DOCSLIB.ORG

Modified Gravity and Cosmology Clifton, T; Ferreira, PG; Padilla, A; Skordis, C

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Modified Gravity and Cosmology Clifton, T; Ferreira, PG; Padilla, A; Skordis, C Modified Gravity and Cosmology Clifton, T; Ferreira, PG; Padilla, A; Skordis, C © 2012 Elsevier B.V This is a pre-copyedited, author-produced PDF of an article accepted for publication in Physics Reports following peer review. The version of record is available at http://www.sciencedirect.com/science/article/pii/S0370157312000105 For additional information about this publication click this link. http://qmro.qmul.ac.uk/xmlui/handle/123456789/17822 Information about this research object was correct at the time of download; we occasionally make corrections to records, please therefore check the published record when citing. For more information contact [email protected] Modified Gravity and Cosmology Timothy Cliftona, Pedro G. Ferreiraa, Antonio Padillab, Constantinos Skordisb aDepartment of Astrophysics, University of Oxford, UK. bSchool of Physics and Astronomy, University of Nottingham, UK. Abstract In this review we present a thoroughly comprehensive survey of recent work on modi- fied theories of gravity and their cosmological consequences. Amongst other things, we cover General Relativity, Scalar-Tensor, Einstein-Aether, and Bimetric theories, as well as TeVeS, f(R), general higher-order theories, Hoˇrava-Lifschitz gravity, Galileons, Ghost Condensates, and models of extra dimensions including Kaluza-Klein, Randall-Sundrum, DGP, and higher co-dimension braneworlds. We also review attempts to construct a Pa- rameterised Post-Friedmannian formalism, that can be used to constrain deviations from General Relativity in cosmology, and that is suitable for comparison with data on the largest scales. These subjects have been intensively studied over the past decade, largely motivated by rapid progress in the field of observational cosmology that now allows, for the first time, precision tests of fundamental physics on the scale of the observable Universe. The purpose of this review is to provide a reference tool for researchers and stu- dents in cosmology and gravitational physics, as well as a self-contained, comprehensive and up-to-date introduction to the subject as a whole. Keywords: General Relativity, Gravitational Physics, Cosmology, Modified Gravity arXiv:1106.2476v3 [astro-ph.CO] 12 Mar 2012 Preprint submitted to Physics Reports March 13, 2012 Contents 1 Introduction 5 2 General Relativity, and its Foundations 11 2.1 Requirements for Validity . 11 2.1.1 The foundations of relativistic theories . 11 2.1.2 Observational tests of metric theories of gravity . 14 2.1.3 Theoretical considerations . 20 2.2 Einstein's Theory . 22 2.2.1 The field equations . 23 2.2.2 The action . 24 2.3 Alternative Formulations . 25 2.3.1 The Palatini procedure . 25 2.3.2 Metric-affine gravity and matter . 27 2.3.3 Other approaches . 27 2.4 Theorems . 29 2.4.1 Lovelock's theorem . 29 2.4.2 Birkhoff's theorem . 30 2.4.3 The no-hair theorems . 31 2.5 The Parameterised Post-Newtonian Approach . 32 2.5.1 Parameterised post-Newtonian formalism . 32 2.5.2 Parameterised post-Newtonian constraints . 34 2.6 Cosmology . 37 2.6.1 The Friedmann-Lema^ıtre-Robertson-Walker solutions . 37 2.6.2 Cosmological distances . 38 2.6.3 Perturbation theory . 40 2.6.4 Gravitational potentials and observations . 42 2.6.5 The evidence for the ΛCDM model . 44 2.6.6 Shortcomings of the ΛCDM model . 46 3 Alternative Theories of Gravity with Extra Fields 49 3.1 Scalar-Tensor Theories . 49 3.1.1 Action, field equations, and conformal transformations . 