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Dissertations / Theses on the topic 'F(R) gravity'

Author: Grafiati

Published: 4 June 2021

Last updated: 14 February 2022

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1

Bourhrous, Hassan. "CMB tensor anisotropies in f(R) gravity." Master's thesis, University of Cape Town, 2014. http://hdl.handle.net/11427/4866.

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2

Vilardi, Demetrio. "F(r) approximation in asymptotically safe quantum gravity." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2013. http://amslaurea.unibo.it/5619/.

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3

Nojiri, Shin'ichi, та Sergei D. Odintsov. "Modified f(R) gravity unifying R^m inflation with the ΛCDM epoch". American Physical Society, 2008. http://hdl.handle.net/2237/11276.

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4

Bamba, Kazuharu, Shin'ichi Nojiri, and Sergei D. Odintsov. "Inflationary cosmology and the late-time accelerated expansion of the universe in nonminimal Yang-Mills- F(R) gravity and nonminimal vector-F(R) gravity." American Physical Society, 2008. http://hdl.handle.net/2237/11280.

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5

Kandhai, Sulona. "Investigating the parameter space of viable models for f(R) gravity." Doctoral thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/31181.

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The accelerated expansion of spacetime intuitively points to the existence of new, unknown energy fields pervading the universe, but it is has also spurred the growth of the research field of modified gravity theories. Of these, f(R) theories of gravity is the first and simplest modification to General Relativity, and have been studied extensively for their astrophysical and cosmological predictions. Power law f(R) modifications have been shown to exhibit desirable characteristics, producing the late time accelerated expansion as well as satisfying local tests of gravity. However, there is wid

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6

Gidelew, Amare Abebe. "Covariant perturbations in f (R) - gravity of multi-component fluid cosmologies." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/4884.

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Includes abstract.<br>Includes bibliographical references (leaves 82-84).<br>We study the evolution of scalar cosmological perturbations in the 1+3 Covariant Gauge-Invariant formalism for generic f(R) theories of gravity. Working in the energy frame of the total matter, we give a complete set equations describing the evolution of matter and curvature fluctuations for a multi-fluid cosmological medium. We then specialize to a radiation-dust fluid described by barotropic equations of state. We apply the perturbation equations around a background solution of Rⁿ gravity and look at exact solutions

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7

Dlamini, Simthembile. "Evolution of matter density perturbations in viable f (R) theories of gravity." Master's thesis, Faculty of Science, 2019. http://hdl.handle.net/11427/31500.

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In the ΛCDM model, the late-time accelerated expansion of the Universe is explained via a dark energy fluid in the form of a cosmological constant. Such a cosmological constant dominates the energy budget of the Universe today, and yet, it is still a poorly understood species because it is not observed yet. A competitive theoretical approach to understand this is via the so-called f (R) extended theories of gravity, which explain the late acceleration epoch of the Universe resorting to a geometrical modification of the field equations. We illustrate how f (R) theories are constructed and how b

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8

Nzioki, Anne Marie. "1+1+2 covariant approach to gravitational lensing in f(R) gravity." Master's thesis, University of Cape Town, 2009. http://hdl.handle.net/11427/17116.

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Includes bibliographical references (pages 64-67).<br>In this thesis, we develop the 1 + 1 + 2 formalism, a technique originally devised for General Relativity, to treat spherically symmetric spacetimes in for fourth order theories of gravity. Using this formalism, we derive equations for a static and spherically symmetric spacetime for general f(R) gravity. We apply these master eqautions to derive some exact solutions, which are used to gain insight on Birkhoff's theorem in this framework. Additionally, we derive a covariant form of the lensing angle for a specific spherically symmetric solu

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9

Aboelhassan, Sheref Nasereldin. "Probing the cosmological dynamics of a logarithmic f (R) theory of gravity." Master's thesis, University of Cape Town, 2015. http://hdl.handle.net/11427/15727.

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Includes bibliographical references<br>In this thesis we make a contribution in the area of Extended Theories of Gravity (ETG) by studying the dynamics of the R ln R model. We draw attention to the importance of introducing complete alternative theories of gravity and studying the possible geometrical origin of Dark Energy (unknown form of energy), which is commonly thought to be responsible for the present epoch of accelerated expansion that our universe undergoes. The first chapter of the thesis is an introduction to one of the most successful models in the realm of cosmology i.e. the CDM mo

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10

Reeves, Edward. "Aspects of modified gravity." Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/aspects-of-modified-gravity(69d3a682-1dbd-4876-9b28-dd8767aea20a).html.

