1,563 research outputs found
Self-Tuning Dark Energy in Brane World Cosmology
Recently, the self-tuning mechanism of cancellation of vacuum energy has been
proposed in which our universe is a flat 3-brane in a 5-dimensional spacetime.
In this letter, the self-tuning mechanism of dark energy is proposed by
considering the cosmological matter in the brane world. In our model, the bulk
scalar field takes the role of the dark energy and its value is slowly varying
in time. The claim is that even if the enormous amount of vacuum energy exists
on the brane we can adjust the present value of the dark energy to be
consistent with the current observations. In this self-tuning mechanism, the
existence of the constant of integration associated with the bulk scalar is
crucial.Comment: 11pages, LaTe
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
Wavelet analysis of one-dimensional cosmological density fluctuations
Wavelet analysis is proposed as a new tool for studying the large-scale structure formation of the universe. To reveal its usefulness, the wavelet decomposition of one-dimensional cosmological density fluctuations is performed. In contrast with the Fourier analysis, the wavelet analysis has advantage of its ability to keep the information for location of local density peaks in addition to that for their scales. The wavelet decomposition of evolving density fluctuations with various initial conditions is examined. By comparing the wavelet analysis with the usual Fourier analysis, we conclude that the wavelet analysis is promising as the data analysis method for the Sloan Digital Sky Survey and COBE
Braneworld Cosmological Perturbation Theory at Low Energy
Homogeneous cosmology in the braneworld can be studied without solving bulk
equations of motion explicitly. The reason is simply because the symmetry of
the spacetime restricts possible corrections in the 4-dimensional effective
equations of motion. It would be great if we could analyze cosmological
perturbations without solving the bulk. For this purpose, we combine the
geometrical approach and the low energy gradient expansion method to derive the
4-dimensional effective action. Given our effective action, the standard
procedure to obtain the cosmological perturbation theory can be utilized and
the temperature anisotropy of the cosmic background radiation can be computed
without solving the bulk equations of motion explicitly.Comment: 10 pages, Based on a talk presented at ACRGR4, the 4th Australasian
Conference on General Relativity and Gravitation, Monash University,
Melbourne, January 2004. To appear in the proceedings, in General Relativity
and Gravitatio
Hawking Radiation from Fluctuating Black Holes
Classically, black Holes have the rigid event horizon. However, quantum
mechanically, the event horizon of black holes becomes fuzzy due to quantum
fluctuations. We study Hawking radiation of a real scalar field from a
fluctuating black hole. To quantize metric perturbations, we derive the
quadratic action for those in the black hole background. Then, we calculate the
cubic interaction terms in the action for the scalar field. Using these
results, we obtain the spectrum of Hawking radiation in the presence of
interaction between the scalar field and the metric. It turns out that the
spectrum deviates from the Planck spectrum due to quantum fluctuations of the
metric.Comment: 35pages, 4 figure
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