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Cosmology and the Bispectrum
Authors: Emiliano
Sefusatti, Martin
Crocce, Sebastian
Pueblas, Roman
Scoccimarro
Comments: 22 pages, 12 figures
Report-no: FERMILAB-PUB-06-083-A
The present spatial distribution of galaxies in the
Universe is
non-Gaussian,
with 40% skewness in 50 Mpc/h spheres, and remarkably little is known
about the
information encoded in it about cosmological parameters beyond the
power
spectrum. In this work we present an attempt to bridge this gap by
studying the
bispectrum, paying particular attention to a joint analysis with the
power
spectrum and their combination with CMB data. We address the covariance
properties of the power spectrum and bispectrum including the effects
of beat
coupling that lead to interesting cross-correlations, and discuss how
baryon
acoustic oscillations break degeneracies. We show that the bispectrum
has
significant information on cosmological parameters well beyond its
power in
constraining galaxy bias, and when combined with the power spectrum is
more
complementary than combining power spectra of different samples of
galaxies,
since non-Gaussianity provides a somewhat different direction in
parameter
space. In the framework of flat cosmological models we show that most
of the
improvement of adding bispectrum information corresponds to parameters
related
to the amplitude and effective spectral index of perturbations, which
can be
improved by almost a factor of two. Moreover, we demonstrate that the
expected
statistical uncertainties in sigma8 of a few percent are robust to
relaxing the
dark energy beyond a cosmological constant.
On the Growth of Perturbations as a Test of Dark Energy
Authors: Edmund
Bertschinger
Comments: 16 pages, 1 figure, submitted to ApJ
The strongest evidence for dark energy comes
presently from geometric
techniques such as the supernova distance-redshift relation. By
combining the
measured expansion history with the Friedmann equation one determines
the
energy density and its time evolution, hence the equation of state of
dark
energy. Because these methods rely on the Friedmann equation which has
not been
independently tested it is desirable to find alternative methods that
work for
both general relativity and other theories of gravity.
Assuming that sufficiently large patches of a perturbed
Robertson-Walker
spacetime evolve like separate Robertson-Walker universes and that
shear stress
is unimportant on large scales, we reduce the long-wavelength metric,
density,
and velocity potential perturbations to quadratures. The general
solution is
given including curvature perturbations, entropy perturbations (whose
evolution
generally requires solving additional equations of motion), and nonzero
background curvature for any theory of gravity permitting a
Robertson-Walker
solution. When combined with the expansion history measured
geometrically, the
long-wavelength solution provide a test that may distinguish modified
gravity
from other explanations of dark energy. Alternative cosmological-scale
tests of
gravity are proposed in terms of the constraint equations of general
relativity.
How astrophysical neutrino sources could be used for early
measurements of neutrino mass hierarchy and leptonic CP phase
Authors: Walter
Winter
Comments: 30 pages, 15 figures
We discuss the possible impact of astrophysical
neutrino flux
measurements at
neutrino telescopes on the neutrino oscillation program of reactor
experiments
and neutrino beams. We consider neutrino fluxes from neutron sources,
muon
damped sources, and pion sources, where we parameterize the input from
these
sources in terms of the flux ratio $R=\phi_\mu/(\phi_e+\phi_\tau)$
which can be
extracted from the muon track to shower ratio in a neutrino telescope.
While it
is difficult to obtain any information from this ratio alone, we
demonstrate
that the dependence on the oscillation parameters is very complementary
to the
one of reactor experiments and neutrino beams. We find that for large
values of
$\sin^2 2 \theta_{13}$, a measurement of R with a precision of about
20% or
better may not only improve the measurement of the leptonic CP phase,
but also
help the determination of the mass hierarchy. In some cases, early
information
on $\delta_{CP}$ may even be obtained from Double Chooz and an
astrophysical
flux alone without the help of superbeams. For small values of $\sin^2
2
\theta_{13}$, we find that using the information from an astrophysical
neutrino
flux could eliminate the octant degeneracy better than reactor
experiments and
beams alone. Finally, we demonstrate that implementing an additional
observable
based on the electromagnetic to hadronic shower ratio at a neutrino
telescope
(such as at higher energies) could be especially beneficial for pion
beam
sources.