49 3.1.2 Brans-Dicke theory . 52 3.1.3 General scalar-tensor theories . 59 3.1.4 The chameleon mechanism . 66 3.2 Einstein-Æther Theories . 68 3.2.1 Modified Newtonian dynamics . 68 3.2.2 Action and field equations . 69 3.2.3 FLRW solutions . 70 3.2.4 Cosmological perturbations . 71 3.2.5 Observations and constraints . 73 3.3 Bimetric Theories . 75 3.3.1 Rosen's theory, and non-dynamical metrics . 76 3.3.2 Drummond's theory . 77 3.3.3 Massive gravity . 77 2 3.3.4 Bigravity . 79 3.3.5 Bimetric MOND . 80 3.4 Tensor-Vector-Scalar Theories . 81 3.4.1 Actions and field equations . 82 3.4.2 Newtonian and MOND limits . 84 3.4.3 Homogeneous and isotropic cosmology . 86 3.4.4 Cosmological perturbation theory . 91 3.4.5 Cosmological observations and constraints . 93 3.5 Other Theories . 96 3.5.1 The Einstein-Cartan-Sciama-Kibble Theory . 96 3.5.2 Scalar-Tensor-Vector Theory . 99 4 Higher Derivative and Non-Local Theories of Gravity 101 4.1 f(R) Theories . 101 4.1.1 Action, field equations and transformations . 102 4.1.2 Weak-field limit . 106 4.1.3 Exact solutions, and general behaviour . 111 4.1.4 Cosmology . 114 4.1.5 Stability issues . 120 4.2 General combinations of Ricci and Riemann curvature. 123 4.2.1 Action and field equations . 123 4.2.2 Weak-field limit . 125 4.2.3 Exact solutions, and general behaviour . 126 4.2.4 Physical cosmology and dark energy . 128 4.2.5 Other topics . 131 4.3 Hoˇrava-Lifschitz Gravity . 137 4.3.1 The projectable theory . 141 4.3.2 The non-projectable theory . 144 4.3.3 Aspects of Hoˇrava-Lifschitz cosmology . 146 4.3.4 The ΘCDM model . 148 4.3.5 HMT-da Silva theory . 148 4.4 Galileons . 150 4.4.1 Galileon modification of gravity . 151 4.4.2 Covariant galileon . 157 4.4.3 DBI galileon . 158 4.4.4 Galileon cosmology . 160 4.4.5 Multi-galileons . 161 4.5 Other Theories . 164 4.5.1 Ghost condensates . 164 4.5.2 Non-metric gravity . 166 4.5.3 Dark energy from curvature corrections . 169 5 Higher Dimensional Theories of Gravity 172 5.1 Kaluza-Klein Theories of Gravity . 172 5.1.1 Kaluza-Klein compactifications . 173 5.1.2 Kaluza-Klein cosmology . 174 5.2 The Braneworld Paradigm . 179 3 5.2.1 The ADD model . 180 5.3 Randall-Sundrum Gravity . 181 5.3.1 The RS1 model . 182 5.3.2 The RS2 model . 184 5.3.3 Other RS-like models . 185 5.3.4 Action and equations of motion . 188 5.3.5 Linear perturbations in RS1 and RS2 . 189 5.4 Brane Cosmology . 195 5.4.1 Brane based formalism { covariant formulation . 197 5.4.2 Bulk based formalism { moving branes in a static bulk . 199 5.4.3 Cosmological perturbations . 200 5.5 Dvali-Gabadadze-Porrati Gravity . 207 5.5.1 Action, equations of motion, and vacua . 207 5.5.2 Linear perturbations on the normal branch . 209 5.5.3 Linear perturbations (and ghosts) on the self-accelerating branch . 211 5.5.4 From strong coupling to the Vainshtein mechanism . 214 5.5.5 DGP cosmology . 221 5.6 Higher Co-Dimension Braneworlds . 228 5.6.1 Cascading gravity . 230 5.6.2 Degravitation . 235 5.7 Einstein Gauss-Bonnet Gravity . 236 5.7.1 Action, equations of motion, and vacua . 237 5.7.2 Kaluza-Klein reduction of EGB gravity . 240 5.7.3 Co-dimension one branes in EGB gravity . 240 5.7.4 Co-dimension two branes in EGB gravity . 244 6 Parameterised Post-Friedmannian Approaches and Observational Con- straints 246 6.1 The Formalism . 247 6.1.1 Evolution of perturbations on super-horizon scales . 248 6.1.2 The simplified PPF approach, and its extensions . 249 6.1.3 The Hu-Sawicki frame-work . 253 6.2 Models for µ and ζ on Sub-Horizon Scales . 254 6.2.1 The importance of shear . 254 6.2.2 The growth function . 255 6.2.3 Current constraints on the PPF parameters . 257 6.2.4 Constraining the growth rate . 258 6.2.5.
