11,465 research outputs found
Light-Cone Quantization of Gauge Fields
Light-cone quantization of gauge field theory is considered. With a careful
treatment of the relevant degrees of freedom and where they must be
initialized, the results obtained in equal-time quantization are recovered, in
particular the Mandelstam-Leibbrandt form of the gauge field propagator. Some
aspects of the ``discretized'' light-cone quantization of gauge fields are
discussed.Comment: SMUHEP/93-20, 17 pages (one figure available separately from the
authors). Plain TeX, all macros include
Light-Front QCD(1+1) Coupled to Chiral Adjoint Fermions
We consider SU(N) gauge theory in 1+1 dimensions coupled to chiral fermions
in the adjoint representation of the gauge group. With all fields in the
adjoint representation the gauge group is actually SU(N)/Z_N, which possesses
nontrivial topology. In particular, there are N distinct topological sectors
and the physical vacuum state has a structure analogous to a \theta vacuum. We
show how this feature is realized in light-front quantization for the case N=2,
using discretization as an infrared regulator. In the discretized form of the
theory the nontrivial vacuum structure is associated with the zero momentum
mode of the gauge field A^+. We find exact expressions for the degenerate
vacuum states and the analog of the \theta vacuum. The model also possess a
condensate which we calculate. We discuss the difference between this chiral
light-front theory and the theories that have previously been considered in the
equal-time approach.Comment: 14 pages, RevTeX, two figures requiring BoxedEPS.tex. References
added and some typos correcte
Light-Cone Quantization of Electrodynamics
Light-cone quantization of (3+1)-dimensional electrodynamics is discussed,
using discretization as an infrared regulator and paying careful attention to
the interplay between gauge choice and boundary conditions. In the zero
longitudinal momentum sector of the theory a general gauge fixing is performed
and the corresponding relations that determine the constrained modes of the
gauge field are obtained. The constraints are solved perturbatively and the
structure of the theory is studied to lowest nontrivial order. (Talk presented
at ``Theory of Hadrons and Light-Front QCD,'' Polana Zgorzelisko, Poland,
August 1994.)Comment: 6 pages, LaTeX, OSU-NT-94-0
The BES f_0(1810): a new glueball candidate
We analyze the f_0(1810) state recently observed by the BES collaboration via
radiative J/\psi decay to a resonant \phi\omega spectrum and confront it with
DM2 data and glueball theory. The DM2 group only measured \omega\omega decays
and reported a pseudoscalar but no scalar resonance in this mass region. A
rescattering mechanism from the open flavored KKbar decay channel is considered
to explain why the resonance is only seen in the flavor asymmetric \omega\phi
branch along with a discussion of positive C parity charmonia decays to
strengthen the case for preferred open flavor glueball decays. We also
calculate the total glueball decay width to be roughly 100 MeV, in agreement
with the narrow, newly found f_0, and smaller than the expected estimate of
200-400 MeV. We conclude that this discovered scalar hadron is a solid glueball
candidate and deserves further experimental investigation, especially in the
K-Kbar channel. Finally we comment on other, but less likely, possible
assignments for this state.Comment: 11 pages, 4 figures. Major substantive additions, including an
ab-initio, QCD-based computation of the glueball inclusive decay width,
evaluation of final state effects, and enhanced discussion of several
alternative possibilities. Our conclusions are unchanged: the BES f_0(1810)
is a promising glueball candidat
Physical Coupling Schemes and QCD Exclusive Processes
I discuss application of the BLM method to obtain commensurate scale
relations connecting QCD exclusive amplitudes to other observables, in
particular the heavy quark potential.Comment: 7 pages, Latex, uses l-school.sty. Talk given at "New Nonperturbative
Methods and Quantization on the Light Cone," Les Houches, France, 24 Feb.-7
March 1997. To appear in the proceeding
TSIL: a program for the calculation of two-loop self-energy integrals
TSIL is a library of utilities for the numerical calculation of dimensionally
regularized two-loop self-energy integrals. A convenient basis for these
functions is given by the integrals obtained at the end of O.V. Tarasov's
recurrence relation algorithm. The program computes the values of all of these
basis functions, for arbitrary input masses and external momentum. When
analytical expressions in terms of polylogarithms are available, they are used.
