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C. Castro

Publications and source records attributed to C. Castro.

15 recordsLinked to original sources

A new addition theorem for the 3-D Navier-Lam\'e system and its application to the method of fundamental solutions

We obtain a new addition theorem for the fundamental solution of the Navier-Lam\'e system in dimension 3 satisfying the Kupradze radiation conditions. This provides an expansion of this fundamental solution that involves only the evaluation of Bessel functions and scalar spherical harmonics. This is particularly useful in collocation numerical methods based on fundamental solutions, such as the boundary element method or the method of fundamental solutions. For this last method, we show its efficiency when approximating the Navier-Lam\'e system in exterior domains.

math.NA

Live load matrix recovery from scattering data in linear elasticity

We study the numerical approximation of the inverse scattering problem in the two-dimensional homogeneous isotropic linear elasticity with an unknown linear load given by a square matrix. For both backscattering data and fixed-angle scattering data, we show how to obtain numerical approximations of the so-called Born approximations and propose new iterative algorithms that provide sequences of approximations to the unknown load. Numerical evidences of the convergence for not too large loads are also given.

math.AP

A flux-vector splitting scheme for the shallow water equations extended to high-order on unstructured meshes

We present an advection-pressure flux-vector splitting method for the one and two- dimensional shallow water equations following the approach first proposed by Toro and V\'azquez for the compressible Euler equations. The resulting first-order schemes turn out to be exceedingly simple, with accuracy and robustness comparable to that of the sophisticated Godunov upwind method used in conjunction with complete non- linear Riemann solvers. The technique splits the full system into two subsystems, namely an advection system and a pressure system. The sought numerical flux results from fluxes for each of the subsystems. The basic methodology, extended on 2D unstructured meshes, constitutes the building block for the construction of numerical schemes of very high order of accuracy following the ADER approach. The presented numerical schemes are systematically assessed on a carefully selected suite of test problems with reference solutions, in one and two space dimensions.The applicabil- ity of the schemes is illustrated through simulations of tsunami wave propagation in the Pacific Ocean.

math.NA

Clifford Algebra of Spacetime and the Conformal Group

We demonstrate the emergence of the conformal group SO(4,2) from the Clifford algebra of spacetime. The latter algebra is a manifold, called Clifford space, which is assumed to be the arena in which physics takes place. A Clifford space does not contain only points (events), but also lines, surfaces, volumes, etc..., and thus provides a framework for description of extended objects. A subspace of the Clifford space is the space whose metric is invariant with respect to the conformal group SO(4,2) which can be given either passive or active interpretation. As advocated long ago by one of us, active conformal transformations, including dilatations, imply that sizes of physical objects can change as a result of free motion, without the presence of forces. This theory is conceptually and technically very different from Weyl's theory and provides when extended to a curved conformal space a resolution of the long standing problem of realistic masses in Kaluza-Klein theories.

hep-th

Nambu-Goto Strings from SU(N) Born-Infeld model

The spectrum of quenched Yang-Mills theory in the large-N limit displays strings and higher dimensional extended objects. The effective dynamics of string-like excitations is encoded into area preserving Schild action. In this letter, we bridge the gap between SU(N) gauge models and fully reparametrization invariant Nambu-Goto string models by introducing an extra matrix degree of freedom in the Yang-Mills action. In the large-N limit this matrix variable becomes the world-sheet auxiliary field allowing a smooth transition between the Schild and Nambu-Goto strings. The new improved matrix model we propose here can be extended to p-branes provided we enlarge the dimensionality of the target spacetime.

