http://staff.ustc.edu.cn/~wzhao7/c_index_files/main.files/lss.pdf

Large scale structure of the universe and cosmological perturbation theory

In the current paradigm there is a non-trivial bias expected in the process of galaxy formation. Thus, the observed statistical properties of the galaxy distribution do not necessarily extend to the underlying matter distribution. Gravitational evolution of initially Gaussian seed fluctuations predicts that the connected moments of the matter fluctuations exhibit a hierarchical structure, at least in the limit of small dispersion. This same hierarchical structure has been found in the galaxy distribution, but it is not clear to what extent it reflects properties of the matter distribution or properties of a galaxy formation bias. In this paper we consider the consequences of an arbitrary, effectively local biasing transformation of a hierarchical underlying matter distribution. We show that a general form of such a transformation preserves the hierarchical properties and the shape of the dispersion in the limit of small fluctuations, i.e. on large scales, although the values of the

Biasing and Hierarchical Statistics in Large-scale Structure

The nature of the fuel that drives today's cosmic acceleration is an open and tantalizing mystery. We entertain the suggestion that the acceleration is not the manifestation of yet another new ingredient in the cosmic gas tank, but rather a signal of our first real lack of understanding of gravitational physics. By requiring that the underlying gravity theory respect Birkhoff's law, we derive the modified gravitational force law necessary to generate any given cosmology, without reference to the fundamental theory, revealing modifications of gravity at scales typically much smaller than today's horizon. We discuss how, through these modifications, the growth of density perturbations, the late-time integrated Sachs-Wolfe effect, and even solar-system measurements may be sensitive to whether today's cosmic acceleration is generated by dark energy or modified gravitational dynamics, and are subject to imminent observational discrimination. We argue how these conclusions can be more generic, and probably not dependent on the validity of Birkhoff's law.

https://arxiv.org/pdf/astro-ph/0307034.pdf

Differentiating between modified gravity and dark energy

In this work we investigate the possibility of having a late time accelerated phase of the universe, suggested by recent supernova observation, in the context of Brans-Dicke theory with a potential having a time dependent mass squared term which has recently become negative and a matter field. We find that while a perfect fluid (pressureless and with pressure) cannot support this acceleration, a fluid with dissipative pressure can drive this late time acceleration for a simple power-law expansion of the universe. We have also calculated some cosmological parameters in our model to match with observations.

Late time acceleration in Brans-Dicke cosmology

The nature of the fuel that drives today’s cosmic acceleration is an open and tantalizing mystery. We entertain the suggestion that the acceleration is not the manifestation of yet another new ingredient in the cosmic gas tank, but rather a signal of our first real lack of understanding of gravitational physics. By requiring that the underlying gravity theory respects Birkhoff’s law, we derive the modified gravitational force-law necessary to generate any given cosmology, without reference to the fundamental theory, revealing modifications of gravity at scales typically much smaller than today’s horizon. We discuss how through these modifications, the growth of density perturbations, the late-time integrated Sachs–Wolfe effect, and even solar-system measurements may be sensitive to whether today’s cosmic acceleration is generated by dark energy or modified gravitational dynamics, and are subject to imminent observational discrimination. We argue how these conclusions can be more generic, and probably not dependent on the validity of Birkhoff’s law. E-mail: lue@bifur.cwru.edu E-mail: rs123@nyu.edu E-mail: starkman@balin.cwru.edu

Differentiating between Modified Gravity and Dark Energy

We reconsider the problem of gravitational structure formation inside and outside general relativity (GR), in both the weakly and strongly nonlinear regime We show how these regimes can be explored observationally through clustering of high-order cumulants and through the epoch of formation, abundance, and clustering of collapse structures, using Press-Schechter formalism and its extensions We address the question of how different these predictions are when using a nonstandard theory of gravity We study examples of cosmologies that do not necessarily obey Einstein's field equations: scalar-tensor theories (STT), such as Brans-Dicke (BD), parametrized with ω, a nonstandard parameterization of the Hubble law, H2 = a-3(1+), or a nonstandard cosmic equation of state p = γρ, where γ can be chosen irrespective of the cosmological parameters (ΩM and ΩΛ) We present some preliminary bounds on γ, ω, and from observations of the skewness and kurtosis in the Automated Plate Measuring (APM) Galaxy Survey This test is independent of the overall normalization of rms fluctuations We also show how abundances and formation times change under these assumptions Upcoming data on nonlinear growth will place strong constraints on such variations from the standard paradigm

Nonlinear Gravitational Growth of Large-Scale Structures Inside and Outside Standard Cosmology

We reconsider the problem of nonlinear structure formation inside and outside General Relativity (GR), both in the weakly and strongly nonlinear regime. We show how these regimes can be explored observationally through clustering of high-order cumulants and through the epoch of formation, abundance and clustering of collapse structures, using Press and Schechter (1974, Astrophys. J. 187: 425-438) formalism and its extensions.

J. A. Lobo

Papers

Nonlinear Gravitational Growth of Large-Scale Structures Inside and Outside Standard Cosmology

Nonlinear Gravitational Growth Inside and Outside the Standard Cosmology