2,014 research outputs found
A note on the non-commutative Chern-Simons model on manifolds with boundary
We study field theories defined in regions of the spatial non-commutative
(NC) plane with a boundary present delimiting them, concentrating in particular
on the U(1) NC Chern-Simons theory on the upper half plane. We find that
classical consistency and gauge invariance lead necessary to the introduction
of -space of square integrable functions null together with all their
derivatives at the origin. Furthermore the requirement of closure of
under the *-product leads to the introduction of a novel notion of the
*-product itself in regions where a boundary is present, that in turn yields
the complexification of the gauge group and to consider chiral waves in one
sense or other. The canonical quantization of the theory is sketched
identifying the physical states and the physical operators. These last ones
include ordinary NC Wilson lines starting and ending on the boundary that yield
correlation functions depending on points on the one-dimensional boundary. We
finally extend the definition of the *-product to a strip and comment on
possible relevance of these results to finite Quantum Hall systems.Comment: 15 pages, references added, to appear in International Journal of
Modern Physic
Non standard parametrizations and adjoint invariants of classical groups
We obtain local parametrizations of classical non-compact Lie groups where
adjoint invariants under maximal compact subgroups are manifest. Extension to
non compact subgroups is straightforward. As a by-product parametrizations of
the same type are obtained for compact groups. They are of physical interest in
any theory gauge invariant under the adjoint action, typical examples being the
two dimensional gauged Wess-Zumino-Witten-Novikov models where these
coordinatizations become of extreme usefulness to get the background fields
representing the vacuum expectation values of the massless modes of the
associated (super) string theory.Comment: 11 pages, latex file, La Plata preprint Th-99/01. Minor changes in
the introduction, version to appear in Physics Letters
On the inconsistency of the MLE in certain heteroskedastic regression models
This paper studies the possibility of inconsistency of the maximum likelihood estimators for certain heteroskedastic regression models. These include the Poisson regression model and the ARCH models.
Correlation functions in the non-commutative Wess-Zumino-Witten model
We develop a systematic perturbative expansion and compute the one-loop
two-points, three-points and four-points correlation functions in a
non-commutative version of the U(N) Wess-Zumino-Witten model in different
regimes of the -parameter showing in the first case a kind of phase
transition around the value , where is a ultraviolet cut-off in a Schwinger regularization
scheme. As a by-product we obtain the functions of the renormalization group,
showing they are essentially the same as in the commutative case but applied to
the whole U(N) fields; in particular there exists a critical point where they
are null, in agreement with a recent background field computation of the
beta-function, and the anomalous dimension of the Lie algebra-valued field
operator agrees with the current algebra prediction. The non-renormalization of
the level is explicitly verified from the four-points correlator, where a
left-right non-invariant counter-term is needed to render finite the theory,
that it is however null on-shell. These results give support to the equivalence
of this model with the commutative one.Comment: 21 pages, latex, no figures, shortened version to appear in Physics
Letters
Functions of cell surface galectin-glycoprotein lattices
Programmed remodeling of cell surface glycans by the sequential action of specific glycosyltransferases can control biological processes by generating or masking ligands for endogenous lectins. Galectins, a family of animal lectins with affinity for beta-galactosides, can form multivalent complexes with cell surface glycoconjugates and deliver a variety of intracellular signals to modulate cell activation, differentiation, and survival. Recent efforts involving genetic or biochemical manipulation of O-glycosylation and N-glycosylation pathways, as well as blockade of the synthesis of endogenous galectins, have illuminated essential roles for galectin-glycoprotein lattices in the control of biological processes including receptor turnover and endocytosis, host-pathogen interactions, and immune cell activation and homeostasis.Fil: Rabinovich, Gabriel Adrián. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Química Biológica de la Facultad de Ciencias Exactas y Naturales; ArgentinaFil: Toscano, Marta Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas. Instituto de Biología y Medicina Experimental. Fundación de Instituto de Biología y Medicina Experimental. Instituto de Biología y Medicina Experimental; ArgentinaFil: Jackson, Shawn S.. University of Maryland; Estados UnidosFil: Vasta, Gerardo R.. University of Maryland; Estados Unido
Supertubes and special holonomy
We obtain a -supersymmetric 6-brane solution of IIA Supergravity by
T-dualizing the supertube recently found. The resulting electric
charge is related to the original -brane charge. The uplifted solution to
eleven dimensions results to be a purely geometrical configuration, which can
be interpreted as a bound state of a Taub-NUT space and a pp-wave. Being the
non trivial part of the metric pseudo-Riemannian, the resulting reduced
holonomy group is non-compact and locally isomorphic to a semidirect product of
an Abelian four dimensional group and SU(2).Comment: 11 pages, latex, no figure
Non-Markovian non-stationary completely positive open quantum system dynamics
By modeling the interaction of a system with an environment through a renewal
approach, we demonstrate that completely positive non-Markovian dynamics may
develop some unexplored non-standard statistical properties. The renewal
approach is defined by a set of disruptive events, consisting in the action of
a completely positive superoperator over the system density matrix. The random
time intervals between events are described by an arbitrary waiting-time
distribution. We show that, in contrast to the Markovian case, if one performs
a system-preparation (measurement) at an arbitrary time, the subsequent
evolution of the density matrix evolution is modified. The non-stationary
character refers to the absence of an asymptotic master equation even when the
preparation is performed at arbitrary long times. In spite of this property, we
demonstrate that operator expectation values and operators correlations have
the same dynamical structure, establishing the validity of a non-stationary
quantum regression hypothesis. The non-stationary property of the dynamic is
also analyzed through the response of the system to an external weak
perturbation.Comment: 13 pages, 3 figure
El problema de diagenesis y metamorfismo en el grupo de Bokkeveld de Sud África y las Sierras Australes de la provincia de Buenos Aires
En base a la estratigrafía y tectónica del Grupo de Bokkeveld, suministrado por S0EK0R de Sud Africa, se han ubicado las muestras utilizadas en el presente trabajo. Las muestras de las Sierras Australes, fueron tomadas de los Grupos de Ventana y Pillahuincó, de uno de los perfiles realizados por T. Suero (1967).
El estudio Petrográfico de las Rocas de Bokkeveld y S. de la Ventana, muestran una gran similitud y homogeneidad entre ellas. Deben considerarse como rocas Sedimentarias, por la presencia de montmorillonita y de minerales interestratificados de arcillas. Las plagioclasas presentan una composición demasiado básica para incluir las rocas dentro del metamorfismo de bajo rango. Lá presencia de epidoto en las formaciones Bonete y Tunas se considera de origen hidrotermal.The samples used in this study have been selected taking into account the stratigraphy and tectonic of the Bokkeveld Group, submitted by SOEKOR Co. The rocks from the Southern Hills, Buenos Aires, were obtained from Ventana and Pilla- huincd Groups, on the basis of the profile from T. Suero.
The petrographic studies of the rocks of Bokkeveld and Ventana Hills, show that there is homogenity and similitude in them. They should be considered as sedimentary rocks, sincje there is montmorillonite and interstratified clay minerals in them.
The plagioclases are too basic to include this rocks in the very low range of metamorphism. Epidote, in Bonete and Tunas Formations, should be considered of hydrothermal and not of metamorphic origin
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