Load more

Recommended publications
  • Variational Problem and Bigravity Nature of Modified Teleparallel Theories
    Variational Problem and Bigravity Nature of Modified Teleparallel Theories Martin Krˇsˇs´ak∗ Institute of Physics, University of Tartu, W. Ostwaldi 1, Tartu 50411, Estonia August 15, 2017 Abstract We consider the variational principle in the covariant formulation of modified telepar- allel theories with second order field equations. We vary the action with respect to the spin connection and obtain a consistency condition relating the spin connection with the tetrad. We argue that since the spin connection can be calculated using an additional reference tetrad, modified teleparallel theories can be interpreted as effectively bigravity theories. We conclude with discussion about the relation of our results and those obtained in the usual, non-covariant, formulation of teleparallel theories and present the solution to the problem of choosing the tetrad in f(T ) gravity theories. 1 Introduction Teleparallel gravity is an alternative formulation of general relativity that can be traced back to Einstein’s attempt to formulate the unified field theory [1–9]. Over the last decade, various modifications of teleparallel gravity became a popular tool to address the problem of the accelerated expansion of the Universe without invoking the dark sector [10–38]. The attractiveness of modifying teleparallel gravity–rather than the usual general relativity–lies in the fact that we obtain an entirely new class of modified gravity theories, which have second arXiv:1705.01072v3 [gr-qc] 13 Aug 2017 order field equations. See [39] for the extensive review. A well-known shortcoming of the original formulation of teleparallel theories is the prob- lem of local Lorentz symmetry violation [40, 41].
    [Show full text]
  • A Critique of Covariant Emergent Gravity
    Prepared for submission to JCAP A Critique of Covariant Emergent Gravity Kirill Zatrimaylov Scuola Normale Superiore and I.N.F.N. Piazza dei Cavalieri 7, 56126, Pisa, Italy E-mail: [email protected] Abstract. I address some problems encountered in the formulation of relativistic models encompassing the MOND phenomenology of radial acceleration. I explore scalar and vector theories with fractional kinetic terms and f(R)-type gravity, demanding that the energy density be bounded from below and that superluminal modes be absent, but also that some consistency constraints with observational results hold. I identify configurations whose energy is unbounded from below and formulate some no-go statements for vector field models and arXiv:2003.10410v1 [gr-qc] 23 Mar 2020 modified gravity theories. Finally, I discuss superfluid dark matter as a hybrid theory lying between CDM and modified gravity, highlighting some difficulties present also in this case, which appears preferable to the others. Contents 1 Introduction1 2 A Brief Overview of MOND3 3 Covariant Theories with Fractional Kinetic Terms6 3.1 Scalar 8 3.2 Vector 9 3.3 Tensor 15 4 Fractional Kinetic Terms from Spontaneous Symmetry Breaking 19 5 Conclusions 20 1 Introduction MOND (Modified Newtonian dynamics), proposed by M. Milgrom in 1981 [1], was meant originally as an alternative to the cold dark matter paradigm: it aims to explain phenomena usually attributed to dark matter via Newtonian laws (either the law of gravity or the law of inertia) that are modified at large distances and small accelerations. Until recently, its actual significance has been somewhat obscure, since it does account for one class of observations (galaxy rotation curves) without addressing other key issues (CMB, primordial structure formation, and displacement between luminous and dark matter components in galaxy cluster collisions).
