Anisotropic cosmology and inflation from a tilted Bianchi IX model

Sundell, Peter; Koivisto, Tomi S.

doi:10.1103/physrevd.92.123529

Cited by 12 publications

(7 citation statements)

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“…An equally interesting possibility is that anisotropic inflation (see e.g. [153] for a Bianchi IX model of inflation) led to a breaking of statistical isotropy. The best-studied model posits that the power spectrum take the following form [154]…”

Section: Primordial Power Spectrum-broken Isotropymentioning

confidence: 99%

CMB anomalies after Planck

Schwarz

Copi

Huterer

et al. 2016

Class. Quantum Grav.

341

357

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Abstract. Several unexpected features have been observed in the microwave sky at large angular scales, both by WMAP an by Planck. Among those features is a lack of both variance and correlation on the largest angular scales, alignment of the lowest multipole moments with one another and with the motion and geometry of the Solar System, a hemispherical power asymmetry or dipolar power modulation, a preference for odd parity modes and an unexpectedly large cold spot in the Southern hemisphere. The individual p-values of the significance of these features are in the per mille to per cent level, when compared to the expectations of the best-fit inflationary ΛCDM model. Some pairs of those features are demonstrably uncorrelated, increasing their combined statistical significance and indicating a significant detection of CMB features at angular scales larger than a few degrees on top of the standard model. Despite numerous detailed investigations, we still lack a clear understanding of these large-scale features, which seem to imply a violation of statistical isotropy and scale invariance of inflationary perturbations. In this contribution we present a critical analysis of our current understanding and discuss several ideas of how to make further progress.

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Section: Primordial Power Spectrum-broken Isotropymentioning

confidence: 99%

CMB anomalies after Planck

Schwarz

Copi

Huterer

et al. 2016

Class. Quantum Grav.

341

357

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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

460

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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“…In this letter, I show by a concrete example how a generic Bianchi I space-time dynamically aligns itself with a direction of the vector field a An analysis of Bianchi IX type model with possible inflationary solutions is discussed in Ref. 21. b More generally ,this statement is valid for any perfect fluid with an equation of state −1 ≤ w < −1/3, where P = wρ.…”

Section: Introductionmentioning

confidence: 96%

Dynamical analysis of anisotropic inflation

Karčiauskas

2016

Mod. Phys. Lett. A

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The inflaton coupling to a vector field via the f (ϕ) 2 Fµν F µν term is used in several contexts in the literature, such as to generate primordial magnetic fields, to produce statistically anisotropic curvature perturbation, to support anisotropic inflation, and to circumvent the η-problem. In this work, I perform dynamical analysis of this system allowing for the most general Bianchi I initial conditions. I also confirm the stability of attractor fixed points along phase-space directions that had not been investigated before. Mod. Phys. Lett. A Downloaded from www.worldscientific.com by PURDUE UNIVERSITY on 06/27/16. For personal use only. M. KarčiauskasGenerally, vector field contribution to the curvature perturbation introduces quadrupolar angular dependence of the power spectrum. In Ref. 12 (see also it was shown that observational constraints on such modulation put very stringent bounds on vector field models. This bound, however, was applied for a particular model of Ref. 16. As it is shown in later sections, a much larger parameter space might be available for model building.In this work, I perform a classical dynamical analysis of the system with a scalar and a vector field which interacts via a f 2 (ϕ)F µν F µν coupling. A similar analysis has been performed in Ref. 17 and much more generally in Ref. 10. It has been also applied in many other contexts, for example, a system of non-Abelian vector fields, 18 a vector field plus a two-form field 19 or DBI type action. 20 Building on the former two works, especially Ref. 10, I extend their treatment by including more general initial conditions and by addressing several issues which have been overlooked in previous works. I also provide exact analytic expressions to determine the asymptotic behavior of this dynamical system.A vector field introduces anisotropic stress. If it contributes to the expansion of the universe, the expansion will be anisotropic. As the (homogeneous, spacelike) vector field picks out only one preferred direction in space, we can assume that the anisotropy of the expansion will be of the axisymmetric Bianchi type I. Moreover, the preferred axis of such anisotropy will be aligned with the direction of the vector field. These two constraints were imposed in previous works on a single vector field. Even if such a configuration is self-consistent, initial conditions can be much more general. In this work, I relax both the constraints and confirm that the axial symmetry as well as the alignment are achieved dynamically if the vector field does not decay.In cases where the vector field is absent, a number of no-hair theorems have been proven, which state that the future attractor of any spatially homogeneous but anisotropic universe (with possible exception of Bianchi IX a ) is the isotropic Friedmann-Robertson-Walker (FRW) universe if the energy density is dominated by the potential energy of a scalar field. 22,b See Ref. 23 for a recent review and Ref. 24 for the most recent work on no-hair theorems. The presence of a vector field introd...

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Anisotropic cosmology and inflation from a tilted Bianchi IX model

Cited by 12 publications

References 53 publications

CMB anomalies after Planck

CMB anomalies after Planck

BeyondΛCDM: Problems, solutions, and the road ahead

Dynamical analysis of anisotropic inflation

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