Cosmic Acceleration
DOWNLOAD
Download Cosmic Acceleration PDF/ePub or read online books in Mobi eBooks. Click Download or Read Online button to get Cosmic Acceleration book now. This website allows unlimited access to, at the time of writing, more than 1.5 million titles, including hundreds of thousands of titles in various foreign languages. If the content not found or just blank you must refresh this page
Cosmic Acceleration
DOWNLOAD
Author : Nishant Agarwal
language : en
Publisher:
Release Date : 2011
Cosmic Acceleration written by Nishant Agarwal and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2011 with categories.
Our Universe has an exciting history of accelerated expansion. Following its inception in an event known as the big bang, the Universe underwent a phase of exponential expansion called inflation. Although precise observations of the cosmic microwave background (CMB) radiation and large-scale structure support the inflationary paradigm, the absence of a firm physical mechanism for inflation has led to a plethora of theoretical embarkments attempting to understand its genesis. Inflation lasted only for a fraction of a second, but observations suggest that thirteen billion years after inflation, the Universe began accelerating once again. This acceleration, which continues till date, is attributed to a mysterious component, dubbed dark energy, that fills up our Universe and accounts for almost 73% of the total energy density in the Universe. In this thesis we study and develop models of inflation and dark energy, in the light of current observations. We begin, in Chapter 1, with a detailed introduction to cosmic acceleration, and discuss various models of inflation and dark energy that have been studied in the literature in the recent years. In Chapter 2, we discuss how a hierarchy of Hubble flow parameters, extended to include the evolution of the inflationary sound speed, can be applied to compare a general, single-field inflationary action with cosmological observational data. In Chapter 3, we study the six-field dynamics of D3-brane inflation for a general scalar potential on the conifold, finding simple, universal behavior, such as a power law dependence for the probability of Ne e-folds of inflation. Subsequent chapters study modifications to the theory of gravity in an attempt to understand dark energy. In Chapter 4, we establish the dynamical attractor behavior in scalar-tensor theories of gravity, providing a powerful framework to analyze such theories, predicting common evolutionary characteristics that can be compared against cosmological constraints. Chapter 5 develops a cascading cosmology framework in order to study the cosmological implications of a sixdimensional (6D) theory of gravity. We find that cascading cosmology can indeed lead to an accelerating Universe. Finally, in Chapter 6, we study the issue of ghostlike instabilities in the cascading framework, and propose a mechanism to obtain flat brane and bulk solutions. We conclude in Chapter 7 with a discussion of the main results presented in this thesis.
Simulating Large Scale Structure For Models Of Cosmic Acceleration
DOWNLOAD
Author : Baojiu Li
language : en
Publisher: IOP Publishing Limited
Release Date : 2018-10-30
Simulating Large Scale Structure For Models Of Cosmic Acceleration written by Baojiu Li and has been published by IOP Publishing Limited this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-10-30 with Science categories.
Simulating Large Scale Structure for Models of Cosmic Acceleration explores alternative cosmological models and how we can learn from these as well as differentiate them from the standard cosmic model. The book also looks at the ways in which techniques can be used to accurately develop and test the model to produce new observations. This self-contained book provides a fundamental guide to researchers looking to enter the field of cosmological simulations. Postgraduate students will also find it of use as the need for numerical simulations and astronomical surveys increases. The book contains a significant amount of Professor Li's own research as well as assistance from other experts and collaborators in the field and will certainly encourage others to explore the ever-expanding world of cosmic acceleration.
Simulating Large Scale Structure For Models Of Cosmic Acceleration
DOWNLOAD
Author : Baojiu Li
language : en
Publisher:
Release Date : 2018-10-30
Simulating Large Scale Structure For Models Of Cosmic Acceleration written by Baojiu Li and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2018-10-30 with categories.
Cosmic Acceleration As Quantum Gravity Phenomenology
DOWNLOAD
Author : Chanda Rosalyn Sojourner Prescod-Weinstein
language : en
Publisher:
Release Date : 2010
Cosmic Acceleration As Quantum Gravity Phenomenology written by Chanda Rosalyn Sojourner Prescod-Weinstein and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2010 with categories.
