380 research outputs found
Quasi Non-linear Evolution of Stochastic Bias
It is generally believed that the spatial distribution of galaxies does not
trace that of the total mass. The understanding of the bias effect is therefore
necessary to determine the cosmological parameters and the primordial density
fluctuation spectrum from the galaxy survey. The deterministic description of
bias may not be appropriate because of the various stochasticity of galaxy
formation process. In nature, the biasing is epoch dependent and recent deep
survey of the galaxy shows the large biasing at high redshift. Hence, we
investigate quasi non-linear evolution of the stochastic bias by using the tree
level perturbation method. Especially, the influence of the initial cross
correlation on the evolution of the skewness and the bi-spectrum is examined in
detail. We find that the non-linear bias can be generated dynamically. The
small value of the initial cross correlation can bend the \dg-\dm relation
effectively and easily lead to the negative curvature (). We also
propose a method to predict the bias, cross correlation and skewness at high
redshift. As an illustration, the possibility of the large biasing at high
redshift is discussed. Provided the present bias parameter as and
, we predict the large scale bias as at by fitting
the bi-spectrum to the Lick catalog data. Our results will be important for the
future deep sky survey.Comment: 20 pages, 5 Encapsulated Postscript figures, aastex, final version to
appear in Ap
Gravitational Wave Background from Neutrino-Driven Gamma-Ray Bursts
We discuss the gravitational wave background (GWB) from a cosmological
population of gamma-ray bursts (GRBs). Among various emission mechanisms for
the gravitational waves (GWs), we pay a particular attention to the vast
anisotropic neutrino emissions from the accretion disk around the black hole
formed after the so-called failed supernova explosions. The produced GWs by
such mechanism are known as burst with memory, which could dominate over the
low-frequency regime below \sim 10Hz. To estimate their amplitudes, we derive
general analytic formulae for gravitational waveform from the axisymmetric
jets. Based on the formulae, we first quantify the spectrum of GWs from a
single GRB. Then, summing up its cosmological population, we find that the
resultant value of the density parameter becomes roughly \Omega_{GW} \approx
10^{-20} over the wide-band of the low-frequency region, f\sim 10^{-4}-10^1Hz.
The amplitude of GWB is sufficiently smaller than the primordial GWBs
originated from an inflationary epoch and far below the detection limit.Comment: 6 pages, 4 figures, accepted for publication in MNRA
The hydrostatic equilibrium and Tsallis equilibrium for self-gravitating systems
Self-gravitating systems are generally thought to behavior non-extensively
due to the long-range nature of gravitational forces. We obtain a relation
between the nonextensive parameter q of Tsallis statistics, the temperature
gradient and the gravitational potential based on the equation of hydrostatic
equilibrium of self-gravitating systems. It is suggested that the nonextensive
parameter in Tsallis statistics has a clear physical meaning with regard to the
non-isothermal nature of the systems with long-range interactions and Tsallis
equilibrium distribution for the self-gravitating systems describes the
property of hydrostatic equilibrium of the systems.Comment: 7 pages, 9 Reference
A Closure Theory for Non-linear Evolution of Cosmological Power Spectra
We apply a non-linear statistical method in turbulence to the cosmological
perturbation theory and derive a closed set of evolution equations for matter
power spectra. The resultant closure equations consistently recover the
one-loop results of standard perturbation theory and beyond that, it is still
capable of treating the non-linear evolution of matter power spectra. We find
the exact integral expressions for the solutions of closure equations. These
analytic expressions coincide with the renormalized one-loop results presented
by Crocce & Scoccimarro (2006,2007). By constructing the non-linear propagator,
we analytically evaluate the non-linear matter power spectra based on the
first-order Born approximation of the integral expressions and compare it with
those of the renormalized perturbation theory.Comment: 22 pages, 4 figures, accepted for publication in Ap
Solutions of gauge invariant cosmological perturbations in long-wavelength limit
We investigate gauge invariant cosmological perturbations in a spatially flat
Friedman-Robertson-Walker universe with scalar fields. It is well known that
the evolution equation for the gauge invariant quantities has exact solutions
in the long-wavelength limit. We find that these gauge invariant solutions can
be obtained by differentiating the background solution with respect to
parameters contained in the background system. This method is very useful when
we analyze the long-wavelength behavior of cosmological perturbation with
multiple scalar fields.Comment: 17 pages, will appear in Classical and Quantum Gravit
Entropic Upper Bound on Gravitational Binding Energy
We prove that the gravitational binding energy {\Omega} of a self gravitating
system described by a mass density distribution {\rho}(x) admits an upper bound
B[{\rho}(x)] given by a simple function of an appropriate, non-additive
Tsallis' power-law entropic functional Sq evaluated on the density {\rho}. The
density distributions that saturate the entropic bound have the form of
isotropic q-Gaussian distributions. These maximizer distributions correspond to
the Plummer density profile, well known in astrophysics. A heuristic scaling
argument is advanced suggesting that the entropic bound B[{\rho}(x)] is unique,
in the sense that it is unlikely that exhaustive entropic upper bounds not
based on the alluded Sq entropic measure exit. The present findings provide a
new link between the physics of self gravitating systems, on the one hand, and
the statistical formalism associated with non-additive, power-law entropic
measures, on the other hand
Probing anisotropies of gravitational-wave backgroundswith a space-based interferometer II: Perturbative reconstruction of a low-frequency skymap
We present a perturbative reconstruction method to make a skymap of
gravitational-wave backgrounds (GWBs) observed via space-based interferometer.
In the presence of anisotropies in GWBs, the cross-correlated signals of
observed GWBs are inherently time-dependent due to the non-stationarity of the
gravitational-wave detector. Since the cross-correlated signal is obtained
through an all-sky integral of primary signals convolving with the antenna
pattern function of gravitational-wave detectors, the non-stationarity of
cross-correlated signals, together with full knowledge of antenna pattern
functions, can be used to reconstruct an intensity map of the GWBs. Here, we
give two simple methods to reconstruct a skymap of GWBs based on the
perturbative expansion in low-frequency regime. The first one is based on
harmonic-Fourier representation of data streams and the second is based on
"direct" time-series data. The latter method enables us to create a skymap in a
direct manner. The reconstruction technique is demonstrated in the case of the
Galactic gravitational wave background observed via planned space
interferometer, LISA. Although the angular resolution of low-frequency skymap
is rather restricted, the methodology presented here would be helpful in
discriminating the GWBs of galactic origins by those of the extragalactic
and/or cosmological origins.Comment: 23 pages, 12 figures, Phys.Rev.D (2005) in pres
Jeans' gravitational instability and nonextensive kinetic theory
The concept of Jeans gravitational instability is rediscussed in the
framework of nonextensive statistics and its associated kinetic theory. A
simple analytical formula generalizing the Jeans criterion is derived by
assuming that the unperturbed self- gravitating collisionless gas is
kinetically described by the -parameterized class of power law velocity
distributions. It is found that the critical values of wavelength and mass
depend explicitly on the nonextensive -parameter. The standard Jeans
wavelength derived for a Maxwellian distribution is recovered in the limiting
case =1. For power-law distributions with cutoff, the instability condition
is weakened with the system becoming unstable even for wavelengths of the
disturbance smaller than the standard Jeans length .Comment: 5 pages, including 3 figures. Accepted for publication in A&
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