    [Show full text]
  • The Emergence of Gravitational Wave Science: 100 Years of Development of Mathematical Theory, Detectors, Numerical Algorithms, and Data Analysis Tools
    BULLETIN (New Series) OF THE AMERICAN MATHEMATICAL SOCIETY Volume 53, Number 4, October 2016, Pages 513–554 http://dx.doi.org/10.1090/bull/1544 Article electronically published on August 2, 2016 THE EMERGENCE OF GRAVITATIONAL WAVE SCIENCE: 100 YEARS OF DEVELOPMENT OF MATHEMATICAL THEORY, DETECTORS, NUMERICAL ALGORITHMS, AND DATA ANALYSIS TOOLS MICHAEL HOLST, OLIVIER SARBACH, MANUEL TIGLIO, AND MICHELE VALLISNERI In memory of Sergio Dain Abstract. On September 14, 2015, the newly upgraded Laser Interferometer Gravitational-wave Observatory (LIGO) recorded a loud gravitational-wave (GW) signal, emitted a billion light-years away by a coalescing binary of two stellar-mass black holes. The detection was announced in February 2016, in time for the hundredth anniversary of Einstein’s prediction of GWs within the theory of general relativity (GR). The signal represents the first direct detec- tion of GWs, the first observation of a black-hole binary, and the first test of GR in its strong-field, high-velocity, nonlinear regime. In the remainder of its first observing run, LIGO observed two more signals from black-hole bina- ries, one moderately loud, another at the boundary of statistical significance. The detections mark the end of a decades-long quest and the beginning of GW astronomy: finally, we are able to probe the unseen, electromagnetically dark Universe by listening to it. In this article, we present a short historical overview of GW science: this young discipline combines GR, arguably the crowning achievement of classical physics, with record-setting, ultra-low-noise laser interferometry, and with some of the most powerful developments in the theory of differential geometry, partial differential equations, high-performance computation, numerical analysis, signal processing, statistical inference, and data science.
    [Show full text]
  • 18Th Annual Student Research and Creativity Celebration at Buffalo State College
    III IIII II I I I I I I I I III IIII II I I I I I I I I Editor Jill Singer, Ph.D. Director, Office of Undergraduate Research Cover Design and Layout: Carol Alex The following individuals and offices are acknowledged for their many contributions: Marc Bayer, Interim Library Director, E.H. Butler Library, Department and Program Coordinators (identified below) and the library staff Donald Schmitter, Hospitality and Tourism, and students and very special thanks to: in HTR 400: Catering Management Kaylene Waite, Graphic Design, Instructional Resources Bruce Fox, Photographer Carol Alex, Center for Development of Human Services Andrew Chambers, Information Management Officer Sean Fox, Ellofex, Inc. Bernadette Gilliam and Mary Beth Wojtaszek, Events Management Department and Program Coordinators for the Eighteenth Annual Student Research and Creativity Celebration Lisa Marie Anselmi, Anthropology Dan MacIsaac, Physics Sarbani Banerjee, Computer Information Systems Candace Masters, Art Education Saziye Bayram, Mathematics Carmen McCallum, Higher Education Administration Carol Beckley, Theater Michaelene Meger, Exceptional Education Lynn Boorady, Fashion and Textile Technology Andrew Nicholls, History and Social Studies Education Louis Colca, Social Work Jill Norvilitis, Psychology Sandra Washington-Copeland, McNair Scholars Program Kathleen O’Brien, Hospitality and Tourism Carol DeNysschen, Health, Nutrition, and Dietetics Lorna Perez, English Eric Dolph, Interior Design Rebecca Ploeger, Art Conservation Reva Fish, Social & Psychological Foundations
    [Show full text]