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11

Berry, Christopher P. L. "Exploring gravity." Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245139.

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Gravitation is the dominant influence in most astrophysical interactions. Weak-field interactions have been extensively studied, but the strong-field regime remains largely unexplored. Gravitational waves (GWs) are an excellent means of accessing strong-field regions. We investigate what we can learn about both astrophysics and gravitation from strong-field tests and, in particular, GWs; we focus upon extreme-mass-ratio (EMR) systems where a small body orbits a much more massive one. EMR bursts, a particular class of GW signals, could be used to determine the properties of massive black holes

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12

Castaneda, C. Leonardo [Verfasser]. "Some Aspects in Cosmological Perturbation Theory and f (R) Gravity / Leonardo Castaneda C." Bonn : Universitäts- und Landesbibliothek Bonn, 2016. http://d-nb.info/111988893X/34.

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13

Arnold, Christian [Verfasser], and Volker [Akademischer Betreuer] Springel. "Hydrodynamical cosmological simulations in f(R) modified gravity / Christian Arnold ; Betreuer: Volker Springel." Heidelberg : Universitätsbibliothek Heidelberg, 2017. http://d-nb.info/1180985893/34.

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14

Oliveira, Thiago Bruno Rafael de Freiras. "Teorias f(R) de gravidade na formula??o de Palatini." Universidade Federal do Rio Grande do Norte, 2010. http://repositorio.ufrn.br:8080/jspui/handle/123456789/18587.

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Made available in DSpace on 2015-03-03T15:15:24Z (GMT). No. of bitstreams: 1 ThiagoBRFO_DISSERT.pdf: 776732 bytes, checksum: 79a4002c3c2d724d3d1651680816802b (MD5) Previous issue date: 2010-07-01<br>Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior<br>In this dissertation, after a brief review on the Einstein s General Relativity Theory and its application to the Friedmann-Lemaitre-Robertson-Walker (FLRW) cosmological models, we present and discuss the alternative theories of gravity dubbed f(R) gravity. These theories come about when one substitute in the Einstein-Hilbert ac

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15

Nojiri, Shin'ichi, and Sergei D. Odintsov. "Future evolution and finite-time singularities in F(R) gravity unifying inflation and cosmic acceleration." American Physical Society, 2008. http://hdl.handle.net/2237/11279.

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16

Lopes, Rafael Christ de Castro. "Estudo do raio de turnaround em teorias f(R)." Universidade de São Paulo, 2019. http://www.teses.usp.br/teses/disponiveis/43/43134/tde-21032019-154839/.

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Nós investigamos o raio de turnaround, a distância do centro da estrutura cósmica até a casca que está se descolando do fluxo de Hubble em um dado tempo, no contexto do modelo de colapso esférico, tanto em Relatividade Geral e em Gravidade Modificada, em particular no cenário f(R) chamado de modelo de Hu-Sawicki. O próximo passo foi investigar a relação entre este raio e a massa de virial de estruturas cósmicas no contexto do modelo LCDM e no modelo f(R) de gravidade modificada.<br>We investigate the turnaround radius, the distance from the center of the cosmic structure to the shell that is

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17

Castello, Sveva. "Galaxy clusters and cosmic voids in modified gravity scenarios." Thesis, Uppsala universitet, Teoretisk astrofysik, 2019. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-377319.

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The so-called 'cosmic web', comprising cosmic voids and galaxy clusters, has been proven to be extremely sensitive to deviations from General Relativity. This could be further investigated by future large-scale surveys, such as with the European Space Agency satellite Euclid. In this study, the parameter |fR0| from f(R) gravity is constrained by considering the Euclid survey specications to predict the observed numbers of voids and clusters in bins of redshift, mass and, only for voids, density contrast. From these values, the Fisher matrix is computed for three values of |fR0|, 10-4, 10-6 and

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18

Dev, Abha, Deepak Jain, S. Jhingan, S. Nojiri, M. Sami, and I. Thongkool. "Delicate f(R) gravity models with a disappearing cosmological constant and observational constraints on the model parameters." American Physical Society, 2008. http://hdl.handle.net/2237/11278.

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19

Moslehi, Sadegh. "Mach’s principle and modified gravity." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018.

