Download or read book Modified Gravity and Cosmology on the Largest Scales written by Alexandra Eileen Terrana and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation presents a series of my contributions to research in theoretical cosmology, focusing on aspects of the very large scale universe, particularly dark energy, cosmic acceleration, modified gravity, and cosmic variance. Following an overview of the current understanding of the standard cosmological model in chapter 1, three pertinent topics are discussed in detail. A common theme among all chapters is the desire to explain the properties of the universe on the largest scales. One of the biggest mysteries on large scales is the need for dark energy to explain the observed accelerated expansion of the late universe. The unsatisfying explanation offered by the standard cosmological model and the associated enormous fine tuning problem have driven considerable interest in infrared (long-distance) modifications of general relativity. In this work, we consider a particularly well motivated modified theory, massive gravity, in which the modification is to simply assume that the particle mediating the gravitational force has a non-zero mass. For a mass on the order of the Hubble constant, this theory offers an alternative explanation of the accelerated cosmic expansion. Chapter 2 lays the theoretical groundwork for massive gravity, summarizing its history and formalism. A fundamental challenge for any modified gravity theory is sequestering the modification to large enough distance scales, so that the predictions match general relativity on solar system scales where it has been tested to high precision. Chapter 3 provides a detailed analysis of massive gravity's ability to screen its extra degrees of freedom, allowing for continuity with general relativity on short distance scales. Further, in chapter 4, we explore the cosmological production and propagation of gravitational waves in an extension of massive gravity, bigravity, determining whether there may be any testable deviations from general relativity. Understanding these predictions is crucial, as there is now a vigorous observational program to probe possible deviations from our standard model. As rapid progress in observational cosmology unfolds, not only is it paramount to construct viable modified gravity theories to test against general relativity, it is necessary to explore which observational methods will be the most powerful for constraining them. This dissertation contains progress on both of these fronts: analyzing potential modified gravity theories, and analyzing potential novel observational probes of the large scale universe. Chapter 5 provides the theoretical framework for one such novel probe, the large scale kinetic Sunyaev-Zeldovich effect. This effect is particularly intriguing because of its ability to overcome cosmic variance, and thus help us unlock the secrets of the universe on the largest scales.
Download or read book Modifications of Einstein s Theory of Gravity at Large Distances written by Eleftherios Papantonopoulos and published by Springer. This book was released on 2014-11-08 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Modified Gravity and Cosmology written by Emmanuel N. Saridakis and published by Springer Nature. This book was released on 2021-12-10 with total page 631 pages. Available in PDF, EPUB and Kindle. Book excerpt: With a focus on modified gravity this book presents a review of the recent developments in the fields of gravity and cosmology, presenting the state of the art, high-lighting the open problems, and outlining the directions of future research. General Relativity and the ΛCDM framework are currently the standard lore and constitute the concordance paradigm of cosmology. Nevertheless, long-standing open theoretical issues, as well as possible new observational ones arising from the explosive development of cosmology in the last two decades, offer the motivation and lead a large amount of research to be devoted in constructing various extensions and modifications. In this review all extended theories and scenarios are first examined under the light of theoretical consistency, and are then applied in various geometrical backgrounds, such as the cosmological and the spherical symmetric ones. Their predictions at both the background and perturbation levels, and concerning cosmology at early, intermediate and late times, are then confronted with the huge amount of observational data that astrophysics and cosmology has been able to offer in the last two decades. Theories, scenarios and models that successfully and efficiently pass the above steps are classified as viable and are candidates for the description of Nature, allowing readers to get a clear overview of the state of the art and where the field of modified gravity is likely to go. This work was performed in the framework of the COST European Action “Cosmology and Astrophysics Network for Theoretical Advances and Training Actions” - CANTATA.
Download or read book Modified Gravity Progresses And Outlook Of Theories Numerical Techniques And Observational Tests written by Baojiu Li and published by World Scientific. This book was released on 2019-10-10 with total page 324 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Dark Energy written by Luca Amendola and published by Cambridge University Press. This book was released on 2010-06-10 with total page 507 pages. Available in PDF, EPUB and Kindle. Book excerpt: Introducing the theoretical ideas, observational methods and results in dark energy, this textbook is a thorough introduction to dark energy for graduate courses.
