Modified Gravity And Cosmology On The Largest Scales
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Modified Gravity And Cosmology On The Largest Scales
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Author : Alexandra Eileen Terrana
language : en
Publisher:
Release Date : 2017
Modified Gravity And Cosmology On The Largest Scales written by Alexandra Eileen Terrana and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2017 with categories.
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.
Modifications Of Einstein S Theory Of Gravity At Large Distances
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Author : Eleftherios Papantonopoulos
language : en
Publisher: Springer
Release Date : 2014-11-08
Modifications Of Einstein S Theory Of Gravity At Large Distances written by Eleftherios Papantonopoulos and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2014-11-08 with Science categories.
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.
Modified Gravity And Cosmology
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Author : Emmanuel N. Saridakis
language : en
Publisher: Springer Nature
Release Date : 2021-12-10
Modified Gravity And Cosmology written by Emmanuel N. Saridakis and has been published by Springer Nature this book supported file pdf, txt, epub, kindle and other format this book has been release on 2021-12-10 with Science categories.
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.
Modified Gravity Progresses And Outlook Of Theories Numerical Techniques And Observational Tests
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Author : Baojiu Li
language : en
Publisher: World Scientific
Release Date : 2019-10-10
Modified Gravity Progresses And Outlook Of Theories Numerical Techniques And Observational Tests written by Baojiu Li and has been published by World Scientific this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019-10-10 with Science categories.
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.
Studies Into The Nature Of Cosmic Acceleration
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Author : Jason Nicholas Dossett
language : en
Publisher:
Release Date : 2013
Studies Into The Nature Of Cosmic Acceleration written by Jason Nicholas Dossett and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013 with Cosmology categories.
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.
Dark Energy And The Formation Of The Large Scale Structure Of The Universe
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Author : Jérôme Gleyzes
language : en
Publisher: Springer
Release Date : 2016-06-28
Dark Energy And The Formation Of The Large Scale Structure Of The Universe written by Jérôme Gleyzes and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-06-28 with Science categories.
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.
Structure Formation In Modified Gravity Cosmologies
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Author : Alexandre Barreira
language : en
Publisher: Springer
Release Date : 2016-05-03
Structure Formation In Modified Gravity Cosmologies written by Alexandre Barreira and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-05-03 with Science categories.
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.
Multiple Messengers And Challenges In Astroparticle Physics
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Author : Roberto Aloisio
language : en
Publisher: Springer
Release Date : 2018-02-27
Multiple Messengers And Challenges In Astroparticle Physics written by Roberto Aloisio and has been published by Springer this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-02-27 with Science categories.
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.
Testing Gravity With Cosmology
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Author : Georgios Valogiannis
language : en
Publisher:
Release Date : 2020
Testing Gravity With Cosmology written by Georgios Valogiannis and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2020 with categories.
In the era of precision cosmology, a wide range of cosmological surveys, such as the LSST, DESI, Euclid and WFIRST will precisely probe the large-scale structure of the universe, shedding light on the nature of the dark sectors. Given how sensitively the growth of structure depends on the nature of the underlying gravitational field, this will be a unique opportunity to constrain the so-called Modified Gravity models (MG), that are theoretical alternatives to dark energy, which attempt to explain cosmic acceleration through a large-scale modification to General Relativity. In order to fully utilize the wealth of incoming data, however, theoretical predictions of structure formation in such alternative scenarios are necessary. Due to the existence of an additional degree of freedom that these models introduce, N-body simulations prove to be highly computationally expensive. In the first chapter of this thesis, we discuss how we can overcome this issue by using Lagrangian hybrid techniques, which can lead to a speed-up by 2 orders of magnitude, compared to the conventional tools, while still achieving % level of accuracy. Then, in chapter 2 we proceed to introduce novel statistics that can help us more confidently detect MG signals hidden in cosmic density fields, by up-weighting the significance of cosmic voids, where the MG-LambdaCDM degeneracy is broken. In the scales where structure formation is analytically tractable, finally, we show that we can make accurate analytical predictions for the two-point statistics of halos in MG, using Lagrangian perturbation theory and the Gaussian Streaming Model, simultaneously capturing, for the first time in modified gravity, the effects of both halo-bias (in chapter 3) and redshift space distortions (in chapter 4), effects crucial for the interpretation of photometric and spectroscopic observations. Our results demonstrate that a series of analytical, semi-analytical and simulation-based tools can be utilized in order to dramatically improve our understanding of the nature of cosmic acceleration and gravity at cosmic scales.
Extensions Of F R Gravity
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Author : Tiberiu Harko
language : en
Publisher: Cambridge University Press
Release Date : 2018-11-08
Extensions Of F R Gravity written by Tiberiu Harko and has been published by Cambridge University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-11-08 with Science categories.
Recent cosmological observations have posed a challenge for traditional theories of gravity: what is the force driving the accelerated expansion of the universe? What if dark energy or dark matter do not exist and what we observe is a modification of the gravitational interaction that dominates the universe at large scales? Various extensions to Einstein's General Theory of Relativity have been proposed, and this book presents a detailed theoretical and phenomenological analysis of several leading, modified theories of gravity. Theories with generalised curvature-matter couplings are first explored, followed by hybrid metric-Palatini gravity. This timely book first discusses key motivations behind the development of these modified gravitational theories, before presenting a detailed overview of their subsequent development, mathematical structure, and cosmological and astrophysical implications. Covering recent developments and with an emphasis on astrophysical and cosmological applications, this is the perfect text for graduate students and researchers.