17,722 research outputs found
A Classification of random Dirac fermions
We present a detailed classification of random Dirac hamiltonians in two
spatial dimensions based on the implementation of discrete symmetries. Our
classification is slightly finer than that of random matrices, and contains
thirteen classes. We also extend this classification to non-hermitian
hamiltonians with and without Dirac structure.Comment: 15 pages, version2: typos in the table of classes are correcte
Unitarized pion-nucleon scattering within Heavy Baryon Chiral Perturbation Theory
By means of the Inverse Amplitude Method we unitarize the elastic
pion-nucleon scattering amplitudes obtained from Heavy Baryon Chiral
Perturbation Theory to O(q^3). Within this approach we can enlarge their
applicability range and generate the Delta(1232) resonance. We can find a
reasonable description of the pion nucleon phase shifts with (q^2) parameters
in agreement with the resonance saturation hypothesis. However, the
uncertainties in the analysis of the low energy data as well as the large
number of chiral parameters, which can have strong correlations, allow us to
obtain very good fits with rather different sets of chiral constants.Comment: Shortened version to appear in Phys. Rev. D. Brief Report
How good is the quenched approximation of QCD?
The quenched approximation for QCD is, at present and in the foreseeable
future, unavoidable in lattice calculations with realistic choices of the
lattice spacing, volume and quark masses. In this talk, I review an analytic
study of the effects of quenching based on chiral perturbation theory. Quenched
chiral perturbation theory leads to quantitative insight on the difference
between quenched and unquenched QCD, and reveals clearly some of the diseases
which are expected to plague quenched QCD. Uses jnl.tex and epsf.tex for figure
3. Figures 1 and 2 not included, sorry. Available as hardcopy on request.Comment: 22 pages, Wash. U. HEP/94-62 (Forgotten set of macros now included,
sorry.
Integrable Spin Chain with Reflecting End
A new integrable spin chain of the Haldane-Shastry type is introduced. It is
interpreted as the inverse-square interacting spin chain with a {\it reflecting
end}. The lattice points of this model consist of the square roots of the zeros
of the Laguerre polynomial. Using the ``exchange operator formalism'', the
integrals of motion for the model are explicitly constructed.Comment: 13 pages, REVTeX3, with minor correction
Neutron Electric Dipole Moment with Domain Wall Quarks
We present preliminary results for nucleon dipole moments computed with
domain wall fermions. Our main target is the electric dipole moment of the
neutron arising from the theta term in the gauge part of the QCD lagrangian.
The calculated magnetic dipole moments of the proton and neutron are in rough
accord with experimental values.Comment: 3 pages. Contribution to the proceedings of Lattice 2004 (Fermilab
Scaling functions for O(4) in three dimensions
Monte Carlo simulation using a cluster algorithm is used to compute the
scaling part of the free energy for a three dimensional O(4) spin model. The
results are relevant for analysis of lattice studies of high temperature QCD.Comment: 12 pages, 6 figures, uses epsf.st
Is Heavy Baryon Approach Necessary?
It is demonstrated that using an appropriately chosen renormalization
condition one can respect power counting within the relativistic baryon chiral
perturbation theory without appealing to the technique of the heavy baryon
approach. Explicit calculations are performed for diagrams including two-loops.
It is argued that the introduction of the heavy baryon chiral perturbation
theory was useful but not necessary.Comment: 9 pages, 2 figures, minor changes, references adde
The QCD spectrum with three quark flavors
We present results from a lattice hadron spectrum calculation using three
flavors of dynamical quarks - two light and one strange, and quenched
simulations for comparison. These simulations were done using a one-loop
Symanzik improved gauge action and an improved Kogut-Susskind quark action. The
lattice spacings, and hence also the physical volumes, were tuned to be the
same in all the runs to better expose differences due to flavor number. Lattice
spacings were tuned using the static quark potential, so as a byproduct we
obtain updated results for the effect of sea quarks on the static quark
potential. We find indications that the full QCD meson spectrum is in better
agreement with experiment than the quenched spectrum. For the 0++ (a0) meson we
see a coupling to two pseudoscalar mesons, or a meson decay on the lattice.Comment: 38 pages, 20 figures, uses epsf. 5/29/01 revision responds to
referee's Comments, changes pion fits and tables, and corrects Fig. 10 and
some minor error
Complete one-loop analysis of the nucleon's spin polarizabilities
We present a complete one-loop analysis of the four nucleon spin
polarizabilities in the framework of heavy baryon chiral perturbation theory.
The first non-vanishing contributions to the isovector and first corrections to
the isoscalar spin polarizabilities are calculated. No unknown parameters enter
these predictions. We compare our results to various dispersive analyses. We
also discuss the convergence of the chiral expansion and the role of the delta
isobar.Comment: 4 pp, REVTE
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