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Modified Gravity and Cosmology
, 2012
"... In this review we present a thoroughly comprehensive survey of recent work on modified theories of gravity and their cosmological consequences. Amongst other things, we cover General Relativity, ScalarTensor, EinsteinAether, and Bimetric theories, as well as TeVeS, f(R), general higherorder theo ..."
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In this review we present a thoroughly comprehensive survey of recent work on modified theories of gravity and their cosmological consequences. Amongst other things, we cover General Relativity, ScalarTensor, EinsteinAether, and Bimetric theories, as well as TeVeS, f(R), general higherorder theories, HořavaLifschitz gravity, Galileons, Ghost Condensates, and models of extra dimensions including KaluzaKlein, RandallSundrum, DGP, and higher codimension braneworlds. We also review attempts to construct a Parameterised PostFriedmannian 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 students in cosmology and gravitational physics, as well as a selfcontained, comprehensive and uptodate introduction to the subject as a whole.
Categorizing different approaches to the cosmological constant problem
"... Abstract. We have found that proposals addressing the old cosmological constant problem come in various categories. The aim of this paper is to identify as many different, credible mechanisms as possible and to provide them with a code for future reference. We find that they all can be classified in ..."
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Abstract. We have found that proposals addressing the old cosmological constant problem come in various categories. The aim of this paper is to identify as many different, credible mechanisms as possible and to provide them with a code for future reference. We find that they all can be classified into five different schemes of which we indicate the advantages and drawbacks. Besides, we add a new approach based on a symmetry principle mapping real to
Solar system effects in Schwarzschild–de Sitter space–time
 Phys. Lett
"... The Schwarzschild–de Sitter space–time describes the gravitational field of a spherically symmetric mass in a universe with cosmological constant Λ. Based on this space–time we calculate Solar system effects like gravitational redshift, light deflection, gravitational time delay, Perihelion shift, g ..."
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The Schwarzschild–de Sitter space–time describes the gravitational field of a spherically symmetric mass in a universe with cosmological constant Λ. Based on this space–time we calculate Solar system effects like gravitational redshift, light deflection, gravitational time delay, Perihelion shift, geodetic or de Sitter precession, as well as the influence of Λ on a Doppler measurement, used to determine the velocity of the Pioneer 10 and 11 spacecraft. For Λ = Λ0 ∼ 10 −52 m −2 the cosmological constant plays no role for all of these effects, while a value of Λ ∼ −10 −37 m −2, if hypothetically held responsible for the Pioneer anomaly, is not compatible with the Perihelion shift. 1
Cosmic Mimicry: Is LCDM a Braneworld in disguise ? astroph/0505004
"... Abstract. For a broad range of parameter values, braneworld models display a remarkable property which we call cosmic mimicry. Cosmic mimicry is characterized by the fact that, at low redshifts, the Hubble parameter in the braneworld model is virtually indistinguishable from that in the LCDM (Λ + Co ..."
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Abstract. For a broad range of parameter values, braneworld models display a remarkable property which we call cosmic mimicry. Cosmic mimicry is characterized by the fact that, at low redshifts, the Hubble parameter in the braneworld model is virtually indistinguishable from that in the LCDM (Λ + Cold Dark Matter) cosmology. An important point to note is that the Ωm parameters in the braneworld model and in the LCDM cosmology can nevertheless be quite different. Thus, at high redshifts (early times), the braneworld asymptotically expands like a matterdominated universe with the value of Ωm inferred from the observations of the local matter density. At low redshifts (late times), the braneworld model behaves almost exactly like the LCDM model but with a renormalized value of the cosmological density parameter ΩLCDM m. is smaller (larger) than Ωm in the braneworld model with positive (negative) brane tension. The redshift which characterizes cosmic mimicry is related to the parameters in the higherdimensional braneworld Lagrangian. Cosmic mimicry is a natural consequence of the scaledependence of gravity in braneworld models. The change in the value of the cosmological density parameter (from Ωm at high z The value of Ω LCDM m at low z) is shown to be related to the spatial dependence of the effective gravitational constant Geff in braneworld theory. A subclass of mimicry models lead to an older age of the universe and also predict a redshift of reionization which is lower than zreion ≃ 17 in the LCDM cosmology. These models might therefore provide a background cosmology which is in better agreement both with the observed quasar abundance at z> ∼ 4 and with the large optical depth to reionization measured by the
Solar system planetary motion and modified gravity,” grqc/0511138
, 2005
"... According to the braneworld model of gravity by Dvali, Gabadadze and Porrati, our Universe is a fourdimensional spacetime brane embedded in a larger, infinite fivedimensional bulk space. Contrary to the other forces constrained to remain on the brane, gravity is able to explore the entire bulk ge ..."
