Cosmological dynamics and dark energy from nonlocal infrared modifications of gravity

Foffa, Stefano; Maggiore, Michele; Mitsou, Ermis

doi:10.1142/s0217751x14501164

Cited by 72 publications

(121 citation statements)

References 79 publications

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“…2.4). For example, a series of papers [189,148,149,190,49] has explored the viability -both theoretical and observational -of introducing non-local terms to the gravitational field equations, e.g. ∼ m 2 g µν −1 R T , where −1 is the inverse d'Alembertian, and R is the Ricci scalar (see also Refs.…”

Section: Gravity In Cosmologymentioning

confidence: 99%

BeyondΛCDM: Problems, solutions, and the road ahead

Bull

Akrami

Adamek

et al. 2016

Physics of the Dark Universe

460

210

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Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, ΛCDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. In this paper, we summarize the current status of ΛCDM as a physical theory, and review investigations into possible alternatives along a number of different lines, with a particular focus on highlighting the most promising directions. While the fundamental problems are proving reluctant to yield, the study of alternative cosmologies has led to considerable progress, with much more to come if hopes about forthcoming high-precision observations and new theoretical ideas are fulfilled.Keywords: cosmology -dark energy -cosmological constant problem -modified gravitydark matter -early universe Cosmology has been both blessed and cursed by the establishment of a standard model: ΛCDM. On the one hand, the model has turned out to be extremely predictive, explanatory, and observationally robust, providing us with a substantial understanding of the formation of large-scale structure, the state of the early Universe, and the cosmic abundance of different types of matter and energy. It has also survived an impressive battery of precision observational tests -anomalies are few and far between, and their significance is contentious where they do arise -and its predictions are continually being vindicated through the discovery of new effects (B-mode polarization [1] and lensing [2,3] of the cosmic microwave background (CMB), and the kinetic Sunyaev-Zel'dovich effect [4] being some recent examples). These are the hallmarks of a good and valuable physical theory.On the other hand, the model suffers from profound theoretical difficulties. The two largest contributions to the energy content at late times -cold dark matter (CDM) and the cosmological constant (Λ) -have entirely mysterious physical origins. CDM has so far evaded direct detection by laboratory experiments, and so the particle field responsible for it -presumably a manifestation of "beyond the standard model" particle physics -is unknown. Curious discrepancies also appear to exist between the predicted clustering properties of CDM on small scales and observations. The cosmological constant is even more puzzling, giving rise to quite simply the biggest problem in all of fundamental physics: the question of why Λ appears to take such an unnatural value [5,6,7]. Inflation, the theory of the very early Universe, has also been criticized for being fine-tuned and under-predictive [8], and appears to leave many problems either unsolved or fundamentally unresolvable. These problems are indicative of a crisis.From January 14th-17th 2015, we held a conference in Oslo, Norway to surve...

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Section: Gravity In Cosmologymentioning

confidence: 99%

BeyondΛCDM: Problems, solutions, and the road ahead

Bull

Akrami

Adamek

et al. 2016

Physics of the Dark Universe

460

210

View full text Add to dashboard Cite

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“…The corresponding cosmology not being viable, we proceeded with the study of non-local modified gravity models that are still controlled by a fixed mass parameter, but in which the graviton remains massless [70,71]. These theories contain ghost modes, i.e.…”

Section: Non-local Gravitymentioning

confidence: 99%

“…This chapter is based on, and extends, [68,70,71] Manipulating −1 on curved space-time Now −1 is a right-inverse of ≡ ∇ µ ∇ µ and therefore depends on the metric field g µν . For the reader who is interested in the mathematical details of this operator on curved space-time we suggest a first look at the appendix A.…”

