8,660 research outputs found
On -transforms of one-dimensional diffusions stopped upon hitting zero
For a one-dimensional diffusion on an interval for which 0 is the
regular-reflecting left boundary, three kinds of conditionings to avoid zero
are studied. The limit processes are -transforms of the process stopped
upon hitting zero, where 's are the ground state, the scale function, and
the renormalized zero-resolvent. Several properties of the -transforms are
investigated
Fields in Nonaffine Bundles. I. The general bitensorially covariant differentiation procedure
The standard covariant differentiation procedure for fields in vector bundles
is generalised so as to be applicable to fields in general nonaffine bundles in
which the fibres may have an arbitrary nonlinear structure. In addition to the
usual requirement that the base space should be flat or endowed with its own
linear connection, and that there should be an ordinary gauge connection on the
bundle, it is necessary to require also that there should be an intrinsic,
bundle-group invariant connection on the fibre space. The procedure is based on
the use of an appropriate primary-field (i.e. section) independent connector
that is constructed in terms of the natural fibre-tangent-vector realisation of
the gauge connection. The application to gauged harmonic mappings will be
described in a following article.Comment: 17 page Latex file with some minor misprint corrections and added
color for article originally published in black and whit
N=2 Boundary conditions for non-linear sigma models and Landau-Ginzburg models
We study N=2 nonlinear two dimensional sigma models with boundaries and their
massive generalizations (the Landau-Ginzburg models). These models are defined
over either Kahler or bihermitian target space manifolds. We determine the most
general local N=2 superconformal boundary conditions (D-branes) for these sigma
models. In the Kahler case we reproduce the known results in a systematic
fashion including interesting results concerning the coisotropic A-type branes.
We further analyse the N=2 superconformal boundary conditions for sigma models
defined over a bihermitian manifold with torsion. We interpret the boundary
conditions in terms of different types of submanifolds of the target space. We
point out how the open sigma models correspond to new types of target space
geometry. For the massive Landau-Ginzburg models (both Kahler and bihermitian)
we discuss an important class of supersymmetric boundary conditions which
admits a nice geometrical interpretation.Comment: 48 pages, latex, references and minor comments added, the version to
appear in JHE
New and interesting records of Brazilian bryophytes
This paper presents data on morphology, ecology and distribution of 16 species of bryophytes collected in Pernambuco, Brazil, that are interesting floristic records. Notothylasorbicularis (Schwein.) Sull. is new to Brazil, 11 species are new to the Northeast region of Brazil and 4 species are new to Pernambuco.Dados morfológicos, ecológicos e de distribuição geogråfica são apresentados para 16 espécies de briófitas coletadas no Estado de Pernambuco, Brasil. Notothylas orbicularis (Schwein.) Sull. é registrada pela primeira vez para o Brasil, 11 espécies são novas para a região Nordeste e 4 para o Estado de Pernambuco
Weakly Z symmetric manifolds
We introduce a new kind of Riemannian manifold that includes weakly-, pseudo-
and pseudo projective- Ricci symmetric manifolds. The manifold is defined
through a generalization of the so called Z tensor; it is named "weakly Z
symmetric" and denoted by (WZS)_n. If the Z tensor is singular we give
conditions for the existence of a proper concircular vector. For non singular Z
tensor, we study the closedness property of the associated covectors and give
sufficient conditions for the existence of a proper concircular vector in the
conformally harmonic case, and the general form of the Ricci tensor. For
conformally flat (WZS)_n manifolds, we derive the local form of the metric
tensor.Comment: 13 page
Almost-stationary motions and gauge conditions in General Relativity
An almost-stationary gauge condition is proposed with a view to Numerical
Relativity applications. The time lines are defined as the integral curves of
the timelike solutions of the harmonic almost-Killing equation. This vector
equation is derived by a variational principle, by minimizing the deviations
from isometry. The corresponding almost-stationary gauge condition allows one
to put the field equations in hyperbolic form, both in the free-evolution ADM
and in the Z4 formalisms.Comment: Talk presented at the Spanish Relativity Meeting, September 6-10 2005
Revised versio
T-duality for the sigma model with boundaries
We derive the most general local boundary conditions necessary for T-duality
to be compatible with superconformal invariance of the two-dimensional N=1
supersymmetric nonlinear sigma model with boundaries. To this end, we construct
a consistent gauge invariant parent action by gauging a U(1) isometry, with and
without boundary interactions. We investigate the behaviour of the boundary
conditions under T-duality, and interpret the results in terms of D-branes.Comment: 48 pages, LaTeX, v2: typos corrected, references adde
Collineations of a symmetric 2-covariant tensor: Ricci collineations
The infinitesimal transformations that leave invariant a two-covariant symmetric tensor are studied. The interest of these symmetry transformations lays in the fact that this class of tensors includes the energy-momentum and Ricci tensors. We find that in most cases the class of infinitesimal generators of these transformations is a finite dimensional Lie algebra, but in some cases exhibiting a higher degree of degeneracy, this class is infinite dimensional and may fail to be a Lie algebra. As an application, we study the Ricci collineations of a type B warped spacetime
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