Expansion history and<i>f</i>(<i>R</i>) modified gravity

Fairbairn, Malcolm; Rydbeck, Sara

doi:10.1088/1475-7516/2007/12/005

Cited by 27 publications

(19 citation statements)

References 42 publications

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“…However, this model suffers from a number of problems such as matter instability [215, 244], the instability of cosmological perturbations [146, 74, 544, 526, 251], the absence of the matter era [28, 29, 239], and the inability to satisfy local gravity constraints [469, 470, 245, 233, 154, 448, 134]. The main reason why this model does not work is that the quantity f , RR ≡ ∂ 2 f/ ≡ R 2 is negative.…”

Section: Dark Energy In F(r) Theoriesmentioning

confidence: 99%

f(R) Theories

Felice

Tsujikawa

2010

Living Rev. Relativ.

3,595

3,400

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Over the past decade, f(R) theories have been extensively studied as one of the simplest modifications to General Relativity. In this article we review various applications of f(R) theories to cosmology and gravity — such as inflation, dark energy, local gravity constraints, cosmological perturbations, and spherically symmetric solutions in weak and strong gravitational backgrounds. We present a number of ways to distinguish those theories from General Relativity observationally and experimentally. We also discuss the extension to other modified gravity theories such as Brans-Dicke theory and Gauss-Bonnet gravity, and address models that can satisfy both cosmological and local gravity constraints.

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Section: Dark Energy In F(r) Theoriesmentioning

confidence: 99%

f(R) Theories

Felice

Tsujikawa

2010

Living Rev. Relativ.

3,595

3,400

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“…In particular, the observational viability of some functional forms of f (R) gravity have been studied using mainly SNe Ia, CMB radiation and Large Scale Structure (LSS) data [41,54,42,43].…”

Section: Introductionmentioning

confidence: 99%

Cosmological constraints from the Hubble parameter onf(R) cosmologies

Carvalho

Santos

Alcaniz

et al. 2008

J. Cosmol. Astropart. Phys.

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Abstract. Modified f (R) gravity in the Palatini approach has been presently applied to Cosmology as a realistic alternative to dark energy. In this concern, a number of authors have searched for observational constraints on several f (R) gravity functional forms using mainly data of type Ia supenovae (SNe Ia), Cosmic Microwave Background (CMB) radiation and Large Scale Structure (LSS). In this paper, by considering a homogeneous and isotropic flat universe, we use determinations of the Hubble function H(z), which are based on differential age method, to place bounds on the free parameters of the f (R) = R − β/R n functional form. We also combine the H(z) data with constraints from Baryon Acoustic Oscillations (BAO) and CMB measurements, obtaining ranges of values for n and β in agreement with other independent analyses. We find that, for some intervals of n and β, models based on f (R) = R − β/R n gravity in the Palatini approach, unlike the metric formalism, can produce the sequence of radiation-dominated, matter-dominated, and accelerating periods without need of dark energy.

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“…However, several quantum-gravity theories postulate that familiar concepts such as Lorentz invariance may be broken at energies approaching the Planck energy scale, E P ∼ 1.2×10 19 GeV (e.g., Amelino et al 1998;Jacob & Piran 2008;Liberati & Maccione 2009;Amelino 2013;Tavecchio & Bonnoli 2016). Currently such extreme energies are unreachable by experiments on Earth, but for photons traveling over cosmological distances the accumulated deviations from Lorentz invariance may be measurable using Imaging Atmospheric Cherenkov Telescope facilities, in particular the future Cherenkov Telescope Array (CTA) (e.g., Fairbairn et al 2014;Lorentz & Brun 2017).…”

Section: Introductionmentioning

confidence: 99%

Lorentz Invariance Violation Effects on Gamma–Gamma Absorption and Compton Scattering

Abdalla

Böttcher

2018

ApJ

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In this paper, we consider the impact of Lorentz Invariance Violation (LIV) on the γ − γ opacity of the Universe to VHE-gamma rays, compared to the effect of local under-densities (voids) of the Extragalactic Background Light, and on the Compton scattering process. Both subluminal and superluminal modifications of the photon dispersion relation are considered. In the subluminal case, LIV effects may result in a significant reduction of the γ − γ opacity for photons with energies 10 TeV. However, the effect is not expected to be sufficient to explain the apparent spectral hardening of several observed VHE γ-ray sources in the energy range from 100 GeV -a few TeV, even when including effects of plausible inhomogeneities in the cosmic structure. Superluminal modifications of the photon dispersion relation lead to a further enhancement of the EBL γγ opacity. We consider, for the first time, the influence of LIV on the Compton scattering process. We find that this effect becomes relevant only for photons at ultra-high energies, E 1 PeV. In the case of a superluminal modification of the photon dispersion relation, both the kinematic recoil effect and the Klein-Nishina suppression of the cross section are reduced. However, we argue that the effect is unlikely to be of astrophysical significance.

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Expansion history andf(R) modified gravity

Cited by 27 publications

References 42 publications

f(R) Theories

f(R) Theories

Cosmological constraints from the Hubble parameter onf(R) cosmologies

Lorentz Invariance Violation Effects on Gamma–Gamma Absorption and Compton Scattering

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