  • Non-Inflationary Bianchi Type VI0 Model in Rosen's Bimetric Gravity
    Applications and Applied Mathematics: An International Journal (AAM) Volume 11 Issue 2 Article 25 12-2016 Non-Inflationary Bianchi Type VI0 Model in Rosen’s Bimetric Gravity M. S. Borkar R. T. M. Nagpur University N. P. Gaikwad Dharampeth M. P. Deo Memorial Science College Follow this and additional works at: https://digitalcommons.pvamu.edu/aam Part of the Other Physics Commons Recommended Citation Borkar, M. S. and Gaikwad, N. P. (2016). Non-Inflationary Bianchi Type VI0 Model in Rosen’s Bimetric Gravity, Applications and Applied Mathematics: An International Journal (AAM), Vol. 11, Iss. 2, Article 25. Available at: https://digitalcommons.pvamu.edu/aam/vol11/iss2/25 This Article is brought to you for free and open access by Digital Commons @PVAMU. It has been accepted for inclusion in Applications and Applied Mathematics: An International Journal (AAM) by an authorized editor of Digital Commons @PVAMU. For more information, please contact [email protected]. Borkar and Gaikwad: Bianchi Type VI0 Model in Rosen’s Bimetric Gravity Available at http://pvamu.edu/aam Applications and Applied Appl. Appl. Math. Mathematics: ISSN: 1932-9466 An International Journal (AAM) Vol. 11, Issue 2 (December 2016), pp. 875 - 887 Non-Inflationary Bianchi Type VI0 Model in Rosen’s Bimetric Gravity M. S. Borkar1 and N. P. Gaikwad2 1Post Graduate Department of Mathematics R. T. M. Nagpur University Nagpur – 440 033, India E–mail : [email protected] 2Department of Mathematics Dharampeth M. P. Deo Memorial Science College Nagpur – 440 033, India E-mail : [email protected] Received: March 19, 2015; Accepted: July 7, 2016 Abstract In this paper, we have present the solution of Bianchi type VI0 space-time by solving the Rosen’s field equations with massless scalar field and with constant scalar potential V for flat region.
    [Show full text]
  • Kinetic Models for the in Situ Reaction Between Cu-Ti Melt and Graphite
    metals Article Kinetic Models for the in Situ Reaction between Cu-Ti Melt and Graphite Lei Guo, Xiaochun Wen and Zhancheng Guo * State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Xueyuan Road No.30, Haidian District, Beijing 100083, China; [email protected] (L.G.); [email protected] (X.W.) * Correspondence: [email protected]; Tel.: +86-135-2244-2020 Received: 16 January 2020; Accepted: 17 February 2020; Published: 18 February 2020 Abstract: The in situ reaction method for preparing metal matrix composites has the advantages of a simple process, good combination of the reinforcing phase and matrix, etc. Based on the mechanism of forming TiCx particles via the dissolution reaction of solid carbon (C) particles in Cu-Ti melt, the kinetic models for C particle dissolution reaction were established. The kinetic models of the dissolution reaction of spherical, cylindrical, and flat C source particles in Cu-Ti melt were deduced, and the expressions of the time for the complete reaction of C source particles of different sizes were obtained. The mathematical relationship between the degree of reaction of C source and the reaction time was deduced by introducing the shape factor. By immersing a cylindrical C rod in a Cu-Ti melt and placing it in a super-gravity field for the dissolution reaction, it was found that the super-gravity field could cause the precipitated TiCx particles to aggregate toward the upper part of the sample under the action of buoyancy. Therefore, the consuming rate of the C rod was significantly accelerated. Based on the flat C source reaction kinetic model, the relationship between the floating speed of TiCx particles in the Cu-Ti melt and the centrifugal velocity (or the coefficient of super-gravity G) was derived.