Download or read book Dark Energy and the Formation of the Large Scale Structure of the Universe written by Jérôme Gleyzes and published by Springer. This book was released on 2016-06-28 with total page 124 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis presents several significant new results that shed light on two major puzzles of modern cosmology: the nature of inflation, the very early phase of the universe that is thought to have given rise to the large-scale structures that we observe today; and that of the current accelerated expansion. In particular, it develops a clean method for characterizing linear cosmological perturbations for general theories where gravity is modified and/or affected by a new component, called dark energy, responsible for the accelerated expansion. It proposes a new extension to what were long thought to be the most general scalar field theories devoid of instabilities, and demonstrates the robustness of the relation between the energy scale of inflation and the predicted amplitude of gravitational waves. Finally, it consolidates a set of consistency relations between correlation functions of the cosmological density field and investigates the phenomenological consequences of their potential violation. Presented in a clear, succinct and rigorous style, each of these original results is both profound and important and will leave a deep mark on the field.
Download or read book Modified Gravity written by Baojiu Li and published by World Scientific Publishing Company. This book was released on 2019 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Expansion of the Universe written by Steff Jaywan and published by Dedona Publishing. This book was released on with total page 43 pages. Available in PDF, EPUB and Kindle. Book excerpt: The universe is a vast and enigmatic expanse, filled with countless mysteries that have intrigued scientists and philosophers for centuries. One of the most profound discoveries of modern cosmology is that the universe is not only expanding but doing so at an accelerating rate. This revelation has reshaped our understanding of the cosmos and introduced the concept of dark energy as a dominant force driving this acceleration. In this book, we embark on a journey through the history of cosmological thought, from the early observations that hinted at an expanding universe to the groundbreaking discoveries that revealed its acceleration. We will explore the role of the cosmological constant, a term introduced by Einstein in his equations of General Relativity, which has come to be associated with dark energy. We begin with a foundational understanding of the universe's expansion, delving into the Big Bang theory and the key observations that support it. From there, we examine the pivotal role of the cosmological constant and its implications for the structure and fate of the universe. As we navigate through the complexities of dark energy and its various theoretical models, we will also address the challenges and alternative theories that scientists are exploring to explain this cosmic acceleration. Finally, we will consider the future of cosmological research, highlighting the ongoing quests to unravel the mysteries that still elude us.
Download or read book Studies Into the Nature of Cosmic Acceleration written by Jason Nicholas Dossett and published by . This book was released on 2013 with total page 536 pages. Available in PDF, EPUB and Kindle. Book excerpt: Since its discovery more than a decade ago, the problem of cosmic acceleration has become one of the largest in cosmology and physics as a whole. An unknown dark energy component of the universe is often invoked to explain this observation. Mathematically, this works because inserting a cosmic fluid with a negative equation of state into Einstein's equations provides an accelerated expansion. There are, however, alternative explanations for the observed cosmic acceleration. Perhaps the most promising of the alternatives is that, on the very largest cosmological scales, general relativity needs to be extended or a new, modified gravity theory must be used. Indeed, many modified gravity models are not only able to replicate the observed accelerated expansion without dark energy, but are also more compatible with a unified theory of physics. Thus it is the goal of this dissertation to develop and study robust tests that will be able to distinguish between these alternative theories of gravity and the need for a dark energy component of the universe. We will study multiple approaches using the growth history of large-scale structure in the universe as a way to accomplish this task. These approaches include studying what is known as the growth index parameter, a parameter that describes the logarithmic growth rate of structure in the universe, which describes the rate of formation of clusters and superclusters of galaxies over the entire age of the universe. We will explore the effectiveness of this parameter to distinguish between general relativity and modifications to gravity physics given realistic expectations of results from future experiments. Next, we will explore the modified growth formalism wherein deviations from the growth expected in general relativity are parameterized via changes to the growth equations, i.e. the perturbed Einstein's equations. We will also explore the impact of spatial curvature on these tests. Finally, we will study how dark energy with some unusual properties will affect the conclusiveness of these tests.
