Modified Gravity Progresses And Outlook Of Theories Numerical Techniques And Observational Tests

Modified gravity theories have been a main focus of theoretical cosmology research in the past decade or so, and have been quickly developing into a mature research field that attracts attention, interest and effort from both theoretical and observational cosmologists. To be prepared for fully exploiting the future observational data, and to provide a guidance for people who are new to this field, it is useful to have a comprehensive review to summarise the current state of knowledge and to foresee the future developments.This book presents expert reviews on different topics in the field, which are then coordinated and organised in a self-consistent and self-contained manner. It is suitable for graduate students and researchers interested in the frontier research of gravity theories.

'The book concentrates attention on extended alternative theories of gravity and on the best astrophysical laboratories to probe the strong gravity-field regime: black holes, pulsars and neutron stars … Readers will likely share the satisfaction the editor and contributors say they experienced as they organized the book.'SirReadaLotFor more than a century, our understanding of gravitational physics was based on Albert Einstein's theory of General Relativity, which fundamentally changed our understanding of the Universe, its origin, and its evolutionary process. General Relativity accurately describes a large number of phenomena on very different scales. As such, it has been very well tested and its remarkable predictions are compatible with most experimental and observational data. However, the observational and experimental results compatible with General Relativity fall in its vast majority under the weak gravitational field regime. In recent years, discrepancies between the data and the corresponding predictions of General Relativity have been observed and have generated intense research activity. One of the most critical aspects of General Relativity is the presence of singularities in extreme physical situations. These discrepancies indicate that either the parameters of the theory must be modified in the regime of strong field gravity/high energy and large space-time curvature, or the theory itself should be modified. In this book, we focus our attention on extended alternative gravity theories and the best astrophysical laboratories to probe the strong field regime: black holes, pulsars, and neutron stars.

This book is devoted to researchers who would like to investigate interactions among gravitational waves and matter fields beyond linear order, including the phenomena of memory effects, gravitational Faraday rotation, soft theorems, and formations of spacetime singularities due to the mutual focus of gravitational waves. Readers only require a basic understanding of general relativity to understand the materials.The book starts with an overview on the fundamentals of the Newman-Penrose formalism and a brief introduction to distribution theory, with which the author systematically develops a mathematical description of spacetimes of colliding plane waves. Then, the author presents a frame-independent definition of polarization of a plane gravitational wave in a curved spacetime, studies in detail the gravitational Faraday rotation of two plane gravitational waves, and shows that each of them can serve as a medium to the other precisely due to their nonlinear interactions. Exact solutions are also presented, which represent a variety of models including the collisions of two plane gravitational waves and the collisions of a plane gravitational wave with a dust shell, a massless scalar wave, an electromagnetic wave, or a neutrino wave. The formation of spacetime singularities due to nonlinear interactions and the effects of gravitational wave polarization on the nature of singularities are also explored.

In the last few years modified gravity theories have been proposed as extensions of Einstein's theory of gravity. Their main motivation is to explain the latest cosmological and astrophysical data on dark energy and dark matter. The study of general relativity at small scales has already produced important results (cf e.g. LNP 863 Quantum Gravity and Quantum Cosmology) while its study at large scales is challenging because recent and upcoming observational results will provide important information on the validity of these modified theories. In this volume, various aspects of modified gravity at large scales will be discussed: high-curvature gravity theories; general scalar-tensor theories; Galileon theories and their cosmological applications; F(R) gravity theories; massive, new massive and topologically massive gravity; Chern-Simons modifications of general relativity (including holographic variants) and higher-spin gravity theories, to name but a few of the most important recent developments. Edited and authored by leading researchers in the field and cast into the form of a multi-author textbook at postgraduate level, this volume will be of benefit to all postgraduate students and newcomers from neighboring disciplines wishing to find a comprehensive guide for their future research.

This book reviews various modified gravity models, including those with modifications in the pure gravitational sector; those involving extra fields, that is, scalar-tensor and vector-tensor gravity theories; gravity models with Lorentz symmetry breaking; and nonlocal gravity models. The authors discuss both classical and quantum aspects of these theories. The book is unique in bringing together all the current alternatives to Einstein gravity in one source and serves as an excellent starting point for graduate students and other newcomers seeking an overview. This second edition has been expanded with new results from a variety of approaches including f(R,Q,P) gravity, galileon gravity and massive gravity. Extended discussions of Lorentz-breaking terms and of non-local field theory have been added and a completely new chapter is devoted to models based on non-Riemannian geometry.

Gravity beyond general relativity / Kazuya Koyama -- Parametrizations for tests of gravity / Lucas Lombriser -- Simulation techniques / Claudio Llinares -- Approximation methods in modified gravity models / Baojiu Li -- Large-scale structure probes of modified gravity / Catherine Heymans and Gong-Bo Zhao -- Tests of gravity with galaxy clusters / Matteo Cataneo -- Towards testing gravity with cosmic voids / Yan-Chuan Cai -- Astrophysical tests of screened modified gravity / Jeremy Sakstein -- Laboratory constraints / Philippe Brax.

An up-to-date description of progress and current problems with the gravitational constant, both in terms of generalized gravitational theories and experiments either in the laboratory, using Casimir force measurements, or in space at solar system distances and in cosmological observations. Contributions cover different aspects of the state and prediction of unified theories of the physical interactions including gravitation as a cardinal link, the role of experimental gravitation and observational cosmology in discriminating between them, the problem of the precise measurement and stability of fundamental physical constants in space and time, and the gravitational constant in particular. Recent advances discussed include unified and scalar-tensor theories, theories in diverse dimensions and their observational windows, gravitational experiments in space, rotational and torsional effects in gravity, basic problems in cosmology, early universe as an arena for testing unified models, and big bang nucleosynthesis.

Magnetohydrodynamics describes dynamics in electrically conductive fluids. These occur in our environment as well as in our atmosphere and magnetosphere, and play a role in the sun's interaction with our planet. In most cases these phenomena involve turbulences, and thus are very challenging to understand and calculate. A sound knowledge is needed to tackle these problems. This work gives the basic information on turbulence in nature, comtaining the needed equations, notions and numerical simulations. The current state of our knowledge and future implications of MHD turbulence are outlined systematically. It is indispensable for all scientists engaged in research of our atmosphere and in space science.