Conserved charges in (Lovelock) gravity in first order formalism

We derive conserved charges as quasi-local Hamiltonians by covariant phase space methods for a class of geometric Lagrangians that can be written in terms of the spin connection, the vielbein and possibly other tensorial form fields, allowing also for non-zero torsion. We then re-calculate certain known results and derive some new ones in three to six dimensions hopefully enlightening certain aspects of all of them. The quasi-local energy is defined in terms of the metric and not its first derivatives, requiring `regularization' for convergence in most cases. Counter-terms consistent with Dirichlet boundary conditions in first order formalism are shown to be an efficient way to remove divergencies and derive the values of conserved charges, the clear-cut application being metrics with AdS (or dS) asymptotics. The emerging scheme is: all is required to remove the divergencies of a Lovelock gravity is a boundary Lovelock gravity.Comment: 20 pages, no figure

Israel conditions for the Gauss-Bonnet theory and the Friedmann equation on the brane universe

Assuming an Einstein-Gauss-Bonnet theory of gravitation in a ($D \geq 5$)-dimensional spacetime with boundary, we consider the problem of the boundary dynamics given the matter Lagrangian on it. The resulting equation is applied in particular on the derivation of the Friedmann eq. of a 3-brane, understood as the non-orientable boundary of a 5d spacetime. We briefly discuss the contradictory conclusions of the literature.Comment: 8 pages, published versio

Vacuum thin shell solutions in five-dimensional Lovelock gravity

Junction conditions for vacuum solutions in five-dimensional Einstein-Gauss-Bonnet gravity are studied. We focus on those cases where two spherically symmetric regions of space-time are joined in such a way that the induced stress tensor on the junction surface vanishes. So a spherical vacuum shell, containing no matter, arises as a boundary between two regions of the space-time. Such solutions are a generalized kind of spherically symmetric empty space solutions, described by metric functions of the class $C^0$. New global structures arise with surprising features. In particular, we show that vacuum spherically symmetric wormholes do exist in this theory. These can be regarded as gravitational solitons, which connect two asymptotically (Anti) de-Sitter spaces with different masses and/or different effective cosmological constants. We prove the existence of both static and dynamical solutions and discuss their (in)stability under perturbations that preserve the symmetry. This leads us to discuss a new type of instability that arises in five-dimensional Lovelock theory of gravity for certain values of the coupling of the Gauss-Bonnet term.Comment: 9 pages. This is an extended version of the authors' contribution to the Proceedings of the Marcel Grossmann Meeting, held in Paris, 12-18 July 200

Intersecting hypersurfaces, topological densities and Lovelock Gravity

Intersecting hypersurfaces in classical Lovelock gravity are studied exploiting the description of the Lovelock Lagrangian as a sum of dimensionally continued Euler densities. We wish to present an interesting geometrical approach to the problem. The analysis allows us to deal most efficiently with the division of space-time into a honeycomb network of cells produced by an arbitrary arrangement of membranes of matter. We write the gravitational action as bulk terms plus integrals over each lower dimensional intersection. The spin connection is discontinuous at the shared boundaries of the cells, which are spaces of various dimensionalities. That means that at each intersection there are more than one spin connections. We introduce a multi-parameter family of connections which interpolate between the different connections at each intersection. The parameters live naturally on a simplex. We can then write the action including all the intersection terms in a simple way. The Lagrangian of Lovelock gravity is generalized so as to live on the simplices as well. Each intersection term of the action is then obtained as an integral over an appropriate simplex. Lovelock gravity and the associated topological (Euler) density are used as an example of a more general formulation. In this example one finds that singular sources up to a certain co-dimensionality naturally carry matter without introducing conical or other singularities in spacetime geometry.Comment: 24 pages, 2 figures, version 4: lengthened introduction, section on explicit junction conditions for intersections added. Accepted in Journal of Geometry and Physic

Super Heavy Dark Matter Anisotropies from D-particles in the Early Universe

We discuss a way of producing anisotropies in the spectrum of superheavy Dark matter, which are due to the distortion of the inflationary space time induced by the recoil of D-particles upon their scattering with ordinary string matter in the Early Universe. We calculate such distortions by world-sheet Liouville string theory (perturbative) methods. The resulting anisotropies are found to be proportional to the average recoil velocity and density of the D-particles. In our analysis we employ a regulated version of de Sitter space, allowing for graceful exit from inflation. This guarantees the asymptotic flatness of the space time, as required for a consistent interpretation, within an effective field theory context, of the associated Bogolubov coefficients as particle number densities. The latter are computed by standard WKB methods.Comment: 30 pages Latex, two eps figures incorporate

Impact of Low-Energy Constraints on Lorentz Violation

We extend previous analyses of the violation of Lorentz invariance induced in a non-critical string model of quantum space-time foam, discussing the propagation of low-energy particles through a distribution of non-relativistic D-particles.We argue that nuclear and atomic physics experiments do not constitute sensitive probes of this approach to quantum gravity due to a difference in the dispersion relations for massive probes as compared to those for massless ones, predicted by the model.Comment: 4 pages revte

Interaction of heat shock protein (hsp90) with the cytoskeleton: potential implication in intracellular transport

In this article we will summarize the details concerning the association of 90kD heat shock protein (hsp90) with cytoskeletal structures and we will discuss the potential involvement of these interactions in the translocation of steroid hormone receptors to the cell nucleus. In cultured mammalian cells hsp90 has been found to be colocalized with both microtubules and cytokeratin intermediate filaments, whereas no association with actin filaments and vimentin intermediate filaments has been established. The colocalization of hsp90 with microtubules and cytokeratin in intact cells rises the possibility that cytoskeletal structures could serve as "rails" for the direct movement of the steroid hormone receptor via association-dissociation with hsp90 molecules from the cytoplasmic site of synthesis to the nuclear site of action.Biomedical Reviews 1994; 3: 27-37