63,877 research outputs found
Transport of persistent organic pollutants across the human placenta
Environment International 65, 107-115 (2014
Effect of higher orbital angular momenta in the baryon spectrum
We have performed a Faddeev calculation of the baryon spectrum for the chiral
constituent quark model including higher orbital angular momentum states. We
have found that the effect of these states is important, although a description
of the baryon spectrum of the same quality as the one given by including only
the lowest-order configurations can be obtained. We have studied the effect of
the pseudoscalar quark-quark interaction on the relative position of the
positive- and negative-parity excitations of the nucleon as well as the effect
of varying the strength of the color-magnetic interaction.Comment: 7 pages, 4 figures. To be published in Phys. Rev. C (November 2001
Geometric and Extensor Algebras and the Differential Geometry of Arbitrary Manifolds
We give in this paper which is the third in a series of four a theory of
covariant derivatives of representatives of multivector and extensor fields on
an arbitrary open set U of M, based on the geometric and extensor calculus on
an arbitrary smooth manifold M. This is done by introducing the notion of a
connection extensor field gamma defining a parallelism structure on U, which
represents in a well defined way the action on U of the restriction there of
some given connection del defined on M. Also we give a novel and intrinsic
presentation (i.e., one that does not depend on a chosen orthonormal moving
frame) of the torsion and curvature fields of Cartan's theory. Two kinds of
Cartan's connection operator fields are identified, and both appear in the
intrinsic Cartan's structure equations satisfied by the Cartan's torsion and
curvature extensor fields. We introduce moreover a metrical extensor g in U
corresponding to the restriction there of given metric tensor \slg defined on M
and also introduce the concept a geometric structure (U,gamma,g) for U and
study metric compatibility of covariant derivatives induced by the connection
extensor gamma. This permits the presentation of the concept of gauge
(deformed) derivatives which satisfy noticeable properties useful in
differential geometry and geometrical theories of the gravitational field.
Several derivatives operators in metric and geometrical structures, like
ordinary and covariant Hodge coderivatives and some duality identities are
exhibit.Comment: This paper is an improved version of material contained in
math.DG/0501560, math.DG/0501561, math.DG/050200
A proposal of a Renormalization Group transformation
We propose a family of renormalization group transformations characterized by
free parameters that may be tuned in order to reduce the truncation effects. As
a check we test them in the three dimensional XY model. The Schwinger--Dyson
equations are used to study the renormalization group flow.Comment: Contribution to Lattice'94. uuencoded postscript fil
Geometric Algebras and Extensors
This is the first paper in a series (of four) designed to show how to use
geometric algebras of multivectors and extensors to a novel presentation of
some topics of differential geometry which are important for a deeper
understanding of geometrical theories of the gravitational field. In this first
paper we introduce the key algebraic tools for the development of our program,
namely the euclidean geometrical algebra of multivectors Cl(V,G_{E}) and the
theory of its deformations leading to metric geometric algebras Cl(V,G) and
some special types of extensors. Those tools permit obtaining, the remarkable
golden formula relating calculations in Cl(V,G) with easier ones in Cl(V,G_{E})
(e.g., a noticeable relation between the Hodge star operators associated to G
and G_{E}). Several useful examples are worked in details fo the purpose of
transmitting the "tricks of the trade".Comment: This paper (to appear in Int. J. Geom. Meth. Mod. Phys. 4 (6) 2007)
is an improved version of material appearing in math.DG/0501556,
math.DG/0501557, math.DG/050155
The U(1) phase transition on toroidal and spherical lattices
We have studied the properties of the phase transition in the U(1) compact
pure gauge model paying special atention to the influence of the topology of
the boundary conditions. From the behavior of the energy cumulants and the
observation of an effective \nu -> 1/d on toroidal and spherical lattices, we
conclude that the transition is first order.Comment: LATTICE98(gauge
From thermal to excited-state quantum phase transitions ---the Dicke model
We study the thermodynamics of the full version of the Dicke model, including
all the possible values of the total angular momentum , with both
microcanonical and canonical ensembles. We focus on how the excited-state
quantum phase transition, which only appears in the microcanonical description
of the maximum angular momentum sector, , change to a standard thermal
phase transition when all the sectors are taken into account. We show that both
the thermal and the excited-state quantum phase transitions have the same
origin; in other words, that both are two faces of the same phenomenon. Despite
all the logarithmic singularities which characterize the excited-state quantum
phase transition are ruled out when all the -sectors are considered, the
critical energy (or temperature) still divides the spectrum in two regions: one
in which the parity symmetry can be broken, and another in which this symmetry
is always well defined.Comment: Submitted to PRE. Comments are welcome. V2: Updated to match
published versio
Study of the Coulomb-Higgs transition in the Abelian Higgs Model
The order of the Coulomb-Higgs transition in the U(1)-Higgs model with
unfrozen modulus of the scalar field is studied. Large lattices (up to
in one case) and high statistics are used. We fix and explore
specially a region of -values where metastability is observed. We
study the thermodynamical limit of several observables, in particular, the
latent heat, the specific heat, the decrement of the free energy between the
maxima and the central minimum of the two-peaked histogram, the Binder cumulant
and the displacement of the critical coupling with the lattice size. The
results point towards a second order transition for ,
while for smaller values of the strong metastability growing with the
lattice size seems to derive from a first order character.Comment: 10 pages, Latex, epsfig, uuencoded gzipped tar file, 4 figures
include
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