1,888 research outputs found
Galaxy Bias and Halo-Occupation Numbers from Large-Scale Clustering
We show that current surveys have at least as much signal to noise in
higher-order statistics as in the power spectrum at weakly nonlinear scales. We
discuss how one can use this information to determine the mean of the galaxy
halo occupation distribution (HOD) using only large-scale information, through
galaxy bias parameters determined from the galaxy bispectrum and trispectrum.
After introducing an averaged, reasonably fast to evaluate, trispectrum
estimator, we show that the expected errors on linear and quadratic bias
parameters can be reduced by at least 20-40%. Also, the inclusion of the
trispectrum information, which is sensitive to "three-dimensionality" of
structures, helps significantly in constraining the mass dependence of the HOD
mean. Our approach depends only on adequate modeling of the abundance and
large-scale clustering of halos and thus is independent of details of how
galaxies are distributed within halos. This provides a consistency check on the
traditional approach of using two-point statistics down to small scales, which
necessarily makes more assumptions. We present a detailed forecast of how well
our approach can be carried out in the case of the SDSS.Comment: 16 pages, 9 figure
Dynamics of a Dark Matter Field with a Quartic Self-Interaction Potential
It may prove useful in cosmology to understand the behavior of the energy
distribution in a scalar field that interacts only with gravity and with itself
by a pure quartic potential, because if such a field existed it would be
gravitationally produced, as a squeezed state, during inflation. It is known
that the mean energy density in such a field after inflation varies with the
expansion of the universe in the same way as radiation. I show that if the
field initially is close to homogeneous, with small energy density contrast
delta rho /rho and coherence length L, the energy density fluctuations behave
like acoustic oscillations in an ideal relativistic fluid for a time on the
order of L/|delta rho /rho|. This ends with the appearance of features that
resemble shock waves, but interact in a close to elastic way that reversibly
disturbs the energy distribution.Comment: 7 pages, 5 figures, submitted to Phys Rev
Infrared divergence of pure Einstein gravity contributions to cosmological density power spectrum
We probe the pure Einstein's gravity contributions to the second-order
density power spectrum. In the small-scale, we discover that the Einstein's
gravity contribution is negligibly small. This guarantees that Newton's gravity
is sufficient to handle the baryon acoustic oscillation scale. In the large
scale, however, we discover that the Einstein's gravity contribution to the
second-order power spectrum dominates the linear-order power spectrum. Thus,
pure Einstein gravity contribution appearing in the third-order perturbation
leads to an infrared divergence in the power spectrum.Comment: Changed contents, to appear in Physical Review Letter
Primordial fractal density perturbations and structure formation in the Universe: 1-Dimensional collisionless sheet model
Two-point correlation function of galaxy distribution shows that the
structure in the present Universe is scale-free up to a certain scale (at least
several tens Mpc), which suggests that a fractal structure may exist. If small
primordial density fluctuations have a fractal structure, the present
fractal-like nonlinear structure below the horizon scale could be naturally
explained. We analyze the time evolution of fractal density perturbations in
Einstein-de Sitter universe, and study how the perturbation evolves and what
kind of nonlinear structure will come out. We assume a one-dimensional
collisionless sheet model with initial Cantor-type fractal perturbations. The
nonlinear structure seems to approach some attractor with a unique fractal
dimension, which is independent of the fractal dimensions of initial
perturbations. A discrete self-similarity in the phase space is also found when
the universal nonlinear fractal structure is reached.Comment: 17 pages, 19 jpeg figures. Accepted for publication in ApJ. Figures
are also available from
http://www.phys.waseda.ac.jp/gravity/~tatekawa/0003124/figs.tar.g
RMS Radio Source Contributions to the Microwave Sky
Cross-correlations of the WMAP full sky K, Ka, Q, V, and W band maps with the
1.4 GHz NVSS source count map and the HEAO I A2 2-10 keV full sky X-ray flux
map are used to constrain rms fluctuations due to unresolved microwave sources
in the WMAP frequency range. In the Q band (40.7 GHz), a lower limit, taking
account of only those fluctuations correlated with the 1.4 GHz radio source
counts and X-ray flux, corresponds to an rms Rayleigh-Jeans temperature of ~ 2
microKelvin for a solid angle of one square degree. The correlated fluctuations
at the other bands are consistent with a beta = -2.1 +- 0.4 frequency spectrum.