Minimal Noncanonical Cosmologies
Authors:
Gabriela
Barenboim, Joseph
D. Lykken
Comments: 20 pages, 5 figures, 3 tables
Report-no: FERMILAB-Pub-06/066-T, FTUV-06/0329
We demonstrate how much it is possible to deviate from the standard
cosmological paradigm of inflation-assisted LambdaCDM, keeping within
current
observational constraints, and without adding to or modifying any
theoretical
assumptions. We show that within a minimal framework there are many new
possibilities, some of them wildly different from the standard picture.
We
present three illustrative examples of new models, described
phenomenologically
by a noncanonical scalar field coupled to radiation and matter. These
models
have interesting implications for inflation, quintessence, reheating,
electroweak baryogenesis, and the relic densities of WIMPs and other
exotics.
Where are the z=4 Lyman Break Galaxies? Results from
Conditional Luminosity Function Models of Luminosity-dependent
Correlation Functions
Authors: Asantha
Cooray (Irvine), Masami
Ouchi (STSCI)
Comments: 13 pages, 9 figures; accepted for publication in Mon. Not.
Roy. Astron. Soc.; low resolution figures submitted here. A pdf file
with high resolution figures available at this http URL
Using the conditional luminosity function (CLF) --
the luminosity
distribution of galaxies in a dark matter halo -- as a way to model
galaxy
statistics, we study how z=4 Lyman Break Galaxies (LBGs) are
distributed in
dark matter halos. For this purpose, we measure luminosity-dependent
clustering
of LBGs in the Subaru/XMM-Newton Deep Field by separating a sample of
16,920
galaxies to three magnitude bins in i'-band between 24.5 and 27.5. Our
models
fits to data show a possible trend for more luminous galaxies to appear
as
satellites in more massive halos. The satellite fraction of galaxies at
z=4 in
these magnitude bins is 0.13 to 0.3, 0.09 to 0.22, and 0.03 to 0.14,
respectively, where the 1 sigma ranges account for differences coming
from two
different estimates of the z=4 LF from the literature. To jointly
explain the
LF and the large-scale linear bias factor of z=4 LBGs as a function of
rest-UV
luminosity requires central galaxies to be brighter in UV at z =4 than
present-day galaxies in same dark matter mass halos. Moreover, UV
luminosity of
central galaxies in halos with total mass greater than roughly 10^{12}
M_sun
must decrease from z=4 to today by an amount more than the luminosity
change
for galaxies in halos below this mass. This mass-dependent luminosity
evolution
is preferred at more than 3 sigma confidence level compared to a
pure-luminosity evolution scenario where all galaxies decrease in
luminosity by
the same amount from z=4 to today. The scenario preferred by the data
is
consistent with the ``down-sizing'' picture of galaxy evolution.
The large-scale structure of the Universe
Authors: Volker
Springel (MPA), Carlos
S. Frenk (Durham), Simon
D. M. White (MPA)
Comments: Invited review to Nature (27 April 2006 issue), Early
Universe Supplement, 34 pages, 6 figures (partially size reduced)
Journal-ref: Nature, 2006, 440, 1137
Research over the past 25 years has led to the view
that the rich
tapestry of
present-day cosmic structure arose during the first instants of
creation, where
weak ripples were imposed on the otherwise uniform and rapidly
expanding
primordial soup. Over 14 billion years of evolution, these ripples have
been
amplified to enormous proportions by gravitational forces, producing
ever-growing concentrations of dark matter in which ordinary gases
cool,
condense and fragment to make galaxies. This process can be faithfully
mimicked
in large computer simulations, and tested by a variety of observations
that
probe the history of the Universe starting from just 400,000 yr after
the Big
Bang.