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It was after the discussion about the nature of matter and space among scientists and philosophers,meanwhile Newton presented more accurate theories based on his equations. Newton believed that time and space are absolute, and he based his principles upon this belief.After him many scientists presented sometimes complementary or different theories.Mach was one of the famous scientists who had another ideas different from Newton, that later used and considered by Einstein as the completion of general relativity and named it Mach's principle. Although later Einstein rejected some subjects of thi

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20

Nojiri, Shin'ichi, and Sergei D. Odintsov. "Modified f (R) gravity consistent with realistic cosmology: From a matter dominated epoch to a dark energy universe." American Physical Society, 2006. http://hdl.handle.net/2237/8840.

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21

Ma, Yue. "Équations d'onde nonlinéaires de type Klein-Gordon : application à la théorie f(R) de la gravitation." Thesis, Paris 6, 2014. http://www.theses.fr/2014PA066379/document.

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Cette thèse est composée de deux parties qui sont relativement indépendantes l’un de l’autre. Dans la première partie,une autre théorie de la gravitation que l’on appelle la gravité de f(R), est étudiée. Une première analyse mathématique est discutée sur cette théorie, y compris la formulation mathématique du problème de Cauchy, la discussion sur le choix du couplage, et la formulation mathématique des équations différentielles. Ce système des équations différentielles est de quatrième ordre et très impliqué. Pour pouvoir établir l’existence locale, une série de transformations et reformulatio

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22

Moraes, Bruno. "Les mystères de l'énergie noire." Thesis, Montpellier 2, 2010. http://www.theses.fr/2010MON20032.

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L'un des plus grands problèmes ouverts de la cosmologie moderne est l'origine de l'expansion accélérée de l'Univers, découverte en 1998. L'explication théorique la plus simple repose sur l'introduction d'une constante cosmologique Λ. Ce modèle, connu sous le nom de Lambda CDM, est en accord avec les différentes observations liées à l'expansion accélérée. Cependant, il présente des problèmes d'ordre théorique. Par conséquent, plusieurs alternatives, connues collectivement sous le nom de {it modèles d'énergie noire}, ont été proposées pour expliquer cette accélération. Plusieurs d'entre eux rest

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23

Castello, Sveva. "The Largest Void and Cluster in Non-Standard Cosmology." Thesis, Uppsala universitet, Teoretisk astrofysik, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-412411.

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We employ observational data about the largest cosmic void and most massive galaxy cluster known to date, the 'Cold Spot' void and the 'El Gordo' cluster, in order to constrain the parameter |fR0| from the f(R) gravity formulation by Hu and Sawicki and the matter power spectrum normalization at present time, σ8. We obtain the marginalized posterior distribution for these two parameters through a Markov Chain Monte Carlo analysis, where the likelihood function is modeled through extreme value statistics. The prior distribution for the additional cosmological parameters included in the computati

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24

Pettinari, Paolo. "Teorie della gravitazione f(R)." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/9118/.

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Tra tutti i fenomeni naturali osservabili, ne era presente uno particolarmente interessante e con il quale si aveva diretto contatto quotidianamente: la gravità. Dopo le innumerevoli osservazioni astronomiche effettuate da Galileo, fu Newton nel diciassettesimo secolo a capire che il moto dei pianeti era governato dalle medesime leggi che descrivono la caduta dei gravi sulla Terra e fu quindi lui che ci fornì una prima teoria della gravità con la quale si spiegarono le orbite dei pianeti con ottima precisione. Grazie al contributo di Einstein, la teoria si rinnovò e si arricchì, ma rimase p

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25

Franciolini, Gabriele. "Inflazione cosmologica R^2." Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2015. http://amslaurea.unibo.it/8857/.

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Lo scopo di questa tesi è illustrare il paradigma dell’inflazione cosmologica descrivendo in particolare la teoria dell’inflazione R^2. In una prima sezione si fa riferimento al contesto della relatività generale per descrivere l’universo su larga scala. Vengono prese in esame le ipotesi utilizzate per ottenere il modello standard della cosmologia e le principali proprietà che da esso possono essere ricavate. Si focalizza quindi l’analisi sulla descrizione dell’universo primordiale da cui traggono origine le ipotesi dell’esistenza dell’epoca inflazionaria esponendo, in particolare, come ques

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26

Chen, Yow-Chun, and 陳祐君. "Observational Constraints on Viable f(R) Gravity Models." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/r5v37x.

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27

HSU, WEI-CHENG, and 徐偉程. "Thermodynamics of f(R) Gravity with Disformal Relation." Thesis, 2017. http://ndltd.ncl.edu.tw/handle/a7jbc9.

