1,549 research outputs found
An N=8 Superaffine Malcev Algebra and Its N=8 Sugawara
A supersymmetric affinization of the algebra of octonions is introduced. It
satisfies a super-Malcev property and is N=8 supersymmetric. Its Sugawara
construction recovers, in a special limit, the non-associative N=8 superalgebra
of Englert et al. This paper extends to supersymmetry the results obtained by
Osipov in the bosonic case.Comment: 10 pages, LaTe
Normal ordering and boundary conditions in open bosonic strings
Boundary conditions play a non trivial role in string theory. For instance
the rich structure of D-branes is generated by choosing appropriate
combinations of Dirichlet and Neumann boundary conditions. Furthermore, when an
antisymmetric background is present at the string end-points (corresponding to
mixed boundary conditions) space time becomes non-commutative there.
We show here how to build up normal ordered products for bosonic string
position operators that satisfy both equations of motion and open string
boundary conditions at quantum level. We also calculate the equal time
commutator of these normal ordered products in the presence of antisymmetric
tensor background.Comment: 7 pages no figures, References adde
G\"odel-type Spacetimes in Induced Matter Gravity Theory
A five-dimensional (5D) generalized G\"odel-type manifolds are examined in
the light of the equivalence problem techniques, as formulated by Cartan. The
necessary and sufficient conditions for local homogeneity of these 5D manifolds
are derived. The local equivalence of these homogeneous Riemannian manifolds is
studied. It is found that they are characterized by three essential parameters
, and : identical triads correspond to
locally equivalent 5D manifolds. An irreducible set of isometrically
nonequivalent 5D locally homogeneous Riemannian generalized G\"odel-type
metrics are exhibited. A classification of these manifolds based on the
essential parameters is presented, and the Killing vector fields as well as the
corresponding Lie algebra of each class are determined. It is shown that the
generalized G\"odel-type 5D manifolds admit maximal group of isometry
with , or depending on the essential parameters ,
and . The breakdown of causality in all these classes of homogeneous
G\"odel-type manifolds are also examined. It is found that in three out of the
six irreducible classes the causality can be violated. The unique generalized
G\"odel-type solution of the induced matter (IM) field equations is found. The
question as to whether the induced matter version of general relativity is an
effective therapy for these type of causal anomalies of general relativity is
also discussed in connection with a recent article by Romero, Tavakol and
Zalaletdinov.Comment: 19 pages, Latex, no figures. To Appear in J.Math.Phys.(1999
Division Algebras and Extended N=2,4,8 SuperKdVs
The first example of an N=8 supersymmetric extension of the KdV equation is
here explicitly constructed. It involves 8 bosonic and 8 fermionic fields. It
corresponds to the unique N=8 solution based on a generalized hamiltonian
dynamics with (generalized) Poisson brackets given by the Non-associative N=8
Superconformal Algebra. The complete list of inequivalent classes of
parametric-dependent N=3 and N=4 superKdVs obtained from the ``Non-associative
N=8 SCA" is also furnished. Furthermore, a fundamental domain characterizing
the class of inequivalent N=4 superKdVs based on the "minimal N=4 SCA" is
given.Comment: 14 pages, LaTe
Central extensions, classical non-equivariant maps and residual symmetries
The arising of central extensions is discussed in two contexts. At first
classical counterparts of quantum anomalies (deserving being named as
"classical anomalies") are associated with a peculiar subclass of the
non-equivariant maps. Further, the notion of "residual symmetry" for theories
formulated in given non-vanishing EM backgrounds is introduced. It is pointed
out that this is a Lie-algebraic, model-independent, concept.Comment: 8 pages, LaTex. Talk given at the International Conference
"Renormalization Group and Anomalies in Gravitation and Cosmology", Ouro
Preto, Brazil, March 2003. To appear in the Proceeding
A class of surfaces with planar lines of curvature
En este articulo estudiamos superficies parametrizadas por lĂneas de curvatura. Obtenemos una caracterizaciĂłn de una clase de superficies con lĂneas de curvatura planas, esta caracterizaciĂłn depende de ciertas funciones holomorfas. Presentamos una clase de superficies con dos familias de lĂneas de curvatura planas, esta clase incluye las superficies de Dupin. TambiĂ©n damos algunos ejemplos explĂcitos.In this paper we study surfaces parameterized by lines of curvature. We obtain a characterization of a class of surfaces with planar lines of curvature, this characterization depend on certain holomorphic function.
We present a class of surfaces with two family of planar lines of curvature, this class of surfaces includes the Dupin surfaces. Also, we give explicit examples
A shared database of underground utility lines for 3D mapping and GIS applications
For the purpose of facility management it is very important to have detailed and up-to-date databases of underground utility lines,
but such data are not always available with adequate accuracy. Hence, the need of collecting and organizing suitable information on
underground services is a fundamental issue when dealing with urban data. Besides, by analyzing the process of designing and laying
new underground infrastructures it is possible to implement an efficient and cost-effective approach to integrate and update existing
maps by exploiting the surveying required for the installation of new facilities. It is also important to underline that collecting all the
data in a unique integrated database (and GIS) gives the possibility to share (at least at a local level) the cartographic and thematic
information for an optimal management of underground networks. In this paper, a database (DB) model for archiving the
underground lines data is presented. The structure of the DB has been designed by following the standard methodology for the
modelling of a relational DB, going through successive phases and originating the external, conceptual and logical model. Finally,
preliminary tests have been carried on for parts of the DB to verify quality parameters
A Self-Organized Method for Computing the Epidemic Threshold in Computer Networks
In many cases, tainted information in a computer network can spread in a way
similar to an epidemics in the human world. On the other had, information
processing paths are often redundant, so a single infection occurrence can be
easily "reabsorbed". Randomly checking the information with a central server is
equivalent to lowering the infection probability but with a certain cost (for
instance processing time), so it is important to quickly evaluate the epidemic
threshold for each node. We present a method for getting such information
without resorting to repeated simulations. As for human epidemics, the local
information about the infection level (risk perception) can be an important
factor, and we show that our method can be applied to this case, too. Finally,
when the process to be monitored is more complex and includes "disruptive
interference", one has to use actual simulations, which however can be carried
out "in parallel" for many possible infection probabilities
On Supergroups with Odd Clifford Parameters and Supersymmetry with Modified Leibniz Rule
We investigate supergroups with Grassmann parameters replaced by odd Clifford
parameters. The connection with non-anticommutative supersymmetry is discussed.
A Berezin-like calculus for odd Clifford variables is introduced. Fermionic
covariant derivatives for supergroups with odd Clifford variables are derived.
Applications to supersymmetric quantum mechanics are made. Deformations of the
original supersymmetric theories are encountered when the fermionic covariant
derivatives do not obey the graded Leibniz property. The simplest non-trivial
example is given by the N=2 SQM with a real multiplet and a cubic
potential. The action is real. Depending on the overall sign ("Euclidean" or
"Lorentzian") of the deformation, a Bender-Boettcher pseudo-hermitian
hamiltonian is encountered when solving the equation of motion of the auxiliary
field. A possible connection of our framework with the Drinfeld twist
deformation of supersymmetry is pointed out.Comment: Final version to be published in Int. J. Mod. Phys. A; 20 page
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