1,325 research outputs found
Meson Correlation Functions in the epsilon-Regime
We present a numerical pilot study of the meson correlation functions in the
epsilon-regime of chiral perturbation theory. Based on simulations with overlap
fermions we measured the axial and pseudo-scalar correlation functions, and we
discuss the implications for the leading low energy constants in the chiral
Lagrangian.Comment: 3 pages, 3 figures, talk presented at Lattice2003(chiral
Simulating chiral quarks in the epsilon-regime of QCD
We present simulation results for lattice QCD with chiral fermions in small
volumes, where the epsilon-expansion of chiral perturbation theory applies. Our
data for the low lying Dirac eigenvalues, as well as mesonic correlation
functions, are in agreement with analytical predictions. This allows us to
extract values for the leading Low Energy Constants F_{pi} and Sigma.Comment: 4 pages, talk presented by W.B. at Baryons04 (Paris, October 25 - 29,
2004); one Ref. adde
Comparing lattice Dirac operators with Random Matrix Theory
We study the eigenvalue spectrum of different lattice Dirac operators
(staggered, fixed point, overlap) and discuss their dependence on the
topological sectors. Although the model is 2D (the Schwinger model with
massless fermions) our observations indicate possible problems in 4D
applications. In particular misidentification of the smallest eigenvalues due
to non-identification of the topological sector may hinder successful
comparison with Random Matrix Theory (RMT).Comment: LATTICE99(topology and confinement), Latex2e using espcrc2.sty, 3
pages, 3 figure
Second Class Constraints in a Higher-Order Lagrangian Formalism
We consider the description of second-class constraints in a Lagrangian path integral associated with a higher-order -operator. Based on two conjugate higher-order -operators, we also propose a Lagrangian path integral with symmetry, and describe the corresponding system in the presence of second-class constraints
Spacetime locality in Sp(2) symmetric lagrangian formalism
The existence of a local solution to the Sp(2) master equation for gauge
field theory is proven in the framework of perturbation theory and under
standard assumptions on regularity of the action. The arbitrariness of
solutions to the Sp(2) master equation is described, provided that they are
proper. It is also shown that the effective action can be chosen to be Sp(2)
and Lorentz invariant (under the additional assumption that the gauge
transformation generators are Lorentz tensors).Comment: LaTeX, 13 pages, minor misprints correcte
The Several Guises of the BRST Symmetry
We present several forms in which the BRST transformations of QCD in
covariant gauges can be cast. They can be non-local and even not manifestly
covariant. These transformations may be obtained in the path integral formalism
by non standard integrations in the ghost sector or by performing changes of
ghost variables which leave the action and the path integral measure invariant.
For different changes of ghost variables in the BRST and anti-BRST
transformations these two transformations no longer anticommute.Comment: 3 pages, revte
Smooth Bosonization as a Quantum Canonical Transformation
We consider a 1+1 dimensional field theory which contains both a complex
fermion field and a real scalar field. We then construct a unitary operator
that, by a similarity transformation, gives a continuum of equivalent theories
which smoothly interpolate between the massive Thirring model and the
sine-Gordon model. This provides an implementation of smooth bosonization
proposed by Damgaard et al. as well as an example of a quantum canonical
transformation for a quantum field theory.Comment: 20 pages, revte
Unstable Modes in Three-Dimensional SU(2) Gauge Theory
We investigate SU(2) gauge theory in a constant chromomagnetic field in three
dimensions both in the continuum and on the lattice. Using a variational method
to stabilize the unstable modes, we evaluate the vacuum energy density in the
one-loop approximation. We compare our theoretical results with the outcomes of
the numerical simulations.Comment: 24 pages, REVTEX 3.0, 3 Postscript figures included. (the whole
postscript file (text+figures) is available on request from
[email protected]
Axial Correlation Functions in the epsilon-Regime: a Numerical Study with Overlap Fermions
We present simulation results employing overlap fermions for the axial
correlation functions in the epsilon-regime of chiral perturbation theory. In
this regime, finite size effects and topology play a dominant role. Their
description by quenched chiral perturbation theory is compared to our numerical
results in quenched QCD. We show that lattices with a linear extent L > 1.1 fm
are necessary to interpret the numerical data obtained in distinct topological
sectors in terms of the epsilon-expansion. Such lattices are, however, still
substantially smaller than the ones needed in standard chiral perturbation
theory. However, we also observe severe difficulties at very low values of the
quark mass, in particular in the topologically trivial sector.Comment: 15 pages, 6 figures, final version published in JHE
- …