8,537 research outputs found
The String Tension in Two Dimensional Gauge Theories
We review and elaborate on properties of the string tension in
two-dimensional gauge theories. The first model we consider is massive QED in
the limit. We evaluate the leading string tension both in the
fermionic and bosonized descriptions. We discuss the next to leading
corrections in . The next-to-leading terms in the long distance behavior
of the quark-antiquark potential, are evaluated in a certain region of external
versus dynamical charges. The finite temperature behavior is also determined.
In we review the results for the string tension of quarks in cases with
dynamical quarks in the fundamental, adjoint, symmetric and antisymmetric
representations. The screening nature of is re-derived.Comment: 25 pages, Latex. v2: several changes, mainly in section
QED on a momentum lattice
We investigate the possibility of doing momentum space lattice simulations as
an alternative to the conventional method. The procedure is introduced and
tested for quenched QED2 and quenched QED3. Interesting physical applications
to unquenched QED3 and quenched QED4 are also briefly discussed.Comment: 3 pages, To appear in the proceedings of the LATTICE'93 conference,
ILL-(TH)-93-2
Chiral properties of the fixed point action of the Schwinger model
We study the spectrum properties for a recently constructed fixed point
lattice Dirac operator. We also consider the problem of the extraction of the
fermion condensate, both by direct computation, and through the Banks-Casher
formula by analyzing the density of eigenvalues of a redefined antihermitean
lattice Dirac operator.Comment: 14 pages (LaTeX), 4 figures (EPS
The Gauge Fields and Ghosts in Rindler Space
We consider 2d Maxwell system defined on the Rindler space with metric
ds^2=\exp(2a\xi)\cdot(d\eta^2-d\xi^2) with the goal to study the dynamics of
the ghosts. We find an extra contribution to the vacuum energy in comparison
with Minkowski space time with metric ds^2= dt^2-dx^2. This extra contribution
can be traced to the unphysical degrees of freedom (in Minkowski space). The
technical reason for this effect to occur is the property of Bogolubov's
coefficients which mix the positive and negative frequencies modes. The
corresponding mixture can not be avoided because the projections to positive
-frequency modes with respect to Minkowski time t and positive -frequency modes
with respect to the Rindler observer's proper time \eta are not equivalent. The
exact cancellation of unphysical degrees of freedom which is maintained in
Minkowski space can not hold in the Rindler space. In BRST approach this effect
manifests itself as the presence of BRST charge density in L and R parts. An
inertial observer in Minkowski vacuum |0> observes a universe with no net BRST
charge only as a result of cancellation between the two. However, the Rindler
observers who do not ever have access to the entire space time would see a net
BRST charge. In this respect the effect resembles the Unruh effect. The effect
is infrared (IR) in nature, and sensitive to the horizon and/or boundaries. We
interpret the extra energy as the formation of the "ghost condensate" when the
ghost degrees of freedom can not propagate, but nevertheless do contribute to
the vacuum energy. Exact computations in this simple 2d model support the claim
made in [1] that the ghost contribution might be responsible for the observed
dark energy in 4d FLRW universe.Comment: Final version to appear in Phys. Rev. D. Comments on relation with
energy momentum computations and few new refs are adde
Interpretations of the Accelerating Universe
It is generally argued that the present cosmological observations support the
accelerating models of the universe, as driven by the cosmological constant or
`dark energy'. We argue here that an alternative model of the universe is
possible which explains the current observations of the universe. We
demonstrate this with a reinterpretation of the magnitude-redshift relation for
Type Ia supernovae, since this was the test that gave a spurt to the current
trend in favour of the cosmological constant.Comment: 12 pages including 2 figures, minor revision, references added, a
paragraph on the interpretation of the CMB anisotropy in the QSSC added in
conclusion, general results unchanged. To appear in the October 2002 issue of
the "Publications of the Astronmical Society of the Pacific
The Dyer-Roeder distance in quintessence cosmology and the estimation of H_0 through time-delays
We calculate analytically and numerically the Dyer-Roeder distance in perfect
fluid quintessence models and give an accurate fit to the numerical solutions
for all the values of the density parameter and the quintessence equation of
state. Then we apply our solutions to the estimation of from multiple
image time delays and find that the inclusion of quintessence modifies sensibly
the likelihood distribution of , generally reducing the best estimate
with respect to a pure cosmological constant. Marginalizing over the other
parameters ( and the quintessence equation of state), we obtain
km/sec/Mpc for an empty beam and km/sec/Mpc for
a filled beam. We also discuss the future prospects for distinguishing
quintessence from a cosmological constant with time delays.Comment: 10 pages, 6 figures, submitted to MNRA
Template coexistence in prebiotic vesicle models
The coexistence of distinct templates is a common feature of the diverse
proposals advanced to resolve the information crisis of prebiotic evolution.
However, achieving robust template coexistence turned out to be such a
difficult demand that only a class of models, the so-called package models,
seems to have met it so far. Here we apply Wright's Island formulation of group
selection to study the conditions for the coexistence of two distinct template
types confined in packages (vesicles) of finite capacity. In particular, we
show how selection acting at the level of the vesicles can neutralize the
pressures towards the fixation of any one of the template types (random drift)
and of the type with higher replication rate (deterministic competition). We
give emphasis to the role of the distinct generation times of templates and
vesicles as yet another obstacle to coexistence.Comment: 7 pages, 8 figure
Akns Hierarchy, Self-Similarity, String Equations and the Grassmannian
In this paper the Galilean, scaling and translational self--similarity
conditions for the AKNS hierarchy are analysed geometrically in terms of the
infinite dimensional Grassmannian. The string equations found recently by
non--scaling limit analysis of the one--matrix model are shown to correspond to
the Galilean self--similarity condition for this hierarchy. We describe, in
terms of the initial data for the zero--curvature 1--form of the AKNS
hierarchy, the moduli space of these self--similar solutions in the Sato
Grassmannian. As a byproduct we characterize the points in the Segal--Wilson
Grassmannian corresponding to the Sachs rational solutions of the AKNS equation
and to the Nakamura--Hirota rational solutions of the NLS equation. An explicit
1--parameter family of Galilean self--similar solutions of the AKNS equation
and the associated solution to the NLS equation is determined.Comment: 25 pages in AMS-LaTe
Sum Rules for the Dirac Spectrum of the Schwinger Model
The inverse eigenvalues of the Dirac operator in the Schwinger model satisfy
the same Leutwyler-Smilga sum rules as in the case of QCD with one flavor. In
this paper we give a microscopic derivation of these sum rules in the sector of
arbitrary topological charge. We show that the sum rules can be obtained from
the clustering property of the scalar correlation functions. This argument also
holds for other theories with a mass gap and broken chiral symmetry such as QCD
with one flavor. For QCD with several flavors a modified clustering property is
derived from the low energy chiral Lagrangian. We also obtain sum rules for a
fixed external gauge field and show their relation with the bosonized version
of the Schwinger model. In the sector of topological charge the sum rules
are consistent with a shift of the Dirac spectrum away from zero by
average level spacings. This shift is also required to obtain a nonzero chiral
condensate in the massless limit. Finally, we discuss the Dirac spectrum for a
closely related two-dimensional theory for which the gauge field action is
quadratic in the the gauge fields. This theory of so called random Dirac
fermions has been discussed extensively in the context of the quantum Hall
effect and d-wave super-conductors.Comment: 41 pages, Late
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