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According to the braneworld model of gravity by Dvali, Gabadadze and Porrati, our Universe is a fourdimensional spacetime brane embedded in a larger, infinite fivedimensional bulk space. Contrary to the other forces constrained to remain on the brane, gravity is able to explore the entire bulk getting substantially modified at large distances. This model has not only cosmological consequences allowing to explain the observed acceleration of the expansion of our Universe without resorting to the concept of dark energy, but makes also testable predictions at small scales. Interestingly, such local effects can yield information on the global properties of the Universe and on the kind of expansion currently ongoing. Indeed, among such predictions there are extra precessions of the perihelia and the mean longitudes of the planetary orbits which are affected by a twofold degeneration sign: one sign refers to a FriedmannLemaîtreRobertsonWalker phase while the opposite sign is for a selfsccelerated phase. In this paper we report on recent observations of planetary motions in the Solar System which are compatible with the existence of a fifth dimension as predicted in the DvaliGabadadzePorrati model with a selfaccelerated cosmological phase, although the errors are still large. The FriedmannLemaître
Beyond the Cosmological Standard Model
, 2014
"... After a decade and a half of research motivated by the accelerating universe, theory and experiment have a reached a certain level of maturity. The development of theoretical models beyond Λ or smooth dark energy, often called modified gravity, has led to broader insights into a path forward, and a ..."
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After a decade and a half of research motivated by the accelerating universe, theory and experiment have a reached a certain level of maturity. The development of theoretical models beyond Λ or smooth dark energy, often called modified gravity, has led to broader insights into a path forward, and a host of observational and experimental tests have been developed. In this review we present the current state of the field and describe a framework for anticipating developments in the next decade. We identify the guiding principles for rigorous and consistent modifications of the standard model, and discuss the prospects for empirical tests. We begin by reviewing recent attempts to consistently modify Einstein gravity in the infrared, focusing on the notion that additional degrees of freedom introduced by the modification must “screen” themselves from local tests of gravity. We categorize screening mechanisms into three broad classes: mechanisms which become active in regions of high Newtonian potential, those in which first derivatives of the field become important, and those for which second derivatives of the field are important. Examples of the first class, such as f(R) gravity, employ the familiar chameleon or symmetron mechanisms, whereas examples of the last class are galileon
Theoretical Models of Dark Energy
 Int.J.Mod.Phys
"... Mounting observational data confirm that about 73 % of the energy density consists of dark energy which is responsible for the current accelerated expansion of the Universe. We present observational evidences and dark energy projects. We then review various theoretical ideas that have been proposed ..."
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Mounting observational data confirm that about 73 % of the energy density consists of dark energy which is responsible for the current accelerated expansion of the Universe. We present observational evidences and dark energy projects. We then review various theoretical ideas that have been proposed to explain the origin of dark energy; they contain the cosmological constant, modified matter models, modified gravity models and the inhomogeneous model. The cosmological constant suffers from two major problems: one regarding finetuning and the other regarding coincidence. To solve them there arose modified matter models such as quintessence, kessence, coupled dark energy, and unified dark energy. We compare those models by presenting attractive aspects, new rising problems and possible solutions. Furthermore we review modified gravity models that lead to latetime accelerated expansion without invoking a new form of dark energy; they contain f(R) gravity and the DvaliGabadadzePorrati model. We also discuss observational constraints on those models and on future modified gravity theories. Finally we review the inhomogeneous LemâıtreTolmanBondi model that drops an assumption of the spatial homogeneity of the Universe. We also present basics of cosmology and scalar field theory, which are useful especially for students and novices to understand dark energy models. 1 jaewon.yoo ‘at ’ physik.unimuenchen.de 2 watanabe ‘at ’ resceu.s.utokyo.ac.jp ar
How the orbital period of a test particle is modified by the DvaliGabadadzePorrati gravity?
, 2008
"... periods In addition to the pericentre ω, the mean anomaly M and, thus, the mean longitude λ, also the orbital period Pb and the mean motion n of a test particle are modified by the DvaliGabadadzePorrati gravity. While the correction to Pb depends on the mass of the central body and on the geometri ..."
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periods In addition to the pericentre ω, the mean anomaly M and, thus, the mean longitude λ, also the orbital period Pb and the mean motion n of a test particle are modified by the DvaliGabadadzePorrati gravity. While the correction to Pb depends on the mass of the central body and on the geometrical features of the orbital motion around it, the correction to n is independent of them, up to terms of second order in the eccentricity e. The latter one amounts to about 2 × 10 −3 arcseconds per century. The presentday accuracy in determining the mean motions of the inner planets of the Solar System from radar ranging and differential Very Long Baseline Interferometry (∆VLBI) is 10 −2 − 5 × 10 −3 arcseconds per century, but it should be improved According to the DvaliGabadadzePorrati (DGP) model of gravity [1], our Universe is a (3+1) spacetime brane embedded in a fivedimensional Minkowskian bulk with an extraspatial dimension which is flat and infinite. Many important consequences of cosmological interest, mainly related to the observed cosmic acceleration, can be traced out from such