Gravitational lensing of distant gamma-ray bursts mimics
evolving dark energy
Authors: Masamune
Oguri, Keitaro
Takahashi (Princeton)
Comments: 4 pages, 3 figures
Gamma-Ray Bursts (GRBs) offer a potentially powerful
way to extend the
Hubble
diagram to very high redshifts and to constrain the nature of dark
energy in a
way complementary to distant type Ia supernovae. We show that its usage
as a
cosmological probe is limited by gravitational lensing. In addition to
increasing the dispersions of distance measurements, lensing
systematically
brightens distant GRBs through the magnification bias, which mimics
evolving
dark energy in the Hubble diagram. We perform Monte-Carlo simulations
of GRBs
assuming a cosmological constant dominated universe and then constrain
the dark
energy equation of state neglecting gravitational lens effects. We find
that
the originally assumed model is rejected by 68% confidence limit when
the
dispersion of inferred luminosities is comparable to that of type Ia
supernovae. The precise degree of the bias in cosmological parameter
determinations depends strongly on the shape of the luminosity function
of
GRBs, implying that the deconvolution of gravitational lensing effects
is quite
challenging.
Supergravity Modification of D-term Hybrid Inflation: Solving
the Cosmic String and Spectral Index Problems via a Right-Handed
Sneutrino
Authors: Chia-Min
Lin, John
McDonald
Comments: 14 pages LaTeX, 2 eps figures
Supergravity corrections due to the energy density of
a right-handed
sneutrino can generate a negative mass squared for the inflaton,
flattening the
inflaton potential and reducing the spectral index and inflaton energy
density.
For the case of D-term hybrid inflation, we show that the spectral
index can be
lowered from the conventional value n = 0.98 to a value within the
range
allowed by the latest WMAP analysis, n = 0.951^{+0.015}_{-0.019}. The
modified
energy density is consistent with non-observation of cosmic strings in
the CMB
if n < 0.946. The WMAP lower bound on the spectral index implies
that the
D-term cosmic string contribution may be very close present CMB limits,
contributing at least 5% to the CMB multipoles.
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.
The $\nu$MSM, Inflation, and Dark Matter
Authors: Mikhail
Shaposhnikov, Igor
Tkachev
Comments: 9 pages
Report-no: CERN-PH-TH/2006-069
We show how to enlarge the $\nu$MSM (the minimal
extension of the
standard
model by three right-handed neutrinos) to incorporate inflation and
provide a
common source for electroweak symmetry breaking and for right-handed
neutrino
masses. In addition to inflation, the resulting theory can explain
simultaneously dark matter and the baryon asymmetry of the Universe; it
is
consistent with experiments on neutrino oscillations and with all
astrophysical
and cosmological constraints on sterile neutrino as a dark matter
candidate.
The mass of inflaton can be much smaller than the electroweak scale.
Supersymmetric Hybrid Inflation with Non-Minimal Kahler
potential
Authors: M.
Bastero-Gil, S.
F. King, Q.
Shafi
Comments: 14 pages, 5 figures; footnote and reference added
Report-no: BA-06-14, CERN-PH-TH/2006-071, UG-FT/204/06, CAFPE/74/06
Minimal supersymmetric hybrid inflation based on a
minimal Kahler
potential
predicts a spectral index n_s\gsim 0.98. On the other hand, WMAP three
year
data prefers a central value n_s \approx 0.95. We propose a class of
supersymmetric hybrid inflation models based on the same minimal
superpotential
but with a non-minimal Kahler potential. Including radiative
corrections using
the one-loop effective potential, we show that the prediction for the
spectral
index is sensitive to the small non-minimal corrections, and can lead
to a
significantly red-tilted spectrum, in agreement with WMAP.
Curvature perturbation from symmetry breaking the end of
inflation
Authors: Laila
Alabidi, David
Lyth
Comments: 4 pages, 2 figures
We consider a two-field hybrid inflation model, in
which the curvature
perturbation is predominantly generated at the end of inflation. We
find that
we can get a measurable amount of non-gaussianity for certain couplings
of the
fields to the waterfall.
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