,
F.Castander
(IEEC/CSIC)
Comments: 5 pages, 5 figures, submitted to MNRAS Letter
We cross-correlate the third-year WMAP data with galaxy samples
extracted
from the SDSS DR4 covering 13% of the sky, increasing by a factor of
3.7 the
volume sampled in previous analyses. The new measurements confirm a
positive
cross-correlation with higher significance (total signal-to-noise of
about
4.7). The correlation as a function of angular scale is well fitted by
the
integrated Sachs-Wolfe (ISW) effect for LCDM flat FRW models with a
cosmological constant (w=-1). The combined analysis of different
samples gives
Omega_L=0.75-0.80 (68% Confidence Level, CL) or 0.70-0.82 (95% CL). We
find
that the best fit Omega_L decreases from 0.82 to 0.75 (95% CL) when we
increase
the median redshift of the galaxy sample from z~0.3 to z~0.5. The quick
drop of
the measured signal with z is too fast for the LCDM cosmology. The data
can be
better reconciled with a model with an effective dark energy equation
of state
w<-1.5. Such phantom cosmology reduces by up to ~20% the amplitude
of the lower
multipoles of the CMB temperature anisotropies with respect the w=-1
prediction, which also brings the models closer to the observations.
Probing Dynamics of Dark Energy with Supernova, Galaxy
Clustering and the Three-Year Wilkinson Microwave Anisotropy Probe
(WMAP) Observations
Authors:
Gong-Bo
Zhao, Jun-Qing
Xia, Bo
Feng, Xinmin
Zhang
Comments: 7 pages, 5 figures Revtex4
Using the Markov chain Monte Carlo (MCMC) method we perform a global
analysis
constraining the dynamics of dark energy in light of the supernova
(Riess
"Gold" samples), galaxy clustering (SDSS 3D power spectra and SDSS
lyman-\alpha
forest information) and the latest three-year Wilkinson Microwave
Anisotropy
Probe (WMAP) observations. We have allowed the dark energy equation of
state to
get across -1 and pay particular attention to the effects when
incorrectly
neglecting dark energy perturbations. We find the parameter space of
dynamical
dark energy is now well constrained and neglecting dark energy
perturbations
will make the parameter space significantly smaller. Dynamical dark
energy
model where the equation of state crosses -1 is mildly favored and the
standard
\LambdaCDM model is still a good fit to the current data.
Towards a Cosmological Hubble Diagram for Type II-P Supernovae
Authors: Peter
Nugent (1), Mark
Sullivan (2), Richard
Ellis (3), Avishay
Gal-Yam (3 and 4), Douglas
C. Leonard (3 and 5), D.
Andrew Howell (2), Pierre
Astier (6), Raymond
G. Carlberg (2), Alex
Conley (2), Sebastien
Fabbro (7), Dominique
Fouchez (8), James
D. Neill (9), Reynald
Pain (6), Kathy
Perrett (2), Chris
J. Pritchet (9), Nicolas
Regnault
(6) ((1) Lawrence Berkeley National Laboratory, (2) University of
Toronto, (3) California Institute of Technology, (4) Hubble
Postdoctoral Fellow, (5) NSF Astronomy and Astrophysics Postdoctoral
Fellow, (6) LPNHE, CNRS-IN2P3 and University of Paris VI & VII, (7)
CENTRA, (8) CPPM, CNRS-IN2P3 and University Aix Marseille II, (9)
University of Victoria)
Comments: 36 pages, 16 figures, accepted for publication in ApJ
We present the first high-redshift Hubble diagram for
Type II-P
supernovae
(SNe II-P) based upon five events at redshift up to z~0.3. This diagram
was
constructed using photometry from the Canada-France-Hawaii Telescope
Supernova
Legacy Survey and absorption line spectroscopy from the Keck
observatory. The
method used to measure distances to these supernovae is based on recent
work by
Hamuy & Pinto (2002) and exploits a correlation between the
absolute brightness
of SNe II-P and the expansion velocities derived from the minimum of
the Fe II
516.9 nm P-Cygni feature observed during the plateau phases. We present
three
refinements to this method which significantly improve the practicality
of
measuring the distances of SNe II-P at cosmologically interesting
redshifts.