Section: Non-local Gravitymentioning

confidence: 99%

Infrared Non-local Modifications of General Relativity

Mitsou¹

2016

Springer Theses

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Le sujet de recherche abordé dans cette thèse concerne le problème de l'énergie sombre en cosmologie, cette forme d'énergie encore non-identifiée qui domine actuellement la dynamique de notre univers. Nous considérons l'éventualité que ce soit une modification non-locale de la théorie de la Relativité Générale qui soità l'origine de cet effet. Inspirés par la théorie de gravité massive, nous construisons des théories non-locales dans lesquelles la gravité peut avoir une masse mais où l'invariance sous difféomorphismes n'est pas brisée. Nous nous focalisons sur la cosmologie de ces théories et les confrontonsà certaines contraintes observationnelles. Sur un plan plus théorique, nous nous attardonségalement sur les subtilités de la théorie des champs non-locale, en clarifiant certains malentendus sur la question de stabilité. RésuméDans cette thèse, notre première motivation est de construire une théorie de gravité massive qui soit invariante sous transformations de coordonnées et ne fasse pas appelà une métrique extérieure de référence, ce qui est possible si l'on a recoursà des termes non-locaux. Cependant, les contraintes phénoménologiques nous mènerontà des modifications non-locales de la Relativité Générale dans lesquselles la gravité n'est pas forcément massive, mais où la cosmologie reproduit les observations actuelles.La structure dynamique d'une théorie des champs non-locale présente quelques subtilités par rapport aux théories locales, et ne pas en tenir compte peut nous menerà conclusions erronées. Nous commençons donc par l'étude de la dynamique des théories de jauge massives, linéaires et locales, sous plusieurs angles différents, afin de mettre en avant les propriétés qui ne seront pas exportables dans le cas non-local. Nous en profitons pour discuter un aspect intéressant de la théorie linéaire d'un champ massif de spin-2, qui consiste en une symétrie de jauge cachée dans le secteur scalaire. Elle n'apparaît que lorsque les champs non-dynamiques sontéliminésà travers leuréquations du mouvement et, en ce sens, elle correspondà une symétrie de la physique, mais pasà une symétrie de l'action.Nous terminons l'étude des théories massives locales linéaires en les reformulant en tant que théories massives non-locales mais invariantes de jauge,à travers le formalisme de Stückelberg. Ceci constitue notre premier pas dans les théories non-locales, même si en l'occurrence la non-localité n'est qu'apparante et disparaît avec un choix de jauge approprié. Cependant, la technologie ainsi développée nous permet de définir une théorie d'un champ spin-2 massif linaire réellement non-locale et invariante de jauge.Suiteà cela nous faisons une pause pour discuter en profondeur les subtilités des théories non-locales susmentionnées. La première est que deséquations non-locales et causales ne peuvent pasêtre obtenuesà travers le principe variationnel standard appliquéà une action non-locale, mais qu'il existe cependant un principe variationnel plus général qui fait l'affaire. Ensuite,à travers un processus de loca...

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“…So here we can only perturb the d 2 − d − 2 independent initial conditions ofg µν . Therefore, the 17 Note that the canonical normalization for ϕ unfortunately makes sense only for m = 0. If we want to keep track of the m → 0 limit to GR, then we should rather use something like Φ := M e mϕ M 2 , so that for m → 0 we get Φ → M .…”

Section: Stabilitymentioning

confidence: 99%

“…where ρ, p are the effective energy density and pressure, respectively 24 . As shown in [17], ζ and w are related through…”

Section: Future Singularitymentioning

confidence: 99%

Stability analysis and future singularity of them²R□^-2Rmodel of non-local gravity

Dirian¹,

Mitsou²

2014

J. Cosmol. Astropart. Phys.

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Abstract. We analyse the classical stability of the model proposed by Maggiore and Mancarella, where gravity is modified by a term ∼ m 2 R −2 R to produce the late-time acceleration of the expansion of the universe. Our study takes into account all excitations of the metric that can potentially drive an instability. There are some subtleties in identifying these modes, as a non-local field theory contains dynamical fields which yet do not correspond to degrees of freedom. Since some of them are ghost-like, we clarify the impact of such modes on the stability of the solutions of interest that are the flat space-time and cosmological solutions. We then find that flat space-time is unstable under scalar perturbations, but the instability manifests itself only at cosmological scales, i.e. out of the region of validity of this solution. It is therefore the stability of the FLRW solution which is relevant there, in which case the scalar perturbations are known to be well-behaved by numerical studies. By finding the analytic solution for the late-time behaviour of the scale factor, which leads to a big rip singularity, we argue that the linear perturbations are bounded in the future because of the domination of Hubble friction. In particular, this effect damps the scalar ghost perturbations which were responsible for destabilizing Minkowski space-time. Thus, the model remains phenomenologically viable.

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Cosmological dynamics and dark energy from nonlocal infrared modifications of gravity

Cited by 72 publications

References 79 publications

BeyondΛCDM: Problems, solutions, and the road ahead

BeyondΛCDM: Problems, solutions, and the road ahead

Infrared Non-local Modifications of General Relativity

Stability analysis and future singularity of them²R□^-2Rmodel of non-local gravity

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Cosmological dynamics and dark energy from nonlocal infrared modifications of gravity

Cited by 72 publications

References 79 publications

BeyondΛCDM: Problems, solutions, and the road ahead

BeyondΛCDM: Problems, solutions, and the road ahead

Infrared Non-local Modifications of General Relativity

Stability analysis and future singularity of them2R□-2Rmodel of non-local gravity

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Product

Resources

About

Stability analysis and future singularity of them²R□^-2Rmodel of non-local gravity