    [Show full text]
  • Modified Newtonian Dynamics
    Faculty of Mathematics and Natural Sciences Bachelor Thesis University of Groningen Modified Newtonian Dynamics (MOND) and a Possible Microscopic Description Author: Supervisor: L.M. Mooiweer prof. dr. E. Pallante Abstract Nowadays, the mass discrepancy in the universe is often interpreted within the paradigm of Cold Dark Matter (CDM) while other possibilities are not excluded. The main idea of this thesis is to develop a better theoretical understanding of the hidden mass problem within the paradigm of Modified Newtonian Dynamics (MOND). Several phenomenological aspects of MOND will be discussed and we will consider a possible microscopic description based on quantum statistics on the holographic screen which can reproduce the MOND phenomenology. July 10, 2015 Contents 1 Introduction 3 1.1 The Problem of the Hidden Mass . .3 2 Modified Newtonian Dynamics6 2.1 The Acceleration Constant a0 .................................7 2.2 MOND Phenomenology . .8 2.2.1 The Tully-Fischer and Jackson-Faber relation . .9 2.2.2 The external field effect . 10 2.3 The Non-Relativistic Field Formulation . 11 2.3.1 Conservation of energy . 11 2.3.2 A quadratic Lagrangian formalism (AQUAL) . 12 2.4 The Relativistic Field Formulation . 13 2.5 MOND Difficulties . 13 3 A Possible Microscopic Description of MOND 16 3.1 The Holographic Principle . 16 3.2 Emergent Gravity as an Entropic Force . 16 3.2.1 The connection between the bulk and the surface . 18 3.3 Quantum Statistical Description on the Holographic Screen . 19 3.3.1 Two dimensional quantum gases . 19 3.3.2 The connection with the deep MOND limit .
    [Show full text]
  • Analytical Constraints on Bimetric Gravity
    Prepared for submission to JCAP Analytical constraints on bimetric gravity Marcus H¨og˚as,Edvard M¨ortsell The Oskar Klein Centre, Department of Physics, Stockholm University, SE 106 91, Stock- holm, Sweden E-mail: [email protected], [email protected] Abstract. Ghost-free bimetric gravity is an extension of general relativity, featuring a mas- sive spin-2 field coupled to gravity. We parameterize the theory with a set of observables having specific physical interpretations. For the background cosmology and the static, spher- ically symmetric solutions (for example approximating the gravitational potential of the solar system), there are four directions in the parameter space in which general relativity is ap- proached. Requiring that there is a working screening mechanism and a nonsingular evolution of the Universe, we place analytical constraints on the parameter space which rule out many of the models studied in the literature. Cosmological solutions where the accelerated expan- sion of the Universe is explained by the dynamical interaction of the massive spin-2 field rather than by a cosmological constant, are still viable. arXiv:2101.08794v2 [gr-qc] 10 May 2021 Contents 1 Introduction and summary1 2 Bimetric gravity3 3 Physical parameterization4 4 Local solutions6 4.1 Linearized solutions6 4.2 Vainsthein screening8 5 Background cosmology 11 5.1 Infinite branch (inconsistent) 13 5.2 Finite branch (consistent) 13 6 General relativity limits 15 6.1 Local solutions 15 6.2 Background cosmology 16 7 Constraints on the physical parameters 19 7.1 Local solutions 19 7.2 Background cosmology 20 8 Discussion and outlook 23 A List of constraints 25 B The St¨uckelberg field 26 C Constraints from the dynamical Higuchi bound 26 D Expansions 28 D.1 Around the final de Sitter point 28 D.2 mFP ! 1 limit 29 D.3 α ! 1 limit 30 D.4 β ! 1 limit 31 E Avoiding the Big Rip 32 1 Introduction and summary There are strong motivations to look for new theories of gravity, for example the unknown nature of dark matter and dark energy.
