Cosmological signatures of anisotropic spatial curvature

Pereira, T.; Marugán, Guillermo A. Mena; Carneiro, S.

doi:10.1088/1475-7516/2015/07/029

Cited by 15 publications

(21 citation statements)

References 61 publications

(100 reference statements)

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“…Most of the attempts to address these anomalies are based on models which respect Gaussianity, but break SI. It is well known, however, that (untilted) anisotropic models of the Universe respect parity [505,506,507], and thus cannot produce correlations between even and odd multipoles, which are hinted at by the quadrupole-octupole alignment.…”

Section: Anomaly Detection: a How-to Guidementioning

confidence: 99%

BeyondΛCDM: Problems, solutions, and the road ahead

Bull

Akrami

Adamek

et al. 2016

Physics of the Dark Universe

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418

204

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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: Anomaly Detection: a How-to Guidementioning

confidence: 99%

BeyondΛCDM: Problems, solutions, and the road ahead

Bull

Akrami

Adamek

et al. 2016

Physics of the Dark Universe

Self Cite

418

204

View full text Add to dashboard Cite

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“…In [42], the impact of a directional spatial curvature on the distribution of type Ia supernovae was also investigated. The linear and gauge-invariant perturbation theory in such models was also shown to be viable in [29], and in several ways parallels that of standard perturbation theory in FLRW spacetimes, though the expected observational signatures are of course different [30]. In this work, motivated by the recent detection of gravitational waves, we focus on the linear dynamics of tensor perturbations in these models.…”

Section: Introductionmentioning

confidence: 94%

“…Here we contribute to this task by investigating a class of homogeneous but spatially anisotropic models such that their time-constant hypersurfaces have a preferred direction, but which nonetheless preserve the observed isotropy of CMB at first order (i.e., without including perturbations). This is possible because the anisotropy of these spacetimes results from the curvature of the spatial sections, and not from the kinematics of expansion [29,30]. From a fundamental perspective, such as in string inspired models of the early universe, one can argue that the early universe's dimensions were initially small and compact [31].…”

Section: Introductionmentioning

confidence: 99%

Tensor perturbations in anisotropically curved cosmologies

Franco

Pereira

2017

J. Cosmol. Astropart. Phys.

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Abstract. Besides expanding anisotropically, the universe can also be anisotropic at the level of its (spatial) curvature. In particular, models with anisotropic curvature and isotropic expansion leads both to a ΛCDM-like phenomenology and to an isotropic and homogeneous CMB at the background level. Thus, they offer an interesting and viable example where the cosmological principle does not follow from the isotropy of observational data. In this paper we extract the linear dynamics of tensor perturbations in two classes of cosmologies with anisotropic spatial curvature. Two difficulties arise in comparison to the same computation in isotropic cosmologies. First, the two tensor polarizations do not behave as a spin-2 field, but rather as the spin-0 and spin-1 irreducible components of a symmetric, traceless and transverse tensor field, each with its own dynamics. Second, because metric perturbations are algebraically coupled, one cannot ignore scalar and vector modes and focus just on tensors -even if one is only interested in the latter -under the penalty of obtaining the wrong equations of motion. We illustrate our results by finding analytical solutions and evaluating the power-spectra of tensor polarizations in a radiation dominated universe. We conclude with some comments on how these models could be constrained with future experiments on CMB polarization.

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“…First, one can check that the choice π µν = 2E µν is a dynamically stable fixed point of the background equations. Moreover, during inflation, the equation governing the perturbations δπ µν of the stress tensor has only decaying modes, so that one can make definite predictions for the perturbed quantities without worrying with the phenomenological model producing such an anisotropic stress [58].…”

Section: B Shear-free Inflationmentioning

confidence: 99%

Isotropization of the universe during inflation

Pereira

Pitrou

2015

Comptes Rendus. Physique

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A primordial inflationary phase allows one to erase any possible anisotropic expansion thanks to the cosmic no-hair theorem. If there is no global anisotropic stress, then the anisotropic expansion rate tends to decrease. What are the observational consequences of a possible early anisotropic phase? We first review the dynamics of anisotropic universes and report analytic approximations. We then discuss the structure of dynamical equations for perturbations and the statistical properties of observables, as well as the implication of a primordial anisotropy on the quantization of these perturbations during inflation. Finally we briefly review models based on primordial vector field which evade the cosmic no-hair theorem.PACS numbers: 98.80.-k, 98.80.Cq

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Cosmological signatures of anisotropic spatial curvature

Cited by 15 publications

References 61 publications

BeyondΛCDM: Problems, solutions, and the road ahead

BeyondΛCDM: Problems, solutions, and the road ahead

Tensor perturbations in anisotropically curved cosmologies

Isotropization of the universe during inflation

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