Gravitational waves in bigravity cosmology

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

doi:10.1088/1475-7516/2015/05/030

Cited by 56 publications

(95 citation statements)

References 59 publications

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“…Since then, an extensive amount of work has been done to study the viability of the theories through metric perturbation theory and structure formation studies [e.g. 109,110,111,112,113,114,115,116]. Unfortunately, although the simplest bigravity models are able to provide viable self-accelerating background expansions, all such models suffer from ghost and/or gradient instabilities [117,112,114,118].…”

Section: Gravity In Cosmologymentioning

confidence: 99%

BeyondΛCDM: Problems, solutions, and the road ahead

Bull

Akrami

Adamek

et al. 2016

Physics of the Dark Universe

459

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

459

210

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“…The evolution of tensor perturbations in this particular class of models has been first studied in [1] and in more detail in [2]. The problem of how cosmological observations are affected by these tensor instabilities and possible ways out are discussed in [50].…”

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confidence: 99%

“…By fine-tuning the amplitude of the unstable tensor mode to be highly suppressed with respect to the one of the physical sector at the end of inflation, one can achieve that the instability does not show up in the physical metric until today. In [2] this fine-tuning is explicitly quantified. The problem of the viability of the model is therefore translated into the question: is the amplitude of the uncoupled tensor mode after inflation sufficiently suppressed with respect to the one of the graviton coupled to matter?…”

mentioning

confidence: 99%

“…In this paper we address this question in detail, i.e., we embed the model of bigravity studied in [2] in an inflationary scenario and determine the amplitude and the spectrum of primordial tensor perturbations generated at the end of inflation. We find an expression for the ratio between the amplitude of the two tensor modes at the beginning of the radiation era as a function of the reheating temperature of the inflationary model.…”

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confidence: 99%

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Inflationary perturbations in bimetric gravity

Cusin¹,

Durrer²,

Guarato³

et al. 2015

J. Cosmol. Astropart. Phys.

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In this paper we study the generation of primordial perturbations in a cosmological setting of bigravity during inflation. We consider a model of bigravity which can reproduce the ΛCDM background and large scale structure and a simple model of inflation with a single scalar field and a quadratic potential. Reheating is implemented with a toy-model in which the energy density of the inflaton is entirely dissipated into radiation. We present analytic and numerical results for the evolution of primordial perturbations in this cosmological setting. We find that the amplitude of tensor perturbations generated during inflation is sufficiently suppressed to avoid the effects of the tensor instability discovered in Refs. [1,2] which develops during the cosmological evolution in the physical sector. We argue that from a pure analysis of the tensor perturbations this bigravity model is compatible with present observations. However, we derive rather stringent limits on inflation from the vector and scalar sectors.

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“…In particular, the existence of scalar and tensor instabilities [62,63], in particular, branches of the background cosmology will be unconstrained by the measurements discussed in this Letter. Note that we have constrained these bimetric models only using information on the propagation speed of GW, although further constraints can be found from the entire GW waveform.…”

Section: -3mentioning

confidence: 98%

Reining in Alternative Gravity

Schmidt

2017

Physics

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The detection of an electromagnetic counterpart (GRB 170817A) to the gravitational-wave signal (GW170817) from the merger of two neutron stars opens a completely new arena for testing theories of gravity. We show that this measurement allows us to place stringent constraints on general scalar-tensor and vector-tensor theories, while allowing us to place an independent bound on the graviton mass in bimetric theories of gravity. These constraints severely reduce the viable range of cosmological models that have been proposed as alternatives to general relativistic cosmology.

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Gravitational waves in bigravity cosmology

Cited by 56 publications

References 59 publications

BeyondΛCDM: Problems, solutions, and the road ahead

BeyondΛCDM: Problems, solutions, and the road ahead

Inflationary perturbations in bimetric gravity

Reining in Alternative Gravity

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