    [Show full text]
  • Dark Matter, Infinite Statistics, and Quantum Gravity Chiu Man Ho, Djordje Minic, and Y
    This is the accepted manuscript made available via CHORUS, the article has been published as: Dark matter, infinite statistics, and quantum gravity Chiu Man Ho, Djordje Minic, and Y. Jack Ng Phys. Rev. D 85, 104033 — Published 21 May 2012 DOI: 10.1103/PhysRevD.85.104033 Dark Matter, Infinite Statistics and Quantum Gravity Chiu Man Ho1∗, Djordje Minic2†, and Y. Jack Ng3‡ 1Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, U.S.A. 2Department of Physics, Virginia Tech, Blacksburg, VA 24061, U.S.A. 3Institute of Field Physics, Department of Physics and Astronomy, University of North Carolina, Chapel Hill, NC 27599, U.S.A. Abstract We elaborate on our proposal regarding a connection between global physics and local galactic dynamics via quantum gravity. This proposal calls for the concept of MONDian dark matter which behaves like cold dark matter at cluster and cosmological scales but emulates modified Newtonian dynamics (MOND) at the galactic scale. In the present paper, we first point out a surprising connection between the MONDian dark matter and an effective gravitational Born-Infeld theory. We then argue that these unconventional quanta of MONDian dark matter must obey infinite statistics, and the theory must be fundamentally non-local. Finally, we provide a possible top- down approach to our proposal from the Matrix theory point of view. PACS Numbers: 95.35.+d; 04.50.Kd; 05.30.-d; 04.60.-m ∗[email protected] †[email protected] ‡[email protected] 1 1 Introduction The fascinating problem of “missing mass”, or dark matter [1], has been historically iden- tified on the level of galaxies.
    [Show full text]
  • Cosmology Beyond Einstein Essay
    Adam R. Solomon Department of Physics, 5000 Forbes Avenue, Pittsburgh, PA 15213 email: [email protected] web: http://andrew.cmu.edu/~adamsolo/ RESEARCH INTERESTS Theoretical cosmology: dark energy, dark matter, inflation, baryogenesis; field theory; modified gravity; cosmological tests. EMPLOYMENT HISTORY Sep. 2018- Carnegie Mellon University present Postdoctoral Research Associate Department of Physics and McWilliams Center for Cosmology Sep. 2015- University of Pennsylvania Aug. 2018 Postdoctoral Fellow Center for Particle Cosmology Apr. 2015- University of Heidelberg Jul. 2015 DAAD Visiting Fellow Institute for Theoretical Physics Dec. 2014- University of Cambridge Feb. 2015 Research Assistant Department of Applied Mathematics and Theoretical Physics EDUCATION 2011-2015 University of Cambridge – Ph.D. Department of Applied Mathematics and Theoretical Physics Thesis: Cosmology Beyond Einstein Supervisor: Prof. John D. Barrow 2010-2011 University of Cambridge – Master of Advanced Study in Mathematics Part III of the Mathematical Tripos (Distinction) Essay: Probing the Very Early Universe with the Stochastic Gravitational Wave Background Supervisors: Prof. Paul Shellard, Dr. Eugene Lim 2006-2010 Yale University – B.S. in Astronomy and Physics Thesis: The Sunyaev-Zel’dovich Effect in the Wilkinson Microwave Anisotropy Probe Data Supervisors: Prof. Daisuke Nagai, Dr. Suchetana Chatterjee PUBLICATIONS AND CONFERENCE PROCEEDINGS 1. Khoury, J., Sakstein, J., & Solomon, A. R., “Superfluids and the Cosmological Constant Problem.” 2018, JCAP08(2018)024, arXiv:1805.05937 2. Solomon, A. R. & Trodden, M., “Higher-derivative operators and effective field theory for general scalar-tensor theories.” 2017, JCAP02(2018)031, arXiv:1709.09695 3. Sakstein, J. & Solomon, A. R., “Baryogenesis in Lorentz-violating gravity theories.” 2017, Phys. Lett. B 773, 186, arXiv:1705.10695 4.