The discovery of cosmic acceleration has prompted the need for a new understanding of cosmology. The presence of this acceleration is often described as the dark energy problem or the Lambda problem. The simplest explanation is that the acceleration is due to addition of a cosmological constant to Einstein's equation, but this resolution is unsatisfactory as it leaves several unanswered questions. Although General Relativity has been tested in the strong-field limit, the apparent dark energy may be urging us to consider experimental cosmology as such a test for large scales. In this vein, I have pursued a study of modifications to Einstein's gravity as well as possible related quantum gravity phenomenology. Not only must the details of modified gravities be worked out, but their impact on other astrophysics must be checked. For example, structure formation provides a strong test of any cosmic acceleration model because a successful dark energy model must not inhibit the development of observed large-scale structures. Traditional approaches to studies of structure formation in the presence of dark energy or a modified gravity implement the Press & Schechter formalism. I explore the potential for universality in the Press & Schechter formalism and what dark matter haloes may be able to tell us about cosmology.
Cosmic Acceleration
DOWNLOAD
Author : Ritabrata Biswas
language : en
Publisher: LAP Lambert Academic Publishing
Release Date : 2013-01
Cosmic Acceleration written by Ritabrata Biswas and has been published by LAP Lambert Academic Publishing this book supported file pdf, txt, epub, kindle and other format this book has been release on 2013-01 with categories.
After 1998 from different observational data we are quite convinced to speculate that our universe is going through an accelerating expansion. Different models are there to analyse this fact. It is to be noted that a large part of these models says about a future singularity which will occur in a finite time(coined as Big Rip). In such a surrounding what will be the fate of the compact objects like black holes? On 2004 E. Babichev et al for the first time have shown that if the fluid which is required to explain the accelerated universe(a negative pressure creating one) is assumed to accrete upon a black hole, the mass of the black hole may get reduced with time. On 2010 R. Biswas et al have shown if such fluids start to accrete the accretion disc may get fainter. Even for galactic accretion the speed of accrete in will be dominated by the speed of wind out. Even it was verified that the generalised second law of thermodynamics is not at all been violated by this process. Thermodynamics studies of black holes say that they are more unstable when they are embedded in expanding universe.
Aspects Of Cosmic Acceleration
DOWNLOAD
Author :
language : en
Publisher:
Release Date : 2019
Aspects Of Cosmic Acceleration written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2019 with categories.
The Extravagant Universe
DOWNLOAD
Author : Robert P. Kirshner
language : en
Publisher: Princeton University Press
Release Date : 2016-10-04
The Extravagant Universe written by Robert P. Kirshner and has been published by Princeton University Press this book supported file pdf, txt, epub, kindle and other format this book has been release on 2016-10-04 with Science categories.
The Extravagant Universe tells the story of a remarkable adventure of scientific discovery. One of the world's leading astronomers, Robert Kirshner, takes readers inside a lively research team on the quest that led them to an extraordinary cosmological discovery: the expansion of the universe is accelerating under the influence of a dark energy that makes space itself expand. In addition to sharing the story of this exciting discovery, Kirshner also brings the science up-to-date in a new epilogue. He explains how the idea of an accelerating universe--once a daring interpretation of sketchy data--is now the standard assumption in cosmology today. This measurement of dark energy--a quality of space itself that causes cosmic acceleration--points to a gaping hole in our understanding of fundamental physics. In 1917, Einstein proposed the "cosmological constant" to explain a static universe. When observations proved that the universe was expanding, he cast this early form of dark energy aside. But recent observations described first-hand in this book show that the cosmological constant--or something just like it--dominates the universe's mass and energy budget and determines its fate and shape. Warned by Einstein's blunder, and contradicted by the initial results of a competing research team, Kirshner and his colleagues were reluctant to accept their own result. But, convinced by evidence built on their hard-earned understanding of exploding stars, they announced their conclusion that the universe is accelerating in February 1998. Other lines of inquiry and parallel supernova research now support a new synthesis of a cosmos dominated by dark energy but also containing several forms of dark matter. We live in an extravagant universe with a surprising number of essential ingredients: the real universe we measure is not the simplest one we could imagine.
