365 research outputs found
Symmetry Breaking in the Schr\"odinger Representation for Chern-Simons Theories
This paper discusses the phenomenon of spontaneous symmetry breaking in the
Schr\"odinger representation formulation of quantum field theory. The analysis
is presented for three-dimensional space-time abelian gauge theories with
either Maxwell, Maxwell-Chern-Simons, or pure Chern-Simons terms as the gauge
field contribution to the action, each of which leads to a different form of
mass generation for the gauge fields.Comment: 16pp, LaTeX , UCONN-94-
Gluon Condensates, Chiral Symmetry Breaking and Pion Wave Function
We consider here chiral symmetry breaking in quantum chromodynamics arising
from gluon condensates in vacuum. Through coherent states of gluons simulating
a mean field type of approximation, we show that the off-shell gluon
condensates of vacuum generate a mass-like contribution for the quarks, giving
rise to chiral symmetry breaking. We next note that spontaneous breaking of
global chiral symmetry links the four component quark field operator to the
pion wave function. This in turn yields many hadronic properties in the light
quark sector in agreement with experiments, leading to the conclusion that low
energy hadron properties are primarily driven by the vacuum structure of
quantum chromodynamics.Comment: 25 pages, IP/BBSR/92-76, revte
Bose-Einstein condensation for interacting scalar fields in curved spacetime
We consider the model of self-interacting complex scalar fields with a rigid
gauge invariance under an arbitrary gauge group . In order to analyze the
phenomenon of Bose-Einstein condensation finite temperature and the possibility
of a finite background charge is included. Different approaches to derive the
relevant high-temperature behaviour of the theory are presented.Comment: 28 pages, LaTe
Technical knowledge and water resources management: A comparative study of river basin councils, Brazil
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/94603/1/wrcr12258.pd
Cosmological Phase Transitions and Radius Stabilization in Higher Dimensions
Recently there has been considerable interest in field theories and string
theories with large extra spacetime dimensions. In this paper, we explore the
role of such extra dimensions for cosmology, focusing on cosmological phase
transitions in field theory and the Hagedorn transition and radius
stabilization in string theory. In each case, we find that significant
distinctions emerge from the usual case in which such large extra dimensions
are absent. For example, for temperatures larger than the scale of the
compactification radii, we show that the critical temperature above which
symmetry restoration occurs is reduced relative to the usual four-dimensional
case, and consequently cosmological phase transitions in extra dimensions are
delayed. Furthermore, we argue that if phase transitions do occur at
temperatures larger than the compactification scale, then they cannot be of
first-order type. Extending our analysis to string theories with large internal
dimensions, we focus on the Hagedorn transition and the new features that arise
due to the presence of large internal dimensions. We also consider the role of
thermal effects in establishing a potential for the radius of the compactified
dimension, and we use this to propose a thermal mechanism for generating and
stabilizing a large radius of compactification.Comment: 37 pages, LaTeX, 5 figure
Worldline path integral for the massive Dirac propagator : A four-dimensional approach
We simplify and generalize an approach proposed by Di Vecchia and Ravndal to
describe a massive Dirac particle in external vector and scalar fields. Two
different path integral representations for the propagator are derived
systematically without the usual five-dimensional extension and shown to be
equivalent due to the supersymmetry of the action. They correspond to a
projection on the mass of the particle either continuously or at the end of the
time evolution. It is shown that the supersymmetry transformations are
generated by shifting and scaling the supertimes and the invariant difference
of two supertimes is given for the general case. A nonrelativistic reduction of
the relativistic propagator leads to a three-dimensional path integral with the
usual Pauli Hamiltonian. By integrating out the photons we obtain the effective
action for quenched QED and use it to derive the gauge-transformation
properties of the general Green function of the theory.Comment: 27 pages, LaTeX, no figures, uses revtex.sty; note with omitted
references added in proo
Stochastic semiclassical cosmological models
We consider the classical stochastic fluctuations of spacetime geometry
induced by quantum fluctuations of massless non-conformal matter fields in the
Early Universe. To this end, we supplement the stress-energy tensor of these
fields with a stochastic part, which is computed along the lines of the
Feynman-Vernon and Schwinger-Keldysh techniques; the Einstein equation is
therefore upgraded to a so called Einstein-Langevin equation. We consider in
some detail the conformal fluctuations of flat spacetime and the fluctuations
of the scale factor in a simple cosmological modelintroduced by Hartle, which
consists of a spatially flat isotropic cosmology driven by radiation and dust.Comment: 29 pages, no figures, ReVTeX fil
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