    [Show full text]
  • Broken Scale Invariance, Gravity Mass, and Dark Energy in Modified Einstein Gravity with Two Measure Finsler Like Variables
    universe Article Broken Scale Invariance, Gravity Mass, and Dark Energy in Modified Einstein Gravity with Two Measure Finsler like Variables Panayiotis Stavrinos 1 and Sergiu I. Vacaru 2,3,*,† 1 Department of Mathematics, National and Kapodistrian University of Athens, 1584 Athens, Greece; [email protected] 2 Physics Department, California State University at Fresno, Fresno, CA 93740, USA 3 Department of Theoretical Physics and Computer Modelling, Yu. Fedkovych Chernivtsi National University, 101 Storozhynetska Street, 58029 Chernivtsi, Ukraine * Correspondence: [email protected] † Current address: Correspondence in 2021 as a Visiting Researcher at YF CNU Ukraine: Yu. Gagarin Street, nr. 37/3, 58008 Chernivtsi, Ukraine. Abstract: We study new classes of generic off-diagonal and diagonal cosmological solutions for effective Einstein equations in modified gravity theories (MGTs), with modified dispersion relations (MDRs), and encoding possible violations of (local) Lorentz invariance (LIVs). Such MGTs are constructed for actions and Lagrange densities with two non-Riemannian volume forms (similar to two measure theories (TMTs)) and associated bimetric and/or biconnection geometric structures. For conventional nonholonomic 2 + 2 splitting, we can always describe such models in Finsler-like variables, which is important for elaborating geometric methods of constructing exact and para- metric solutions. Examples of such Finsler two-measure formulations of general relativity (GR) and MGTs are considered for Lorentz manifolds and their (co) tangent bundles and abbreviated as Citation: Stavrinos, P.; Vacaru, S.I. FTMT. Generic off-diagonal metrics solving gravitational field equations in FTMTs are determined by Broken Scale Invariance, Gravity generating functions, effective sources and integration constants, and characterized by nonholonomic Mass, and Dark Energy in frame torsion effects.
    [Show full text]
  • Teleparallel Gravity and Its Modifications
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by UCL Discovery University College London Department of Mathematics PhD Thesis Teleparallel gravity and its modifications Author: Supervisor: Matthew Aaron Wright Christian G. B¨ohmer Thesis submitted in fulfilment of the requirements for the degree of PhD in Mathematics February 12, 2017 Disclaimer I, Matthew Aaron Wright, confirm that the work presented in this thesis, titled \Teleparallel gravity and its modifications”, is my own. Parts of this thesis are based on published work with co-authors Christian B¨ohmerand Sebastian Bahamonde in the following papers: • \Modified teleparallel theories of gravity", Sebastian Bahamonde, Christian B¨ohmerand Matthew Wright, Phys. Rev. D 92 (2015) 10, 104042, • \Teleparallel quintessence with a nonminimal coupling to a boundary term", Sebastian Bahamonde and Matthew Wright, Phys. Rev. D 92 (2015) 084034, • \Conformal transformations in modified teleparallel theories of gravity revis- ited", Matthew Wright, Phys.Rev. D 93 (2016) 10, 103002. These are cited as [1], [2], [3] respectively in the bibliography, and have been included as appendices. Where information has been derived from other sources, I confirm that this has been indicated in the thesis. Signed: Date: i Abstract The teleparallel equivalent of general relativity is an intriguing alternative formula- tion of general relativity. In this thesis, we examine theories of teleparallel gravity in detail, and explore their relation to a whole spectrum of alternative gravitational models, discussing their position within the hierarchy of Metric Affine Gravity mod- els. Consideration of alternative gravity models is motivated by a discussion of some of the problems of modern day cosmology, with a particular focus on the dark en- ergy problem.
    [Show full text]