These are an extinction correction measurement based on the V-I colors
at day
50, a cross-correlation measurement for the expansion velocity and the
ability
to extrapolate such velocities accurately over almost the entire
plateau phase.
We apply this revised method to our dataset of high-redshift SNe II-P
and find
that the resulting Hubble diagram has a scatter of only 0.26
magnitudes, thus
demonstrating the feasibility of measuring the expansion history, with
present
facilities, using a method independent of that based upon supernovae of
Type
Ia.
On horizons and the cosmic landscape
Authors: George
F R Ellis
Comments: Revised to clarify claims; essential substance unchanged
Susskind claims in his recent book The Cosmic
Landscape that evidence
for the
existence and nature of `pocket universes' in a multiverse would be
available
in the detailed nature of the Cosmic Blackbody Background Radiation
that
constantly bathes all parts of our observable universe. I point out
that
acceptance of the complex chain of argument involved does not imply
possible
experimental verification of multiverses at the present time. Rather
this claim
relates only to theoretically possible observations in the very far
future of
the universe.
How to find a dark matter sterile neutrino?
Authors:
A.
Boyarsky, A.
Neronov, O.
Ruchayskiy, M.
Shaposhnikov, I.
Tkachev
Comments: 5 pp, revtex
We propose a strategy of how to look for dark matter (DM) particles
possessing a radiative decay channel and derive constraints on their
parameters
from observations of X-rays from our own Galaxy and its dwarf
satellites. When
applied to the sterile neutrinos in keV mass range, it allows a
significant
improvement of restrictions to its parameters, as compared with
previous works.
Inflating in a Better Racetrack
Authors: J.J.
Blanco-Pillado, C.P.
Burgess, J.M.
Cline, C.
Escoda, M.
Gomez-Reino, R.
Kallosh, A.
Linde, F.
Quevedo
Comments: 20 pages, 6 figures
Report-no: DAMTP-2006-20, SU-ITP-06-07
We present a new version of our racetrack inflation
scenario which,
unlike
our original proposal, is based on an explicit compactification of type
IIB
string theory: the Calabi-Yau manifold P^4_[1,1,1,6,9]. The
axion-dilaton and
all complex structure moduli are stabilized by fluxes. The remaining 2
Kahler
moduli are stabilized by a nonperturbative superpotential, which has
been
explicitly computed. For this model we identify situations for which a
linear
combination of the axionic parts of the two Kahler moduli acts as an
inflaton.
As in our previous scenario, inflation begins at a saddle point of the
scalar
potential and proceeds as an eternal topological inflation. For a
certain range
of inflationary parameters, we obtain the COBE-normalized spectrum of
metric
perturbations and an inflationary scale of M = 3 x 10^{14} GeV. We
discuss
possible changes of parameters of our model and argue that anthropic
considerations favor those parameters that lead to a nearly flat
spectrum of
inflationary perturbations, which in our case is characterized by the
spectral
index n_s = 0.95.
Testing Gaussian random hypothesis with the cosmic microwave
background temperature anisotropies in the three-year WMAP data
Authors:
Lung-Yih
Chiang (1), Pavel
D. Naselsky (1), Peter
Coles (2) ((1) Niels Bohr Institute, (2) Nottingham University)
Comments: submitted to ApJL, some corrections on the curves of Fig.5
and 6. The curves and extrema locations are shifted by 180 degs, but
the statistics are unchanged
We test the hypothesis that the temperature of the cosmic microwave
background is consistent with a Gaussian random field defined on the
celestial
sphere, using de-biased internal linear combination (DILC) map produced
from
the 3-year WMAP data. We test the phases for spherical harmonic modes
with l <=
10 (which should be the cleanest) for their uniformity, randomness, and
correlation with those of the foreground templates. The phases
themselves are
consistent with a uniform distribution, but not for l <= 5, and the
differences
between phases are not consistent with uniformity. For l=3 and l=6, the
phases
of the CMB maps cross-correlate with the foregrounds, suggestion the
presence
of residual contamination in the DLC map even on these large scales. We
also
use a one-dimensional Fourier representation to assemble a_lm into the
\Delta
T_l(\phi) for each l mode, and test the positions of the resulting
maxima and
minima for consistency with uniformity randomness on the unit circle.