Download or read book Modifications of Einstein s Theory of Gravity at Large Distances written by Eleftherios Papantonopoulos and published by Springer. This book was released on 2014-11-04 with total page 435 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Cosmological Physics written by J. A. Peacock and published by Cambridge University Press. This book was released on 1999 with total page 700 pages. Available in PDF, EPUB and Kindle. Book excerpt: A comprehensive and authoritative introduction to contemporary cosmology for advanced undergraduate and graduate students.
Download or read book Simulating Large Scale Structure for Models of Cosmic Acceleration written by Baojiu Li and published by . This book was released on 2018-10-30 with total page 198 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Multiple Messengers and Challenges in Astroparticle Physics written by Roberto Aloisio and published by Springer. This book was released on 2018-02-27 with total page 554 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book, designed as a tool for young researchers and graduate students, reviews the main open problems and research lines in various fields of astroparticle physics: cosmic rays, gamma rays, neutrinos, cosmology, and gravitational physics. The opening section discusses cosmic rays of both galactic and extragalactic origin, examining experimental results, theoretical models, and possible future developments. The basics of gamma-ray astronomy are then described, including the detection methods and techniques. Galactic and extragalactic aspects of the field are addressed in the light of recent discoveries with space-borne and ground-based detectors. The review of neutrinos outlines the status of the investigations of neutrino radiation and brings together relevant formulae, estimations, and background information. Three complementary issues in cosmology are examined: observable predictions of inflation in the early universe, effects of dark energy/modified gravity in the large-scale structure of the universe, and neutrinos in cosmology and large-scale structures. The closing section on gravitational physics reviews issues relating to quantum gravity, atomic precision tests, space-based experiments, the strong field regime, gravitational waves, multi-messengers, and alternative theories of gravity.
Download or read book Generalized Perturbations in Modified Gravity and Dark Energy written by Jonathan Pearson and published by Springer Science & Business Media. This book was released on 2013-09-20 with total page 213 pages. Available in PDF, EPUB and Kindle. Book excerpt: When predictions of Einstein's theory of General Relativity are compared against observations of our Universe, a huge inconsistency is found. The most popular fix for this inconsistency is to "invent" around 94% of the content of the universe: dark matter and dark energy. The dark energy is some exotic substance responsible for the apparent observed acceleration of the Universe. Another fix is to modify the theory of gravity: it is entirely plausible that Einstein's theory of General Relativity breaks down on cosmological scales, just as Newton's theory of gravity breaks down in the extreme gravitational field of the Sun. There are many alternative theories of gravity, each with the aim of describing observations of our Universe where General Relativity fails. Whether it is dark energy or some modified theory of gravity, it is clear that there is some "dark sector" in the Universe. In this thesis the author constructs a unifying framework for understanding the observational impact of general classes of dark sector theories, by formulating equations of state for the dark sector perturbations.
