The coupling to matter in massive, bi- and multi-gravity

Noller, Johannes; Melville, Scott

doi:10.1088/1475-7516/2015/01/003

Cited by 70 publications

(120 citation statements)

References 67 publications

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“…Refs [121,122,123,124,125,126,127,128,129,130,131,132,133,134,135,136,137] for generalized couplings to matter, Ref. [138] with mass parameters promoted to Lorentz-invariant functions of the Stückelberg fields, and 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

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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

Self Cite

420

210

View full text Add to dashboard Cite

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“…(5)- (9). We can now proceed as earlier: One can use one set of shift equations to solve for one set of boosts.…”

Section: Breaking the Symmetric Vielbein Condition In Multigravitymentioning

confidence: 99%

“…Unlike general relativity, nonminimal couplings to both metrics are not forbidden by any symmetry, and will inevitably arise in any low energy effective field theory of massive gravity or multigravity. A number of possible phenomenological couplings to matter have been explored in the literature [7][8][9][10][11][12][13][14][15][16][17][18][19][20] and their theoretical consistency was explored in [21][22][23][24][25][26][27][28].…”

Section: Introductionmentioning

confidence: 99%

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Vielbein to the rescue? Breaking the symmetric vielbein condition in massive gravity and multigravity

2015

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Nonminimal matter couplings have recently been considered in the context of massive gravity and multigravity. These couplings are free of the Boulware-Deser ghost in the decoupling limit and can thus be considered within an effective field theory setup. Beyond the decoupling limit the ghost was shown to reemerge in the metric formulation of the theory. Recently it was argued that this pathology is absent when formulated in terms of unconstrained vielbeins. We investigate this possibility and show that the BoulwareDeser ghost is always present beyond the decoupling limit in any dimension larger than 2. We also show that the metric and vielbein formulations have an identical ghost-free decoupling limit. Finally we extend these arguments to more generic multigravity theories and argue that for any dimension larger than 2 a ghost is also present in the vielbein formulation whenever the symmetric vielbein condition is spoiled and the equivalence with the metric formulation is lost.

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“…One example would be the coupling of matter to both metrics g µν and f µν simultaneously [27,[45][46][47][48][49], which, however, would introduce the BD ghost if the same matter sector is coupled to both metrics [45,50,51]. Ghost-free (but not always with well-behaved cosmological solutions) scenarios exist if one assumes a coupling through a composite metric [40,50,[52][53][54][55][56][57][58][59]. But even the bimetric gravity with a standard matter coupling could allow for cosmological solutions without any gradient or ghost instabilities at the cost of giving up a FLRW background [60,61].…”

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confidence: 99%

Higuchi ghosts and gradient instabilities in bimetric gravity

Könnig

2015

Phys. Rev. D

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Bimetric gravity theories allow for many different types of cosmological solutions, but not all of them are theoretically allowed. In this work we discuss the conditions to satisfy the Higuchi bound and to avoid gradient instabilities in the scalar sector at the linear level. We find that in expanding universes the ratio of the scale factors of the reference and observable metric has to increase at all times. This automatically implies a ghost-free helicity-2 and helicity-0 sector and enforces a phantom dark energy. Furthermore, the condition for the absence of gradient instabilities in the scalar sector will be analyzed. Finally, we discuss whether cosmological solutions can exist, including exotic evolutions like bouncing cosmologies, in which both the Higuchi ghost and scalar instabilities are absent at all times.

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The coupling to matter in massive, bi- and multi-gravity

Cited by 70 publications

References 67 publications

BeyondΛCDM: Problems, solutions, and the road ahead

BeyondΛCDM: Problems, solutions, and the road ahead

Vielbein to the rescue? Breaking the symmetric vielbein condition in massive gravity and multigravity

Higuchi ghosts and gradient instabilities in bimetric gravity

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