hep-th

Higher Derivative Gravity and Torsion from the Geometry of C-spaces

We start from a new theory (discussed earlier) in which the arena for physics is not spacetime, but its straightforward extension-the so called Clifford space ($C$-space), a manifold of points, lines, areas, etc..; physical quantities are Clifford algebra valued objects, called polyvectors. This provides a natural framework for description of supersymmetry, since spinors are just left or right minimal ideals of Clifford algebra. The geometry of curved $C$-space is investigated. It is shown that the curvature in $C$-space contains higher orders of the curvature in the underlying ordinary space. A $C$-space is parametrized not only by 1-vector coordinates $x^\mu$ but also by the 2-vector coordinates $\sigma^{\mu \nu}$, 3-vector coordinates $\sigma^{\mu \nu \rho}$, etc., called also {\it holographic coordinates}, since they describe the holographic projections of 1-lines, 2-loops, 3-loops, etc., onto the coordinate planes. A remarkable relation between the "area" derivative $\p/ \p \sigma^{\mu \nu}$ and the curvature and torsion is found: if a scalar valued quantity depends on the coordinates $\sigma^{\mu \nu}$ this indicates the presence of torsion, and if a vector valued quantity depends so, this implies non vanishing curvature. We argue that such a deeper understanding of the $C$-space geometry is a prerequisite for a further development of this new theory which in our opinion will lead us towards a natural and elegant formulation of $M$-theory.

hep-th

The QCD Membrane

In this paper we study spatially quenched, SU(N) Yang-Mills theory in the large-N limit. The resulting reduced action shows the same formal look as the Banks-Fischler-Shenker-Susskind M-theory action. The Weyl-Wigner-Moyal symbol of this matrix model is the Moyal deformation of a p(=2)-brane action. Thus, the large-N limit of the spatially quenched SU(N) Yang-Mills is seen to describe a dynamical membrane. By assuming spherical symmetry we compute the mass spectrum of this object in the WKB approximation.

hep-th

On the quantum aspects of the logarithmic corrections to the black hole entropy

A new relativity theory, or more concretely an extended relativity theory, actively developed by one of the authors incorporates 3 basic concepts. They are the old idea of Chew about bootstrapping, Nottale's scale relativity, and enlargement of the conventional time-space by inclusion of noncommutative Clifford manifolds where all p-branes are treated on equal footing. The latter allows one to write a master action functional. The resulting functional equation is simplified and applied to the p-loop oscillator. Its solution represents a generalization of the conventional quantum point oscillator. In addition, it exhibits some novel features: an emergence of two explicit scales delineating the asymptotic regimes (Planck scale region and a smooth region of a quantum point oscillator). In the most interesting Planck scale regime, the solution recovers in an elementary fashion some basic relations of string theory (including string tension quantization and string uncertainty relation). It is shown that the degeneracy of the $first$ collective excited state of the p-loop oscillator yields not only the well-known Bekenstein-Hawking area-entropy linear relation but also the logarithmic corrections therein. In addition we obtain for any number of dimensions the Hawking temperature, the Schwarschild radius, and the inequalities governing the area of a black hole formed in a fusion of two black holes. One of the interesting results is a demonstration that the evaporation of a black hole is limited by the upper bound on its temperature, the Planck temperature.

physics.gen-ph

Quenched, Minisuperspace, Bosonic p-brane Propagator

We borrow the minisuperspace approximation from Quantum Cosmology and the quenching approximation from QCD in order to derive a new form of the bosonic p-brane propagator. In this new approximation we obtain an exact description of both the collective mode deformation of the brane and the center of mass dynamics in the target spacetime. The collective mode dynamics is a generalization of string dynamics in terms of area variables. The final result is that the evolution of a p-brane in the quenched-minisuperspace approximation is formally equivalent to the effective motion of a particle in a spacetime where points as well as hypersurfaces are considered on the same footing as fundamental geometrical objects. This geometric equivalence leads us to define a new tension-shell condition that is a direct extension of the Klein-Gordon condition for material particles to the case of a physical p-brane.

hep-th

p-Branes from Generalized Yang-Mills Theory

We consider the reduced, quenched version of a generalized Yang-Mills action in 4k-dimensional spacetime. This is a new kind of matrix theory which is mapped through the Weyl-Wigner-Moyal correspondence into a field theory over a non-commutative phase space. We show that the ``classical'' limit of this field theory is encoded into the effective action of an open, (4k-1)-dimensional, bulk brane enclosed by a dynamical, Chern-Simons type, (4k-2)-dimensional, boundary brane. The bulk action is a pure volume term, while the boundary action carries all the dynamical degrees of freedom.