The
results show significant departures at the 0.5% level, with the
one-dimensional
peaks being concentrated around \phi=180 degs. This strongly
significant
alignment with the Galactic meridian, together with the
cross-correlation of
DILC phases with the foreground maps, strongly suggests that even the
lowest
spherical harmonic modes in the map are significantly contaminated with
foreground radiation.
Non-Gaussianities in two-field inflation
Authors:
Filippo
Vernizzi, David
Wands
Comments: 28 pages, 6 figures
We study the bispectrum of the curvature perturbation on uniform energy
density hypersurfaces in models of inflation with two scalar fields
evolving
simultaneously. In the case of a separable potential, it is possible to
compute
the curvature perturbation up to second order in the perturbations,
generated
on large scales due to the presence of non-adiabatic perturbations, by
employing the $\delta N$-formalism, in the slow-roll approximation. In
this
case, we provide an analytic formula for the nonlinear parameter
$f_{NL}$. We
apply this formula to double inflation with two massive fields, showing
that it
does not generate significant non-Gaussianity during inflation; the
nonlinear
parameter at the end of inflation is slow-roll suppressed. Finally, we
develop
a numerical method for generic two-field models of inflation, which
allows us
to go beyond the slow-roll approximation and confirms our analytic
results for
double inflation.
Identifying the curvaton within MSSM
Authors:
Rouzbeh
Allahverdi, Kari
Enqvist, Asko
Jokinen, Anupam
Mazumdar
Comments: 9 pages
We consider inflaton couplings to MSSM flat directions and the
thermalization
of the inflaton decay products, taking into account gauge symmetry
breaking due
to flat direction condensates. We then search for a suitable curvaton
candidate
among the flat directions, requiring an early thermally induced start
for the
flat direction oscillations to facilitate the necessary curvaton energy
density
dominance. We demonstrate that the supersymmetry breaking $A$-term is
crucial
for achieving a successful curvaton scenario. Among the many possible
candidates, we identify the ${\bf u_1dd}$ flat direction as a viable
MSSM
curvaton.
Higgs Sector in Extensions of the MSSM
Authors:
Vernon
Barger, Paul
Langacker, Hye-Sung
Lee, Gabe
Shaughnessy
Comments: 64 pages, 15 figures
Extensions of the Minimal Supersymmetric Standard Model (MSSM) with
additional singlet scalar fields solve the important mu-parameter fine
tuning
problem of the MSSM. We compute and compare the neutral Higgs boson
mass
spectra, including one-loop corrections, of the following MSSM
extensions:
Next-to-Minimal Supersymmetric Standard Model (NMSSM), the
nearly-Minimal
Supersymmetric Standard Model (nMSSM), and the U(1)'-extended Minimal
Supersymmetric Standard Model (UMSSM) by performing scans over model
parameters. We find that the Secluded U(1)'-extended Minimal
Supersymmetric
Standard Model (sMSSM) is identical to the nMSSM if three of the
additional
scalars decouple. The dominant part of the one-loop corrections are
model-independent since the singlet field does not couple to MSSM
particles
other than the Higgs doublets. Thus, model-dependent parameters enter
the
masses only at tree-level. We apply constraints from LEP bounds on the
Standard
Model and MSSM Higgs boson masses and the MSSM chargino mass, the
invisible Z
decay width, and the Z-Z' mixing angle. Some extended models permit a
Higgs
boson with mass substantially below the SM LEP limit or above
theoretical
limits in the MSSM. Ways to differentiate the models via masses,
couplings,
decays and production of the Higgs bosons are discussed.
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