Using the rms fluctuations of the X-ray flux and radio source counts, and the
cross-correlation of these two quantities as a guide, the above lower limit
leads to a plausible estimate of ~ 5 microKelvin for Q-band rms fluctuations in
one square degree. This value is similar to that implied by the excess, small
angular scale fluctuations observed in the Q band by WMAP, and is consistent
with estimates made by extrapolating low-frquency source counts.Comment: 17 pages, 8 figures, submitted to Ap
Particle linear theory on a self-gravitating perturbed cubic Bravais lattice
Discreteness effects are a source of uncontrolled systematic errors of N-body
simulations, which are used to compute the evolution of a self-gravitating
fluid. We have already developed the so-called "Particle Linear Theory" (PLT),
which describes the evolution of the position of self-gravitating particles
located on a perturbed simple cubic lattice. It is the discrete analogue of the
well-known (Lagrangian) linear theory of a self-gravitating fluid. Comparing
both theories permits to quantify precisely discreteness effects in the linear
regime. It is useful to develop the PLT also for other perturbed lattices
because they represent different discretizations of the same continuous system.
In this paper we detail how to implement the PLT for perturbed cubic Bravais
lattices (simple, body and face-centered) in a cubic simulation box. As an
application, we will study the discreteness effects -- in the linear regime --
of N-body simulations for which initial conditions have been set-up using these
different lattices.Comment: 9 pages, 4 figures and 4 tables. Minor corrections to match published
versio
Dynamics of gas bubbles in an oscillating pressure field Annual report, Jul. 1965 - Aug. 1966
Gas bubble dynamics in oscillating pressure fiel
Nonlinear cosmological power spectra in Einstein's gravity
Is Newton's gravity sufficient to handle the weakly nonlinear evolution
stages of the cosmic large-scale structures? Here we resolve the issue by
analytically deriving the density and velocity power spectra to the second
order in the context of Einstein's gravity. The recently found pure general
relativistic corrections appearing in the third-order perturbation contribute
to power spectra to the second order. In this work the complete density and
velocity power spectra to the second order are derived. The power transfers
among different scales in the density power spectrum are estimated in the
context of Einstein's gravity. The relativistic corrections in the density
power spectrum are estimated to be smaller than the Newtonian one to the second
order, but these could be larger than higher-order nonlinear Newtonian terms.Comment: to appear in Phys. Rev. D, 6 pages, no figur
Propagators in Lagrangian space
It has been found recently that propagators, e.g. the cross-correlation
spectra of the cosmic fields with the initial density field, decay
exponentially at large-k in an Eulerian description of the dynamics. We explore
here similar quantities defined for a Lagrangian space description. We find
that propagators in Lagrangian space do not exhibit the same properties: they
are found not to be monotonic functions of time, and to track back the linear
growth rate at late time (but with a renormalized amplitude). These results
have been obtained with a novel method which we describe alongside. It allows
the formal resummation of the same set of diagrams as those that led to the
known results in Eulerian space. We provide a tentative explanation for the
marked differences seen between the Eulerian and the Lagrangian cases, and we
point out the role played by the vorticity degrees of freedom that are specific
to the Lagrangian formalism. This provides us with new insights into the
late-time behavior of the propagators.Comment: 14 pages, 5 figure
Hierarchical clustering and formation of power-law correlation in 1-dimensional self-gravitating system
The process of formation of fractal structure in one-dimensional
self-gravitating system is examined numerically. It is clarified that
structures created in small spatial scale grow up to larger scale through
clustering of clusters, and form power-law correlation.Comment: 9pages,4figure
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