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28

Wu, Yen-Ting, and 吳彥廷. "Constraining f(R) Gravity via Structure Formation of the Universe." Thesis, 2011. http://ndltd.ncl.edu.tw/handle/55760883585033982463.

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碩士<br>國立臺灣大學<br>物理研究所<br>99<br>We investigate the evolution of the cosmological perturbations in f(R) gravity, an alternative to dark energy for explaining the late-time cosmic acceleration. It is conventional to use GR as the approximation to calculate cosmological perturbations in f(R) gravity at early times. For the late-time universe, it is to use the approximate formula proposed by Tsujikawa (termed Tsu) to calculate the matter density perturbation. The method with GR and Tsu is conventional to calculate the matter density perturbation and the matter power spectrum. In this thesis we prop

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29

Lin, Wei-Ting, and 林韋廷. "Observational Constraints on the f(R) Theory of Modified Gravity." Thesis, 2010. http://ndltd.ncl.edu.tw/handle/24420002292902226191.

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碩士<br>國立臺灣大學<br>物理研究所<br>98<br>In this thesis we constrain the designer f(R) models by the observations in both cosmological and local scales. For the cosmological observation constraints, we find that although the designer f(R) can generate any desired cosmic expansion his-tory, it suffers from the fine-tuning problem in order to fit the large scale structure constraints well. For local gravity constraints, so far we do search out the viable designer f(R) models that can satisfy the local gravity constraints but would be indistinguishable from the ΛCDM model even considering the observations

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30

Novák, Jan. "Matematická teorie perturbací v kosmologii." Doctoral thesis, 2015. http://www.nusl.cz/ntk/nusl-350107.

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We deal with cosmological perturbation theory in my work. We investigate General Theory of Relativity in Higher Dimensions in the Chapter 1. I mention GHP-formalism and algebraical classification of spacetimes. I use spinors to show that spacetimes of dimension 4 are special. I discuss also Kundt spacetimes, which are interesting for perturbation theory of black holes. I work with perturbations of FLRW ST's in GHP formalism in Chapter 2, which we want to use in Cosmological Inflation. The final part of my thesis is connected with scalar perturbations in f(R)-cosmologies, that can be used for e

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31

Ribeiro, Ana Rita Lopes. "Covariant Effective Actions in f(R) gravity for Modified Loop Quantum Cosmologies via Order Reduction." Master's thesis, 2020. http://hdl.handle.net/10451/47688.

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Tese de mestrado, Física (Astrofísica e Cosmologia), Universidade de Lisboa, Faculdade de Ciências, 2021<br>The ɅCDM model relies upon the fact that General Relativity is the correct theory for gravity, concerning the large scales of the Universe. In fact, General Relativity is an extremely successful theory, as it was able to perfectly explain the precession of Mercury’s orbit or the gravitational deflection of light by the Sun, for example. The ɅCDM model itself is a very successful model for the Universe. Among other astrophysical and cosmological observations, it is able to explain the Cos

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32

Moraes, Bruno. "Les Mystères de l'Energie Noire." Thesis, 2010. http://www.theses.fr/2010MON20032.

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L'un des plus grands problèmes ouverts de la cosmologie moderne est l'origine de l'expansion accélérée de l'Univers, découverte en 1998. L'explication théorique la plus simple repose sur l'introduction d'une constante cosmologique $Lambda$. Ce modèle, connu sous le nom de $Lambda$CDM, est en accord avec les différentes observations liées à l'expansion accélérée. Cependant, il présente des problèmes d'ordre théorique. Par conséquent, plusieurs alternatives, connues collectivement sous le nom de {it modèles d'énergie noire}, ont été proposées pour expliquer cette accélération. Plusieurs d'entre

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33

Karamazov, Michal. "Přesné prostoročasy v modifikovaných teoriích gravitace." Master's thesis, 2017. http://www.nusl.cz/ntk/nusl-357266.

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In the review part of the thesis we summarize various modified theories of gravity, especially those that are characterized by additional curvature invariants in the Lagrangian density. Further, we review non-twisting geometries, especially their Kundt subclass. Finally, from the principle of least action we derive field equations for the case with the Lagrangian density corresponding to an arbitrary function of the curvature invariants. In the original part of the thesis we explicitly express particular components of the field equations for non-gyratonic Kundt geometry in generic quadratic gr

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