Nonlocal Infrared Modifications of Gravity. A Review

Maggiore, Michele

doi:10.1007/978-3-319-51700-1_16

Cited by 57 publications

(122 citation statements)

References 82 publications

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“…[59] for attempts to discard the ( σ ) 2 term. Accepting the presence of higher derivatives allows one to describe the Weyl anomaly as ordinary RGE running of f 0,2 , rather than by modifying Einstein gravity by adding a complicated 'quantum anomalous action' [60][61][62] which encodes the anomalous behavior of generic undefined theories of gravity.…”

Section: Scenarios Compatible With Naturalness Of the Higgs Massmentioning

confidence: 99%

Agravity up to infinite energy

2018

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The self-interactions of the conformal mode of the graviton are controlled, in dimensionless gravity theories (agravity), by a coupling f 0 that is not asymptotically free. We show that, nevertheless, agravity can be a complete theory valid up to infinite energy. When f 0 grows to large values, the conformal mode of the graviton decouples from the rest of the theory and does not hit any Landau pole provided that scalars are asymptotically conformally coupled and all other couplings approach fixed points. Then agravity can flow to conformal gravity at infinite energy. We identify scenarios where the Higgs mass does not receive unnaturally large physical corrections. We also show a useful equivalence between agravity and conformal gravity plus two extra conformally coupled scalars, and we give a simpler form for the renormalization group equations of dimensionless couplings as well as of massive parameters in the presence of the most general matter sector.

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Section: Scenarios Compatible With Naturalness Of the Higgs Massmentioning

confidence: 99%

Agravity up to infinite energy

2018

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“…In particular, at the quantum level there are no creation/annihilation operators associated to it. A similar example, worked out in detail in [22], is given by the Polyakov quantum effective action in two dimensions. For two-dimensional gravity coupled to conformal matter it is possible to compute exactly the quantum effective action by integrating the conformal anomaly.…”

Section: Localization and Degrees Of Freedommentioning

confidence: 99%

“…We focus on the RT model, that eventually turns out to be the most interesting phenomenologically. In order to make the paper self-contained, we begin by reviewing material on the background evolution already discussed and reviewed in [20,22,23,84]. We will then move to a detailed discussion of the perturbations and an updated comparison with the cosmological data.…”

Section: Phenomenology Of the Rt Modelmentioning

confidence: 99%

“…As a next step, we discuss the initial conditions on the auxiliary fields (we follow refs. [22,87]).…”

Section: Initial Conditions; the Parameter ∆Nmentioning

confidence: 99%

“…A). For the evolution during an early dS phase the situation is, however, different [22,87]. Indeed, let us denote by x in the value of x = ln a at a time, during inflation, when we set initial conditions u 1 ∼ a 1 ∼ a 2 ∼ O(1), and by x end the value when inflation ends and RD begins (we neglect for simplicity an intermediate reheating phase).…”

Section: Initial Conditions; the Parameter ∆Nmentioning

confidence: 99%

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Gravity in the infrared and effective nonlocal models

Belgacem

Dirian

Finke

et al. 2020

J. Cosmol. Astropart. Phys.

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We provide a systematic and updated discussion of a research line carried out by our group over the last few years, in which gravity is modified at cosmological distances by the introduction of nonlocal terms, assumed to emerge at an effective level from the infrared behavior of the quantum theory. The requirement of producing a viable cosmology turns out to be very stringent and basically selects a unique model, in which the nonlocal term describes an effective mass for the conformal mode. We discuss how such a specific structure could emerge from a fundamental local theory of gravity, and we perform a detailed comparison of this model with the most recent cosmological datasets, confirming that it fits current data at the same level as ΛCDM.Most notably, the model has striking predictions in the sector of tensor perturbations, leading to a very large effect in the propagation of gravitational wave (GWs) over cosmological distances. At the redshifts relevant for the next generation of GW detectors such as Einstein Telescope, Cosmic Explorer and LISA, this leads to deviations from GR that could be as large as 80%, and could be verified with the detection of just a single coalescing binary with electromagnetic counterpart. This would also have potentially important consequences for the search of the counterpart since, for a given luminosity distance to the source, as inferred through the GW signal, the actual source redshift could be significantly different from that predicted by ΛCDM. At the redshifts relevant for advanced LIGO/Virgo/Kagra the effect is smaller, but still potentially observable over a few years of runs at target sensitivity. arXiv:2001.07619v1 [astro-ph.CO] 21 Jan 2020 4 Conclusions 66 A Difficulties of alternative nonlocal models 68 -1 -2 The Lichnerowicz operator is defined by E µν,ρσ ≡ 1 2, where 2 = η µν ∂µ∂ν is the flat-space d'Alembertian. We use the signature ηµν = (−, +, +, +) and MTW [14] sign conventions. 3 We assume here 3 + 1 spacetime dimensions. See [13] for the corresponding equations in d + 1 spacetime dimensions, with d generic.

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Regular Black Holes from Higher-Derivative Effective Delta Sources

Giacchini

Netto

2023

Springer Series in Astrophysics and Cosmology

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Certain approaches to quantum gravity and classical modified gravity theories result in effective field equations in which the original source is substituted by an effective one. In these cases, the occurrence of regular spacetime configurations may be related to the regularity of the effective source, regardless of the specific mechanism behind the regularization. In this chapter, we make an introduction to the effective source formalism applied to higher-derivative gravity. The results presented here, however, can be easily transposed to other frameworks that use similar sources. The generality obtained is also because we consider a general higher-derivative gravity model instead of restricting the analysis to some specific theories. In the first part, we discuss the model in the Newtonian limit, which offers a natural context for introducing effective sources. We show how the regularity properties of the effective sources depend on the behavior of the action's form factor in the ultraviolet regime, which leads to results valid for large families of models (or for families of modified delta sources). Subsequently, we use the general results on the effective sources to construct regular black hole metrics. One of our concerns is the higher-order regularity of the solutions, i.e., the possibility that not only the invariants built with curvature tensors but also the ones with covariant derivatives are regular. In this regard, we present some theorems relating the regularity of sets of curvature-derivative invariants with the regularity properties of the effective sources.

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Nonlocal Infrared Modifications of Gravity. A Review

Cited by 57 publications

References 82 publications

Agravity up to infinite energy

Agravity up to infinite energy

Gravity in the infrared and effective nonlocal models

Regular Black Holes from Higher-Derivative Effective Delta Sources

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