Inflationary perturbations in bimetric gravity

Cusin, Giulia; Durrer, Ruth; Guarato, Pietro; Motta, Mariele

doi:10.1088/1475-7516/2015/9/043

Cited by 19 publications

(29 citation statements)

References 63 publications

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“…Our analysis is focussed on the traceless symmetric part of the two tensor sectors: it will not include the scalar and the (typically decaying) vector degrees of freedom. For other works on GW propagation in bigravity, see for example [151][152][153][154][155].…”

Section: Gw Propagation In Bigravitymentioning

confidence: 99%

Testing modified gravity at cosmological distances with LISA standard sirens

Belgacem

Calcagni

Crisostomi

et al. 2019

J. Cosmol. Astropart. Phys.

248

391

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Modifications of General Relativity leave their imprint both on the cosmic ex-Contents A GW luminosity distance and the flux-luminosity relation 53 B Technical details on bigravity 55 B.1 Hassan-Rosen theory of bigravity 55 B.2 Details on the WKB approximation for bigravity 56References 58 5. In the presence of anisotropic stress, or in theories where tensors couple with additional fields already at linearised level (as in theories breaking spatial diffeomorphisms), the tensor evolution equation contains a "source term" Π A in the right hand side of eq. (1.2). In absence of anisotropic stress, and in cosmological scenarios where spatial diffeomorphisms are preserved, we have Π A = 0.The physical consequences of these parameters have been discussed at length in the literature (see [18] for a review on their implications for GW astronomy). In this paper we investigate how they affect a specific observable, the GW luminosity distance, which can be probed by LISA standard sirens. The space-based interferometer LISA can qualitatively and quantitatively improve our tests on the propagation of gravitational waves in theories of modified gravity. LISA can probe signals from standard sirens of supermassive black hole mergers (MBHs) at redshifts z ∼ O(1 − 10), much larger than the redshifts z ∼ O(10 −1 ) of typical sources detectable from second-generation ground-based interferometers. This implies that LISA can test the possible time dependence of the parameters controlling deviations from GR or the standard ΛCDM model, since GWs travel large cosmological distances before reaching the observer. Moreover, as we will review in section 4, LISA can measure the luminosity distance to MBHs with remarkable precision, thereby reaching an accuracy not possible for second-generation ground-based detectors.It is also interesting to observe that LISA can probe GWs in the frequency range in the milli-Hz regime (more precisely, in the interval 10 −4 − 10 0 Hz), much smaller than the typical frequency interval of ground-based detectors, 10 1 − 10 3 Hz. This is a theoretically interesting range to explore since several theories of modified gravity designed to explain dark energy, such as Horndeski, degenerate higher order scalar-tensor (DHOST) theories or massive gravity, have a low UV cutoff, typically of order Λ cutoff ∼ H 2 0 M Pl 1/3 ∼ 10 2 Hz.This cutoff is within the frequency regime probed by LIGO, making a comparison between modified gravity predictions and GW observations delicate [19]. The frequency range tested by LISA, instead, is well below this cutoff, hence it lies within the range of validity of the theories under consideration. The paper is organized as follows. In section 2 we recall the notion of modified GW propagation and GW luminosity distance, that emerges generically in modified theories of gravity. In section 3 we discuss the prediction on modified GW propagation of some of the best studied modified-gravity theories: scalar-tensor theories (with particular emphasis on Horndeski and DHOST theories), infrared non-l...

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Section: Gw Propagation In Bigravitymentioning

confidence: 99%

Testing modified gravity at cosmological distances with LISA standard sirens

Belgacem

Calcagni

Crisostomi

et al. 2019

J. Cosmol. Astropart. Phys.

248

391

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“…This computation was first carried out in [104,105] (see also [106][107][108]). The analysis is complicated by the presence of the square-root matrix g f 1 -whose perturbation around general 18 It should be noted that this first requirement can actually be avoided by demanding only that g c 2 h = mn mn is a solution.…”

Section: Linear Theory On Arbitrary Backgroundmentioning

confidence: 99%

“…At the level of linear perturbations, several degrees of freedom appear without kinetic terms and are thus expected to be strongly coupled [129,203,212]. On top of that, this branch seems to give rise to a nonperturbative ghost [131] and a late-time instability for the tensor modes [107]. Due to these pathologies, most of the literature focusses on branch (II) solutions.…”

Section: Classification Of Solutionsmentioning

confidence: 99%

Recent developments in bimetric theory

Schmidt-May

Strauss

2016

J. Phys. A: Math. Theor.

198

240

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This review is dedicated to recent progress in the field of classical, interacting, massive spin-2 theories, with a focus on ghost-free bimetric theory. We will outline its history and its development as a nontrivial extension and generalisation of nonlinear massive gravity. We present a detailed discussion of the consistency proofs of both theories, before we review Einstein solutions to the bimetric equations of motion in vacuum as well as the resulting mass spectrum. We introduce couplings to matter and then discuss the general relativity and massive gravity limits of bimetric theory, which correspond to decoupling the massive or the massless spin-2 field from the matter sector, respectively. More general classical solutions are reviewed and the present status of bimetric cosmology is summarised. An interesting corner in the bimetric parameter space which could potentially give rise to a nonlinear theory for partially massless spin-2 fields is also discussed. Relations to higher-curvature theories of gravity are explained and finally we give an overview of possible extensions of the theory and review its formulation in terms of vielbeins.

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“…It is quite natural to begin this program from the first part. Indeed, it is highly nontrivial to construct IR modifications of GR that are cosmologically viable, as has been learned from experience with the DGP model [2][3][4][5][6][7][8][9], the dRGT theory of massive gravity [10][11][12][13][14][15][16], Hassan-Rosen bigravity [17][18][19][20][21][22][23][24][25][26][27], or nonlocal models of the Deser-Woodard type [28][29][30][31]. Indeed, none of these attempts has yet produced a viable competitor to ΛCDM.…”

Section: Introductionmentioning

confidence: 99%

Conformal symmetry and nonlinear extensions of nonlocal gravity

Cusin¹,

Foffa²,

Maggiore³

et al. 2016

Phys. Rev. D

Self Cite

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We study two nonlinear extensions of the nonlocal R□ −2 R gravity theory. We extend this theory in two different ways suggested by conformal symmetry, either replacing □ −2 with ð−□ þ R=6Þ −2 , which is the operator that enters the action for a conformally-coupled scalar field, or replacing □ −2 with the inverse of the Paneitz operator, which is a four-derivative operator that enters in the effective action induced by the conformal anomaly. We show that the former modification gives an interesting and viable cosmological model, with a dark energy equation of state today w DE ≃ −1.01, which very closely mimics ΛCDM and evolves asymptotically into a de Sitter solution. The model based on the Paneitz operator seems instead excluded by the comparison with observations. We also review some issues about the causality of nonlocal theories, and we point out that these nonlocal models can be modified so to nicely interpolate between Starobinski inflation in the primordial universe and accelerated expansion in the recent epoch.

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Inflationary perturbations in bimetric gravity

Cited by 19 publications

References 63 publications

Testing modified gravity at cosmological distances with LISA standard sirens

Testing modified gravity at cosmological distances with LISA standard sirens

Recent developments in bimetric theory

Conformal symmetry and nonlinear extensions of nonlocal gravity

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