Gauss-Bonnet gravity, brane world models, and non-minimal coupling

We study the case of brane world models with an additional Gauss-Bonnet term in the presence of a bulk scalar field which interacts non-minimally with gravity, via a possible interaction term of the form $-1/2 \xi R \phi^2$. The Einstein equations and the junction conditions on the brane are formulated, in the case of the bulk scalar field. Static solutions of this model are obtained by solving numerically the Einstein equations with the appropriate boundary conditions on the brane. Finally, we present graphically and comment these solutions for several values of the free parameters of the model.Comment: 13 pages,4 figures, published versio

The cosmological constant and dark energy in braneworlds

We review recent attempts to address the cosmological constant problem and the late-time acceleration of the Universe based on braneworld models. In braneworld models, the way in which the vacuum energy gravitates in the 4D spacetime is radically different from conventional 4D physics. It is possible that the vacuum energy on a brane does not curve the 4D spacetime and only affects the geometry of the extra-dimensions, offering a solution to the cosmological constant problem. We review the idea of supersymmetric large extra dimensions that could achieve this and also provide a natural candidate for a quintessence field. We also review the attempts to explain the late-time accelerated expansion of the universe from the large-distance modification of gravity based on the braneworld. We use the Dvali-Gabadadze-Porrati model to demonstrate how one can distinguish this model from dark energy models in 4D general relativity. Theoretical difficulties in this approach are also addressed.Comment: Invited Review for a special Gen. Rel. Grav. issue on Dark Energy, 22 pages, 13 figures, references adde

Domain Wall Dynamics in Brane World and Non-singular Cosmological Models

We study brane cosmology as 4D (4-dimensional) domain wall dynamics in 5D bulk spacetime. For a generic 5D bulk with 3D maximal symmetry, we derive the equation of motion of a domain wall and find that it depends on mass function of the bulk spacetime and the energy-momentum conservation in a domain wall is affected by a lapse function in the bulk. Especially, for a bulk spacetime with non-trivial lapse function, energy of matter field on the domain wall goes out or comes in from the bulk spacetime. Applying our result to the case with SU(2) gauge bulk field, we obtain a singularity-free universe in brane world scenario, that is, not only a big bang initial singularity of the brane is avoided but also a singularity in a 5D bulk does not exist.Comment: 12 pages, 11 figures, submitted to PRD. One reference is added. (v2

Graviton localization and Newton's law for brane models with a non-minimally coupled bulk scalar field

Brane world models with a non-minimally coupled bulk scalar field have been studied recently. In this paper we consider metric fluctuations around an arbitrary gravity-scalar background solution, and we show that the corresponding spectrum includes a localized zero mode which strongly depends on the profile of the background scalar field. For a special class of solutions, with a warp factor of the RS form, we solve the linearized Einstein equations, for a point-like mass source on the brane, by using the brane bending formalism. We see that general relativity on the brane is recovered only if we impose restrictions on the parameter space of the models under consideration.Comment: 17 pages, revised versio

Lorentz Invariance and Origin of Symmetries

In this letter we reconsider the role of Lorentz invariance in the dynamical generation of the observed internal symmetries. We argue that, generally, Lorentz invariance can only be imposed in the sense that all Lorentz non-invariant effects caused by the spontaneous breakdown of Lorentz symmetry are physically unobservable. Remarkably, the application of this principle to the most general relativistically invariant Lagrangian, with arbitrary couplings for all the fields involved, leads by itself to the appearance of a symmetry and, what is more, to the massless vector fields gauging this symmetry in both Abelian and non-Abelian cases. In contrast, purely global symmetries are only generated as accidental consequences of the gauge symmetry.Comment: 10 page LaTeX fil

Creation of a brane world with Gauss-Bonnet term

We study a creation of a brane world using an instanton solution. We analyze a brane model with a Gauss-Bonnet term in a bulk spacetime. The curvature of 3-brane is assumed to be closed, flat, or open. We construct instanton solutions with branes for those models, and calculate the value of the actions to discuss an initial state of a brane universe.Comment: 9 pages, 10 figure

Non-topological gravitating defects in five-dimensional anti-de Sitter space

A class of five-dimensional warped solutions is presented. The geometry is everywhere regular and tends to five-dimensional anti-de Sitter space for large absolute values of the bulk coordinate. The physical features of the solutions change depending on the value of an integer parameter. In particular, a set of solutions describes generalized gravitating kinks where the scalar field interpolates between two different minima of the potential. The other category of solutions describes instead gravitating defects where the scalar profile is always finite and reaches the same constant asymptote both for positive and negative values of the bulk coordinate. In this sense the profiles are non-topological. The physical features of the zero modes are discussed.Comment: 9 pages, 4 figure

Management Of Bilateral Temporomandibular Joint Ankylosis In Children: Case Report

Long standing temporomandibular joint (TMJ) ankylosis may cause severe facial deformity and growth retardation as well as psychological problems when it occurs in children. Different kinds of opinion have been advanced as regards its management. This article discusses the aetiology and management of bilateral TMJ ankylosis in form of a case report in a patient with severe facial deformity, malocclusion and retarded growth following bilateral TMJ ankylosis secondary to trauma. The patient was successfully managed by placement of costochondral grafts and interpositionalarthroplasty with partial temporal myofascial flaps. Good mouth opening was achieved and subsequent follow-ups showed improved mandibular and general body growth as well as psychosocial performance. The aim of this paper is to discuss the management challenges posed by bilateral TMJ ankylosis

Kink-induced symmetry breaking patterns in brane-world SU(3)^3 trinification models

The trinification grand unified theory (GUT) has gauge group SU(3)^3 and a discrete symmetry permuting the SU(3) factors. In common with other GUTs, the attractive nature of the fermionic multiplet assignments is obviated by the complicated multi-parameter Higgs potential apparently needed for phenomenological reasons, and also by vacuum expectation value (VEV) hierarchies within a given multiplet. This motivates the rigorous consideration of Higgs potentials, symmetry breaking patterns and alternative symmetry breaking mechanisms in models with this gauge group. Specifically, we study the recently proposed ``clash of symmetries'' brane-world mechanism to see if it can help with the symmetry breaking conundrum. This requires a detailed analysis of Higgs potential global minima and kink or domain wall solutions interpolating between the disconnected global minima created through spontaneous discrete symmetry breaking. Sufficiently long-lived metastable kinks can also be considered. We develop what we think is an interesting, albeit speculative, brane-world scheme whereby the hierarchical symmetry breaking cascade, trinification to left-right symmetry to the standard model to colour cross electromagnetism, may be induced without an initial hierarchy in vacuum expectation values. Another motivation for this paper is simply to continue the exploration of the rich class of kinks arising in models that are invariant under both discrete and continuous symmetries.Comment: 12 pages, RevTex, references adde

Experience and imagination in transdisciplinary design: The fabpod

© 2018 Informa UK Limited, trading as Taylor & Francis Group. This article examines how techniques for imagining atmospheres are conceptualized and practiced in architecture, anthropology and acoustic measurement in order to advance discussion of how transdisciplinary theory and practice might be realized. Building on research into the experience of atmospheres of already existing architectural spaces, it discusses how architects, anthropologists and users of designed environments imagine atmospheres. This is explored through an examination of the processes of design, making, quantitative measurement and ethnographic study of an acoustically designed prototype meeting space, the FabPod. It is argued that transdisciplinary dialogue and collaboration offers architecture a new mode through which to participate in imagining and designing atmosphere