hep-th

Chern-Simons Hadronic Bag from Quenched Large-N QCD

SU(N) reduced, quenched, gauge theories have been shown to be related to string theories. We extend this result and show how a 4-dimensional, reduced, quenched, Yang-Mills theory, supplemented by the topological term, can be related through the Wigner-Weyl-Moyal correspondence to an open 3-brane model. The boundary of the 3-brane is described by a Chern-Simons 2-brane. We identify the bulk of the 3-brane with the interior of a hadronic bag and the world-volume of the Chern-Simons 2-brane with the dynamical boundary of the bag. We estimate the value of the induced bag constant to be a little less than 200MeV.

hep-th

P-Loop Oscillator on Clifford Manifolds and Black Hole Entropy

A new relativity theory, or more concretely an extended relativity theory, actively developed by one of the authors incorporated 3 basic concepts. They are the old idea of Chew about bootstrapping, Nottale's scale relativity, and enlargement of the conventional time-space by inclusion of noncommutative Clifford manifolds where all p-branes are treated on equal footing. The latter allowed one to write a master action functional. The resulting functional equation is simplified and applied to the p-loop oscillator. Its respective solution is a generalization of the conventional point oscillator. In addition , it exhibits some novel features: an emergence of two explicit scales delineating the asymptotic regimes (Planck scale region and a smooth region of a conventional point oscillator). In the most interesting Planck scale regime, the solution reproduces in an elementary fashion the basic relations of string theory (including string tension quantization). In addition, it is shown that comparing the massive (super) string degeneracy with the p-loop degeneracy one is arriving at the proportionality between the Shannon entropy of a p-loop oscillator in D-dimensional space and the Bekenstein-Hawking entropy of the black hole of a size comparable with a string scale.

physics.gen-ph

On the WKB quantum equivalence between diverse p-brane actions

We consider an action for a closed, bosonic, p-brane, where the brane tension is not an assigned parameter but rather it is induced by a maximal rank gauge p-form. This model is classically equivalent to the Nambu--Goto/Howe-Tucker model. We investigate how this classical equivalence can be implemented in the path integral framework. For this purpose we adopt a ``first order'' integration procedure over gauge p-forms and a ``shortened'' Fadeev-Popov procedure.

hep-th

String Representation of Quantum Loops

We recover a general representation for the quantum state of a relativistic closed line (loop) in terms of string degrees of freedom.The general form of the loop functional splits into the product of the Eguchi functional, encoding the holographic quantum dynamics, times the Polyakov path integral, taking into account the full Bulk dynamics, times a loop effective action, which is needed to renormalize boundary ultraviolet divergences. The Polyakov string action is derived as an effective actionfrom a phase space,covariant,Schild action, by functionally integrating out the world-sheet coordinates.The area coordinates description of the boundary quantum dynamics, is shown to be induced by the ``zero mode'' of the bulk quantum fluctuations. Finally, we briefly comment about a ``unified, fully covariant'' description of points, loops and strings in terms of Matrix Coordinates.

hep-th

q deformation by intertwining with application to the singular oscillator

We present a version of q-deformed calculus based on deformed counterparts of Darboux intertwining operators. The case in which the deformed transformation function is of the vacuum type is detailed, but the extension to counterparts of excited states used as Darboux transformation functions is also formally discussed. The method leads to second-order Fokker-Planck-like deformed operators which may be considered as supersymmetric partners, though for a sort of q-deformed open systems, i.e., those possessing q nonlocal drift terms, potential part, as well as q-spreaded vacuum fluctuations. The undeformed limit corresponds to the conservative case, since all q nonlocalities wash out. The procedure is applied to the x^{-2} singular oscillator, for which we also present a formal q generalization of the Bagrov-Samsonov coherent states

quant-ph