114 research outputs found
Symmetries and degrees of freedom in 2-dimensional dual models
The 2-dimensional version of the Schwarz and Sen duality model (Tseytlin
model) is analyzed at the classical and quantum levels. The solutions are
obtained after removing the gauge dependent sector using the Dirac method. The
Poincar\`e invariance is verified at both levels. An extension with global
supersymmetry is also proposed.Comment: 3 pages, revtex, minor correction
Accelerated expansion in bosonic and fermionic 2D cosmologies with quantum effects
In this work we analyze the effects produced by bosonic and fermionic
constituents, including quantum corrections, in two-dimensional (2D)
cosmological models. We focus on a gravitational theory related to the
Callan-Giddings-Harvey-Strominger model, to simulate the dynamics of a young,
spatially-lineal, universe. The cosmic substratum is formed by an {\it
inflaton} field plus a matter component, sources of the 2D gravitational field;
the degrees of freedom also include the presence of a dilaton field. We show
that this combination permits, among other scenarios, the simulation of a
period of inflation, that would be followed by a (bosonic/fermionic) matter
dominated era. We also analyse how quantum effects contribute to the destiny of
the expansion, given the fact that in 2D we have a consistent (renormalizable)
quantum theory of gravity. The dynamical behavior of the system follows from
the solution of the gravitational field equations, the (Klein-Gordon and Dirac)
equations for the sources and the dilaton field equation. Consistent
(accelerated) regimes are present among the solutions of the 2D equations; the
results depend strongly on the initial conditions used for the dilaton field.
In the particular case where fermions are included as matter fields a
transition to a decelerated expansion is possible, something that does not
happen in the exclusively bosonic case.Comment: 6 pages, 5 figures, to appear in EP
Manifest Duality in Born-Infeld Theory
Born-Infeld theory is formulated using an infinite set of gauge fields, along
the lines of McClain, Wu and Yu. In this formulation electromagnetic duality is
generated by a fully local functional. The resulting consistency problems are
analyzed and the formulation is shown to be consistent.Comment: 15 pages, Late
Canonical Quantization of the Maxwell-Chern-Simons Theory in the Coulomb Gauge
The Maxwell-Chern-Simons theory is canonically quantized in the Coulomb gauge
by using the Dirac bracket quantization procedure. The determination of the
Coulomb gauge polarization vector turns out to be intrincate. A set of quantum
Poincar\'e densities obeying the Dirac-Schwinger algebra, and, therefore, free
of anomalies, is constructed. The peculiar analytical structure of the
polarization vector is shown to be at the root for the existence of spin of the
massive gauge quanta.The Coulomb gauge Feynman rules are used to compute the
M\"oller scattering amplitude in the lowest order of perturbation theory. The
result coincides with that obtained by using covariant Feynman rules. This
proof of equivalence is, afterwards, extended to all orders of perturbation
theory. The so called infrared safe photon propagator emerges as an effective
propagator which allows for replacing all the terms in the interaction
Hamiltonian of the Coulomb gauge by the standard field-current minimal
interaction Hamiltonian.Comment: 21 pages, typeset in REVTEX, figures not include
The initial conditions of observed star clusters - I. Method description and validation
We have coupled a fast, parametrized star cluster evolution code to a Markov
Chain Monte Carlo code to determine the distribution of probable initial
conditions of observed star clusters, which may serve as a starting point for
future -body calculations. In this paper we validate our method by applying
it to a set of star clusters which have been studied in detail numerically with
-body simulations and Monte Carlo methods: the Galactic globular clusters
M4, 47 Tucanae, NGC 6397, M22, Centauri, Palomar 14 and Palomar 4, the
Galactic open cluster M67, and the M31 globular cluster G1. For each cluster we
derive a distribution of initial conditions that, after evolution up to the
cluster's current age, evolves to the currently observed conditions. We find
that there is a connection between the morphology of the distribution of
initial conditions and the dynamical age of a cluster and that a degeneracy in
the initial half-mass radius towards small radii is present for clusters which
have undergone a core collapse during their evolution. We find that the results
of our method are in agreement with -body and Monte Carlo studies for the
majority of clusters. We conclude that our method is able to find reliable
posteriors for the determined initial mass and half-mass radius for observed
star clusters, and thus forms an suitable starting point for modeling an
observed cluster\rq{}s evolution.Comment: 39 pages, 28 figures, accepted for publication in MNRA
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