Download or read book Aspects of Modified Gravity written by Shohreh Rahmati and published by . This book was released on 2017 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: To date, General Relativity provides the best description of the gravitational interaction. It can accurately describe the motion of the planets within the solar system. However, on large scales general relativity is unable to explain the accelerating expansion of the Universe. Furthermore, so far, no complete self-consistent quantum theory of gravity based on General Relativity has been constructed. This has motivated physicists to explore alternative theories of gravity. In this thesis, I explore three different problems confronting gravitational physics. First, I explore a gauge theory of gravity. In these models one has to choose a gauge group and localize its global symmetries. In this thesis I consider a Yang-Mills gauge gravity of the conformal group SO(4,2). This work was done in collaboration with J. Gegenberg and S. Seahra. In the thesis, I show the derivation of the equations of motion and investigate the cosmological solutions in the case that the matter content of the Universe is a mixture of dust and radiation. Our model predicts a big bounce in the early Universe followed by a period of nearly exponential slow roll inflation that can last long enough to explain the large scale homogeneity of the cosmic microwave background. Furthermore, our model incorporates a de Sitter-like accelerating phase in the late Universe that agrees with observations. Second, I explore a toy model of gravity. This work is in collaboration with V. Husain and J. Ziprick. General relativity in four-dimensional spacetime is a complicated theory to quantize. Therefore, it is useful to study simpler models. Einstein gravity in three dimensions has been a subject of much study, especially for the purpose of quantization. However, there are no local propagating degrees of freedom in three dimensions. It is fruitful to study three-dimensional gravitational theories with local field degrees of freedom. I consider here a method for obtaining local degrees of freedom: three dimensional general relativity coupled to a pressureless “dust”. The dust time gauge is imposed with the upshot that the gravitational part of the Hamiltonian constraint becomes the physical Hamiltonian. This yields an extra degree of freedom in the metric field. In the thesis, I examine the action in canonical form and derive the evolution equations for the spatial metric and its conjugate momentum. Linearizing the equations about the flat background and imposing the transverse (or traceless) gauges indicates that the extra degree of freedom in the metric is a scalar mode and is ultralocal. Finally, I examine parametric resonance in cosmology, in collaboration with S. Seahra. According to dynamical dark energy models or theories of quantum gravity, it can be possible that kinetic terms appearing in matter actions get modified at high or low energies. The modification of the matter kinetic term can directly influence the parametric resonance and therefore the preheating phase near the end of inflation. Preheating is a process required to reheat the universe and create elementary particles. To incorporate exotic kinetic terms into this scenario, one can modify the action of the inflaton, the reheaton, or both. In the last part of this thesis, I study the effects of nonstandard kinetic terms from several different models on resonant preheating.
Download or read book Structure Formation in Modified Gravity Cosmologies written by Alexandre Barreira and published by Springer. This book was released on 2016-05-03 with total page 234 pages. Available in PDF, EPUB and Kindle. Book excerpt: This unique thesis covers all aspects of theories of gravity beyond Einstein’s General Relativity, from setting up the equations that describe the evolution of perturbations, to determining the best-fitting parameters using constraints like the microwave background radiation, and ultimately to the later stages of structure formation using state-of-the-art N-body simulations and comparing them to observations of galaxies, clusters and other large-scale structures. This truly ground-breaking work puts the study of modified gravity models on the same footing as the standard model of cosmology. Since the discovery of the accelerating expansion of the Universe, marked by the awarding of the 2011 Nobel Prize in Physics, there has been a growing interest in understanding what drives that acceleration. One possible explanation lies in theories of gravity beyond Einstein’s General Relativity. This thesis addresses all aspects of the problem, an approach that is crucial to avoiding potentially catastrophic biases in the interpretation of upcoming observational missions.
Download or read book Dark Matter and Dark Energy written by Sabino Matarrese and published by Springer Science & Business Media. This book was released on 2011-02-10 with total page 413 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book brings together reviews from leading international authorities on the developments in the study of dark matter and dark energy, as seen from both their cosmological and particle physics side. Studying the physical and astrophysical properties of the dark components of our Universe is a crucial step towards the ultimate goal of unveiling their nature. The work developed from a doctoral school sponsored by the Italian Society of General Relativity and Gravitation. The book starts with a concise introduction to the standard cosmological model, as well as with a presentation of the theory of linear perturbations around a homogeneous and isotropic background. It covers the particle physics and cosmological aspects of dark matter and (dynamical) dark energy, including a discussion of how modified theories of gravity could provide a possible candidate for dark energy. A detailed presentation is also given of the possible ways of testing the theory in terms of cosmic microwave background, galaxy redshift surveys and weak gravitational lensing observations. Included is a chapter reviewing extensively the direct and indirect methods of detection of the hypothetical dark matter particles. Also included is a self-contained introduction to the techniques and most important results of numerical (e.g. N-body) simulations in cosmology. " This volume will be useful to researchers, PhD and graduate students in Astrophysics, Cosmology Physics and Mathematics, who are interested in cosmology, dark matter and dark energy.