On Cosmic Acceleration Without Dark Energy
DOWNLOAD
Author :
language : en
Publisher:
Release Date : 2005
On Cosmic Acceleration Without Dark Energy written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2005 with categories.
We elaborate on the proposal that the observed acceleration of the Universe is the result of the backreaction of cosmological perturbations, rather than the effect of a negative-pressure dark energy fluid or a modification of general relativity. Through the effective Friedmann equations describing an inhomogeneous Universe after smoothing, we demonstrate that acceleration in our local Hubble patch is possible even if fluid elements do not individually undergo accelerated expansion. This invalidates the no-go theorem that there can be no acceleration in our local Hubble patch if the Universe only contains irrotational dust. We then study perturbatively the time behavior of general-relativistic cosmological perturbations, applying, where possible, the renormalization group to regularize the dynamics. We show that an instability occurs in the perturbative expansion involving sub-Hubble modes, which indicates that acceleration in our Hubble patch may originate from the backreaction of cosmological perturbations on observable scales.
Observational Tests Of Cosmic Acceleration
DOWNLOAD
Author : Alireza Hojjati
language : en
Publisher:
Release Date : 2012
Observational Tests Of Cosmic Acceleration written by Alireza Hojjati and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2012 with Cosmology categories.
The accelerating expansion of the universe is considered to be a well-established fact. However, a physical explanation of its origin is still missing. While the cosmological constant, [Lambda], is the favorite candidate, a multitude of other theories have been proposed. Rather than testing every theory against data, one can adapt phenomenological approaches aimed at testing [Lambda]. Adopting a model-independent approach to studying dark energy, we have investigated the utility of wavelets for constraining the redshift evolution of the dark energy equation of state from a combination of the type Ia supernovae, cosmic microwave background (CMB) and baryon acoustic oscillation (BAO) data. We have shown that sharp deviations from w[subscript {Lambda}]=-1 can be detected efficiently. Applying this method to the "Constitution" SNe data, combined with the CMB data from WMAP and BAO data from SDSS, provided only weak hints of dark energy dynamics. Future weak lensing surveys will have the ability to measure the growth of large scale structure with accuracy sufficient for discriminating between different theories of dark energy and modified gravity. The growth of structure can be tested, in a model-independent way, by parametrizing the evolution equations of cosmological perturbations. At the linear level, this can be achieved by introducing two scale- and time-dependent functions (MG functions). We have consistently implemented the parametrized equations in the commonly used public codes, CAMB and CosmoMC, while preserving the covariant conservation of the energy-momentum. As a demonstration, we have obtained joint constraints on the neutrino mass and parameters of a scalar-tensor gravity model from the CMB, SNe and the correlation of CMB with large scale structure. We have performed a Principal Component Analysis (PCA) to find the eigenmodes and eigenvalues of the forecasted covariance matrix of the MG functions for surveys like DES and LSST. By examining the eigenmodes, we can learn about the scales and redshifts where the surveys are most sensitive to modification of the growth. We have considered the impact of some of the systematic effects expected in weak lensing surveys. We have demonstrated the utility of the PCA as an efficient way of storing information about the linear growth of perturbations.
Is Cosmic Acceleration Telling Us Something About Gravity
DOWNLOAD
Author :
language : en
Publisher:
Release Date : 2006
Is Cosmic Acceleration Telling Us Something About Gravity written by and has been published by this book supported file pdf, txt, epub, kindle and other format this book has been release on 2006 with categories.
Among the possible explanations for the observed acceleration of the universe, perhaps the boldest is the idea that new gravitational physics might be the culprit. In this colloquium I will discuss some of the challenges of constructing a sensible phenomenological extension of General Relativity, give examples of some candidate models of modified gravity and survey existing observational constraints on this approach. I will conclude by discussing how we might hope to distinguish between modifications of General Relativity and dark energy as competing hypotheses to explain cosmic acceleration.