55 research outputs found
Reality of Complex Affine Toda Solitons
There are infinitely many topological solitons in any given complex affine
Toda theories and most of them have complex energy density. When we require the
energy density of the solitons to be real, we find that the reality condition
is related to a simple ``pairing condition.'' Unfortunately, rather few soliton
solutions in these theories survive the reality constraint, especially if one
also demands positivity. The resulting implications for the physical
applicability of these theories are briefly discussed.Comment: LaTeX, 15 pages, UBTH-049
Low-lying even parity meson resonances and spin-flavor symmetry
A study is presented of the wave meson-meson interactions involving
members of the nonet and of the octet. The starting point is an
SU(6) spin-flavor extension of the SU(3) flavor Weinberg-Tomozawa Lagrangian.
SU(6) symmetry breaking terms are then included to account for the physical
meson masses and decay constants, while preserving partial conservation of the
axial current in the light pseudoscalar sector. Next, the matrix amplitudes
are obtained by solving the Bethe Salpeter equation in coupled-channel with the
kernel built from the above interactions. The poles found on the first and
second Riemann sheets of the amplitudes are identified with their possible
Particle Data Group (PDG) counterparts. It is shown that most of the low-lying
even parity PDG meson resonances, specially in the and sectors,
can be classified according to multiplets of the spin-flavor symmetry group
SU(6). The , and some resonances cannot be
accommodated within this SU(6) scheme and thus they would be clear candidates
to be glueballs or hybrids. Finally, we predict the existence of five exotic
resonances ( and/or ) with masses in the range 1.4--1.6 GeV,
which would complete the , , and multiplets of
SU(3)SU(2).Comment: 43 pages, 2 figures, 61 tables. Improved discussion of Section II. To
appear in Physical Review
Ward-Takahashi Identity with External Field in Ladder QED
We derive the Ward-Takahashi identity obeyed by the fermion-antifermion-gauge
boson vertex in ladder QED in the presence of a constant magnetic field. The
general structure in momentum space of the fermion mass operator with external
electromagnetic field is discussed. Using it we find the solutions of the
ladder WT identity with magnetic field. The consistency of our results with the
solutions of the corresponding Schwinger-Dyson equation ensures the gauge
invariance of the magnetic field induced chiral symmetry breaking recently
found in ladder QED.Comment: new references(refs.10,11) added, 18 pages, Late
``GLUELUMP'' SPECTRUM AND ADJOINT SOURCE POTENTIAL IN LATTICE QCD
We calculate the potential between ``quarks'' which are in the adjoint
representation of SU(2) color in the three-dimensional lattice theory. We work
in the scaling region of the theory and at large quark separations . We also
calculate the masses of color-singlet bound states formed by coupling
an adjoint quark to adjoint glue (``gluelumps''). Good scaling behavior is
found for the masses of both magnetic (angular momentum ) and electric
() gluelumps, and the magnetic gluelump is found to be the lowest-lying
state. It is naively expected that the potential for adjoint quarks should
saturate above a separation where it becomes energetically
favorable to produce a pair of gluelumps. We obtain a good estimate of the
naive screening distance . However we find little evidence of
saturation in the potential out to separations of about twice .Comment: 8 pages plus 8 figures in 2 postscript files (uuencoded
Dynamical Chiral Symmetry Breaking by a Magnetic Field in QED
It is shown that the chiral symmetry is spontaneously broken by a constant
magnetic field in QED. The dynamical mass of fermions (energy gap in the
fermion spectrum) is , where is the
magnetic field, the constant is of order one and is the
renormalized coupling constant. Possible applications of this effect are
discussed.Comment: 12 pages, LaTeX. The final journal version (with minor corrections
Flux-tubes in three-dimensional lattice gauge theories
Flux-tubes in different representations of SU(2) and U(1) lattice gauge
theories in three dimensions are measured. Wilson loops generate heavy
``quark-antiquark'' pairs in fundamental (), adjoint (), and
quartet () representations of SU(2). The first direct lattice
measurements of the flux-tube cross-section as a function of
representation are made. It is found that ,
to about 10\%. Results are consistent with a connection between the string
tension and suggested by a simplified flux-tube model,
[ is the gauge coupling], given
that scales like the Casimir , as observed in previous
lattice studies in both three and four dimensions. The results can discriminate
among phenomenological models of the physics underlying confinement. Flux-tubes
for singly- and doubly-charged Wilson loops in compact QED are also
measured. It is found that the string tension scales as the squared-charge and
the flux-tube cross-section is independent of charge to good approximation.
These SU(2) and U(1) simulations lend some support, albeit indirectly, to a
conjecture that the dual superconductor mechanism underlies confinement in
compact gauge theories in both three and four dimensions.Comment: 15 pages (REVTEX 2.1). Figures: 11, not included (available by
request from [email protected] by regular mail, postscript files, or one
self-unpacking uuencoded file
Direct Instantons in QCD Nucleon Sum Rules
We study the role of direct (i.e. small-scale) instantons in QCD correlation
functions for the nucleon. They generate sizeable, nonperturbative corrections
to the conventional operator product expansion, which improve the quality of
both QCD nucleon sum rules and cure the long-standing stability problem, in
particular, of the chirally odd sum-rule.Comment: 10 pages, UMD PP#93-17
Lagrangian and Hamiltonian Formalism on a Quantum Plane
We examine the problem of defining Lagrangian and Hamiltonian mechanics for a
particle moving on a quantum plane . For Lagrangian mechanics, we
first define a tangent quantum plane spanned by noncommuting
particle coordinates and velocities. Using techniques similar to those of Wess
and Zumino, we construct two different differential calculi on .
These two differential calculi can in principle give rise to two different
particle dynamics, starting from a single Lagrangian. For Hamiltonian
mechanics, we define a phase space spanned by noncommuting
particle coordinates and momenta. The commutation relations for the momenta can
be determined only after knowing their functional dependence on coordinates and
velocities.
Thus these commutation relations, as well as the differential calculus on
, depend on the initial choice of Lagrangian. We obtain the
deformed Hamilton's equations of motion and the deformed Poisson brackets, and
their definitions also depend on our initial choice of Lagrangian. We
illustrate these ideas for two sample Lagrangians. The first system we examine
corresponds to that of a nonrelativistic particle in a scalar potential. The
other Lagrangian we consider is first order in time derivative
On the spectral density from instantons in quenched QCD
We investigate the contribution of instantons to the eigenvalue spectrum of
the Dirac operator in quenched QCD. The instanton configurations that we use
have been derived, elsewhere, from cooled SU(3) lattice gauge fields and, for
comparison, we also analyse a random `gas' of instantons. Using a set of
simplifying approximations, we find a non-zero chiral condensate. However we
also find that the spectral density diverges for small eigenvalues, so that the
chiral condensate, at zero quark mass, diverges in quenched QCD. The degree of
divergence decreases with the instanton density, so that it is negligible for
the smallest number of cooling sweeps but becomes substantial for larger number
of cools. We show that the spectral density scales, that finite volume
corrections are small and we see evidence for the screening of topological
charges. However we also find that the spectral density and chiral condensate
vary rapidly with the number of cooling sweeps -- unlike, for example, the
topological susceptibility. Whether the problem lies with the cooling or with
the identification of the topological charges is an open question. This problem
needs to be resolved before one can determine how important is the divergence
we have found for quenched QCD.Comment: 33 pages, 16 figures (RevTex), substantial revisions; to appear in
Phys.Rev.
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