Bulk singularities and the effective cosmological constant for higher co-dimension branes

Tolley, Andrew J.; Burgess, C. P.; Hoover, D.; Aghababaie, Y.

doi:10.1088/1126-6708/2006/03/091

Cited by 67 publications

(120 citation statements)

References 50 publications

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“…On the other hand, a handful of explicit solutions of this type do exist, including 4D de Sitter solutions [1] for six-dimensional Maxwell-Einstein systems, 2) with positive 6D cosmological constant, Λ. Similar solutions [2] also exist for six-dimensional gauged, chiral supergravity [11], whose relevant bosonic action is…”

Section: No-go Results and The 6d Loopholementioning

confidence: 99%

“…For those who believe that extra dimensions exist this has motivated searching for explicit solutions to the higher-dimensional field equations for which the large four dimensions we see are de Sitter or de Sitter-like. Although a few such solutions are known [1,2], more and more general no-go results [3,4,5,6] show that such solutions are difficult to find 1 Why should this be so?…”

Section: Introductionmentioning

confidence: 99%

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On brane back-reaction and de Sitter solutions in higher-dimensional supergravity

Burgess

Maharana

Nierop

et al. 2012

J. High Energ. Phys.

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We argue that the problem of finding lower-dimensional de Sitter solutions to the classical field equations of higher-dimensional supergravity necessarily requires understanding the back-reaction of whatever localized objects source the bulk fields. However, we also find that most of the details of the back-reacted solutions are not important for determining the lower-dimensional curvature. We find, in particular, a classically exact expression that, for a broad class of geometries, directly relates the curvature of the lower-dimensional geometry to asymptotic properties of various bulk fields near the sources. Specializing to codimension-two sources, we find that the contribution involving the asymptotic behaviour of the warp factor (which has a definite sign for most supergravities and so is usually used to infer a preference for anti-de Sitter geometries) is precisely canceled by the contribution of the sources themselves (that are left out in earlier treatments). We identify which combination of bulk fields survives this cancelation, and so controls the sign of the lower-dimensional geometry, for several supergravities in 6, 10 and 11 dimensions. Our results show precisely why explicit 4D de Sitter solutions to 6D supergravity evade general no-go theorems. As an application we show that all classical compactifications of Type IIB supergravity (and F-theory) to 8 dimensions are 8D-flat if they involve only the metric and the axio-dilaton sourced by codimension-two sources, extending earlier results to include warped solutions and more general source properties.

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Section: No-go Results and The 6d Loopholementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

On brane back-reaction and de Sitter solutions in higher-dimensional supergravity

Burgess

Maharana

Nierop

et al. 2012

J. High Energ. Phys.

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“…[83,85,86,87] and [88] for a review). These models provide especially vivid illustrations since they have fully explicit descriptions in both six and four dimensions.…”

Section: Discussionmentioning

confidence: 99%

Oxidised cosmic acceleration

Wesley

2009

J. Cosmol. Astropart. Phys.

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Abstract:We give detailed proofs of several new no-go theorems for constructing flat fourdimensional accelerating universes from warped dimensional reduction. These new theorems improve upon previous ones by weakening the energy conditions, by including time-dependent compactifications, and by treating accelerated expansion that is not precisely de Sitter. We show that de Sitter expansion violates the higher-dimensional null energy condition (NEC) if the compactification manifold M is one-dimensional, if its intrinsic Ricci scalarR vanishes everywhere, or ifR and the warp function satisfy a simple limit condition. If expansion is not de Sitter, we establish threshold equation-of-state parameters w below which accelerated expansion must be transient. Below the threshold w there are bounds on the number of e-foldings of expansion. If M is one-dimensional orR everywhere vanishing, exceeding the bound implies the NEC is violated. IfR does not vanish everywhere on M, exceeding the bound implies the strong energy condition (SEC) is violated. Observationally, the w thresholds indicate that experiments with finite resolution in w can cleanly discriminate between different models which satisfy or violate the relevant energy conditions.

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“…We should now re-ask the CC question in this context: What choices give near-flat geometries? Sufficient conditions for that are to assume supersymmetry in the extra dimensions, and the absence of coupling of the brane to a specific bulk field [80]; the latter is currently the biggest worry. Supersymmetry in the bulk helps because it forbids a higher-dimensional cosmological constant.…”

Section: Cosmology and The Cosmological Constant Problemmentioning

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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Bulk singularities and the effective cosmological constant for higher co-dimension branes

Cited by 67 publications

References 50 publications

On brane back-reaction and de Sitter solutions in higher-dimensional supergravity

On brane back-reaction and de Sitter solutions in higher-dimensional supergravity

Oxidised cosmic acceleration

BeyondΛCDM: Problems, solutions, and the road ahead

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