Fourth order Weyl gravity

Flanagan, Éanna É.

doi:10.1103/physrevd.74.023002

Cited by 91 publications

(88 citation statements)

References 22 publications

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“…The conformally invariant fourth-order Weyl gravity, which includes the scalar field S, the vector field A µ and the tensor field ψ, is given by the action [38]:…”

Section: Conformal Relativitymentioning

confidence: 99%

Conformal Relativity versus Brans–Dicke and Superstring Theories

Blaschke

Dąbrowski

2012

Entropy

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Abstract:We show how conformal relativity is related to Brans-Dicke theory and to low-energy-effective superstring theory. Conformal relativity or the Hoyle-Narlikar theory is invariant with respect to conformal transformations of the metric. We show that the conformal relativity action is equivalent to the transformed Brans-Dicke action for ω = −3/2 (which is the border between standard scalar field and ghost) in contrast to the reduced (graviton-dilaton) low-energy-effective superstring action which corresponds to the Brans-Dicke action with ω = −1. We show that like in ekpyrotic/cyclic models, the transition through the singularity in conformal cosmology in the string frame takes place in the weak coupling regime. We also find interesting self-duality and duality relations for the graviton-dilaton actions.

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“…The conformally invariant fourth-order Weyl gravity, which includes the scalar field S, the vector field A µ and the tensor field ψ, is given by the action [38]:…”

Section: Conformal Relativitymentioning

confidence: 99%

Conformal Relativity versus Brans–Dicke and Superstring Theories

Blaschke

Dąbrowski

2012

Entropy

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“…The latter possibility has been implemented in Ref. [18] where it is explained that it is indeed possible for a theory to have an invariance under conformal transformations without contradicting the fact that conformal invariance is not seen experimentally.…”

Section: Introductionmentioning

confidence: 99%

Spontaneous breaking of conformal invariance, solitons, and gravitational waves in theories of conformally invariant gravitation

Bouchami

Paranjape

2008

Phys. Rev. D

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We study conformal gravity as an alternative theory of gravitation. For conformal gravity to be phenomenologically viable requires that the conformal symmetry is not manifest at the energy scales of the other known physical forces. Hence we are required to find a mechanism for the spontaneous breaking of conformal invariance. In this paper we study the possibility that conformal invariance is spontaneously broken due to interactions with conformally coupled matter fields. The vacuum of the theory admits conformally noninvariant solutions corresponding to maximally symmetric space-times and variants thereof. These are either de Sitter space-time or anti-de Sitter space-time in the full four space-time dimensions and we find new solutions corresponding to maximal symmetry restricted to a lower dimensional subspace. We also consider normalizable, linearized gravitational perturbations around the anti-de Sitter background. We show to second order, that these gravitational fluctuations carry zero energy momentum. Finally we also show the possibility of domain wall solitons interpolating between the ground states of spontaneously broken conformal symmetry that we have found. These solitons necessarily require the vanishing of the scalar field. This offers a way of eschewing the recent suggestion and its consequences [E. Flanagan, Phys. Rev. D 74, 023002 (2006).] that the conformal symmetry could be quarantined to a sterile sector of the theory by choosing an appropriate field redefinition.

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“…ρ+3 p > 0. On the other hand, the modified gravity theories, such as f (R) gravity [31][32][33][34][35], f (T ) gravity [36][37][38][39][40], Weyl gravity [41,42], Gauss-Bonnet gravity [43][44][45][46], Lovelock gravity [47,48], Hořava-Lifshitz gravity [49][50][51], massive gravity [52][53][54][55], heterotic string theory [56] and braneworld scenarios [57][58][59][60], are other approaches for explaining the late time accelerated expansion of the universe. In these modified models, the additional terms in the gravitational Lagrangian play the role of an effective dark energy component with a geometric origin rather than an ad hoc introduction of the dark energy sector with unusual physical features.…”

Section: Introductionmentioning

confidence: 99%

Emergent cosmos in Einstein–Cartan theory

et al. 2018

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Based on Padmanabhan's proposal, the accelerated expansion of the universe can be driven by the difference between the surface and bulk degrees of freedom in a region of space, described by the relation dV /dt = N sur − N bulk where N sur and N bulk = −N em + N de are the degrees of freedom assigned to the surface area and the matter-energy content inside the bulk such that the indices "em" and "de" represent energy-momentum and dark energy, respectively. In the present work, the dynamical effect of the Weyssenhoff perfect fluid with intrinsic spin and its corresponding spin degrees of freedom in the framework of Einstein-Cartan (EC) theory are investigated. Based on the modification of Friedmann equations due to the spin-spin interactions, a correction term for Padmanabhan's original relation dV /dt = N sur +N em −N de including the number of degrees of freedom related with these spin interactions is obtained through the modification in N bulk term as N bulk = −N em + N spin + N de leading to dV /dt = N sur + N em − N spin − N de in which N spin is the corresponding degrees of freedom related with the intrinsic spin of the matter content of the universe. Moreover, the validity of the unified first law and the generalized second law of thermodynamics for the Einstein-Cartan cosmos are investigated. Finally, by considering the covariant entropy conjecture and the bound resulting from the emergent scenario, a total entropy bound is obtained. Using this bound, it is shown that the for the universe as an expanding thermodynamical system, the total effective Komar energy never exceeds the square of the expansion rate with a factor of 3 4π .

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Fourth order Weyl gravity

Cited by 91 publications

References 22 publications

Conformal Relativity versus Brans–Dicke and Superstring Theories

Conformal Relativity versus Brans–Dicke and Superstring Theories

Spontaneous breaking of conformal invariance, solitons, and gravitational waves in theories of conformally invariant gravitation

Emergent cosmos in Einstein–Cartan theory

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