Selfdual 2-form formulation of gravity and classification of energy-momentum tensors

It is shown how the different irreducibility classes of the energy-momentum tensor allow for a Lagrangian formulation of the gravity-matter system using a selfdual 2-form as a basic variable. It is pointed out what kind of difficulties arise when attempting to construct a pure spin-connection formulation of the gravity-matter system. Ambiguities in the formulation especially concerning the need for constraints are clarified.Comment: title changed, extended versio

Yang-Mills theory a la string

A surface of codimension higher than one embedded in an ambient space possesses a connection associated with the rotational freedom of its normal vector fields. We examine the Yang-Mills functional associated with this connection. The theory it defines differs from Yang-Mills theory in that it is a theory of surfaces. We focus, in particular, on the Euler-Lagrange equations describing this surface, introducing a framework which throws light on their relationship to the Yang-Mills equations.Comment: 7 page

The Euler characteristic and the first Chern number in the covariant phase space formulation of string theory

Using a covariant description of the geometry of deformations for extendons, it is shown that the topological corrections for the string action associated with the Euler characteristic and the first Chern number of the normal bundle of the worldsheet, although do not give dynamics to the string, modify the symplectic properties of the covariant phase space of the theory. Future extensions of the present results are outlined.Comment: 12 page

Noether Currents for Bosonic Branes

We consider a relativistic brane propagating in Minkowski spacetime described by any action which is local in its worldvolume geometry. We examine the conservation laws associated with the Poincar\'e symmetry of the background from a worldvolume geometrical point of the view. These laws are exploited to explore the structure of the equations of motion. General expressions are provided for both the linear and angular momentum for any action depending on the worldvolume extrinsic curvature. The conservation laws are examined in perturbation theory. It is shown how non-trivial solutions with vanishing energy-momentum can be constructed in higher order theories. Finally, subtleties associated with boundary terms are examined in the context of the brane Einstein-Hilbert action.Comment: 33 pages, Latex. Published in Annals of Physics 279, 126, 200

Neighbours of Einstein's Equations: Connections and Curvatures

Once the action for Einstein's equations is rewritten as a functional of an SO(3,C) connection and a conformal factor of the metric, it admits a family of ``neighbours'' having the same number of degrees of freedom and a precisely defined metric tensor. This paper analyzes the relation between the Riemann tensor of that metric and the curvature tensor of the SO(3) connection. The relation is in general very complicated. The Einstein case is distinguished by the fact that two natural SO(3) metrics on the GL(3) fibers coincide. In the general case the theory is bimetric on the fibers.Comment: 16 pages, LaTe

Hamilton's equations for a fluid membrane: axial symmetry

Consider a homogenous fluid membrane, or vesicle, described by the Helfrich-Canham energy, quadratic in the mean curvature. When the membrane is axially symmetric, this energy can be viewed as an `action' describing the motion of a particle; the contours of equilibrium geometries are identified with particle trajectories. A novel Hamiltonian formulation of the problem is presented which exhibits the following two features: {\it (i)} the second derivatives appearing in the action through the mean curvature are accommodated in a natural phase space; {\it (ii)} the intrinsic freedom associated with the choice of evolution parameter along the contour is preserved. As a result, the phase space involves momenta conjugate not only to the particle position but also to its velocity, and there are constraints on the phase space variables. This formulation provides the groundwork for a field theoretical generalization to arbitrary configurations, with the particle replaced by a loop in space.Comment: 11 page

Leitura de estudantes surdos: desenvolvimento e peculiaridades em relação à de ouvintes

O Teste de Competência de Leitura de Palavras foi aplicado a 805 estudantes surdos da 1a. série do Ensino Fundamental até a 1a. série do Ensino Médio. Resultados mostraram crescimento significativo da competência de leitura ao longo das séries escolares. O estudo demonstrou que: 1) leitores ouvintes deixam-se enganar mais pela semelhança fonológica, ao passo que leitores surdos deixam-se enganar mais pela semelhança visual; 2) leitores ouvintes deixam-se enganar mais pela homofonia que pela semi-homofonia , ao passo que leitores surdos não; 3) leitores ouvintes deixam-se enganar mais por palavras ortográfica e fonologicamente familiares, ainda que semanticamente inadequadas às figuras, do que por pseudopalavras ortográfica e fonologicamente estranhas, ao passo que leitores surdos privilegiam o processamento semântico-ortográfico do que o ortográfico-fonológico, com melhor detecção de inadequação semântica de palavras conhecidas do que de pseudopalavras.Word Reading Competence Test was applied to 805 deaf students from 1st to 9th grade. Results showed that reading competence increased significantly as a function of school grade. The study demonstrated that: 1) hearing readers were fooled by phonological similarity, whereas deaf readers were fooled by visual similarity; 2) hearing readers were fooled by homophonic items than by semi-homophonic ones, whereas deaf readers were not; 3) hearing readers were more fooled by nonwords that are orthographically and phonologically familiar, even if they were semantically incompatible to the associated pictures, than by non-words that are orthographically and phonologically strange, whereas deaf readers were more focused on semantic-orthographic processing than on orthographic-phonologic one, so as to be superior at detecting the semantic inadequacy of known words

Constraints and Reality Conditions in the Ashtekar Formulation of General Relativity

We show how to treat the constraints and reality conditions in the $SO(3)$-ADM (Ashtekar) formulation of general relativity, for the case of a vacuum spacetime with a cosmological constant. We clarify the difference between the reality conditions on the metric and on the triad. Assuming the triad reality condition, we find a new variable, allowing us to solve the gauge constraint equations and the reality conditions simultaneously.Comment: LaTeX file, 12 pages, no figures; to appear in Classical and Quantum Gravit

Remarks on Conserved Quantities and Entropy of BTZ Black Hole Solutions. Part II: BCEA Theory

The BTZ black hole solution for (2+1)-spacetime is considered as a solution of a triad-affine theory (BCEA) in which topological matter is introduced to replace the cosmological constant in the model. Conserved quantities and entropy are calculated via Noether theorem, reproducing in a geometrical and global framework earlier results found in the literature using local formalisms. Ambiguities in global definitions of conserved quantities are considered in detail. A dual and covariant Legendre transformation is performed to re-formulate BCEA theory as a purely metric (natural) theory (BCG) coupled to topological matter. No ambiguities in the definition of mass and angular momentum arise in BCG theory. Moreover, gravitational and matter contributions to conserved quantities and entropy are isolated. Finally, a comparison of BCEA and BCG theories is carried out by relying on the results obtained in both theories.Comment: PlainTEX, 20 page

Supertubes versus superconducting tubes

In this paper we show the relationship between cylindrical D2-branes and cylindrical superconducting membranes described by a generic effective action at the bosonic level. In the first case the extended objects considered, arose as blown up type IIA superstrings to D2-branes, named supertubes. In the second one, the cosmological objects arose from some sort of field theories. The Dirac-Born-Infeld action describing supertubes is shown to be equivalent to the generic effective action describing superconducting membranes via a special transformation.Comment: Version with minor text changes with respect to the already publishe