Otherwise, the evaluation proceeds by a Runge-Kutta integration of the coupled
first-order differential equations for the basis integrals, using the external
momentum invariant as the independent variable. The starting point of the
integration is provided by known analytic expressions at (or near) zero
external momentum. The code is written in C, and may be linked from C, C++, or
Fortran. A Fortran interface is provided. We describe the structure and usage
of the program, and provide a simple example application. We also compute two
new cases analytically, and compare all of our notations and conventions for
the two-loop self-energy integrals to those used by several other groups.Comment: 31 pages. Updated to reflect new functionality through v1.4 May 2016
and new information about use with C++. Source code and documentation are
available at http://www.niu.edu/spmartin/TSIL or
http://faculty.otterbein.edu/DRobertson/tsil
Optimal Renormalization Scale and Scheme for Exclusive Processes
We use the BLM method to fix the renormalization scale of the QCD coupling in
exclusive hadronic amplitudes such as the pion form factor and the
photon-to-pion transition form factor at large momentum transfer.
Renormalization-scheme-independent commensurate scale relations are established
which connect the hard scattering subprocess amplitudes that control exclusive
processes to other QCD observables such as the heavy quark potential and the
electron-positron annihilation cross section. The commensurate scale relation
connecting the heavy quark potential, as determined from lattice gauge theory,
to the photon-to-pion transition form factor is in excellent agreement with
data assuming that the pion distribution amplitude is
close to its asymptotic form . We also reproduce the
scaling and normalization of the data at large
momentum transfer. Because the renormalization scale is small, we argue that
the effective coupling is nearly constant, thus accounting for the nominal
scaling behavior of the data. However, the normalization of the space-like pion
form factor obtained from electroproduction experiments is
somewhat higher than that predicted by the corresponding commensurate scale
relation. This discrepancy may be due to systematic errors introduced by the
extrapolation of the electroproduction data to the
pion pole.Comment: 22 pages, Latex, 7 Latex figures. Several references added,
discussion of scale fixing revised for clarity. Final version to appear in
Phys. Rev.
Renormalized Effective QCD Hamiltonian: Gluonic Sector
Extending previous QCD Hamiltonian studies, we present a new renormalization
procedure which generates an effective Hamiltonian for the gluon sector. The
formulation is in the Coulomb gauge where the QCD Hamiltonian is renormalizable
and the Gribov problem can be resolved. We utilize elements of the Glazek and
Wilson regularization method but now introduce a continuous cut-off procedure
which eliminates non-local counterterms. The effective Hamiltonian is then
derived to second order in the strong coupling constant. The resulting
renormalized Hamiltonian provides a realistic starting point for approximate
many-body calculations of hadronic properties for systems with explicit gluon
degrees of freedom.Comment: 25 pages, no figures, revte
The Mandelstam-Leibbrandt Prescription in Light-Cone Quantized Gauge Theories
Quantization of gauge theories on characteristic surfaces and in the
light-cone gauge is discussed. Implementation of the Mandelstam-Leibbrandt
prescription for the spurious singularity is shown to require two distinct null
planes, with independent degrees of freedom initialized on each. The relation
of this theory to the usual light-cone formulation of gauge field theory, using
a single null plane, is described. A connection is established between this
formalism and a recently given operator solution to the Schwinger model in the
light-cone gauge.Comment: Revtex, 14 pages. One postscript figure (requires psfig). A brief
discussion of necessary restrictions on the light-cone current operators has
been added, and two references. Final version to appear in Z. Phys.
Towards testing the Maldacena Conjecture with SDLCQ
We consider the Maldacena conjecture applied to the near horizon geometry of
a D1-brane in the supergravity approximation and present numerical results of a
test of the conjecture against the boundary field theory calculation using
supersymmetric discrete light-cone quantization (SDLCQ). We present numerical
results with approximately 1000 times as many states as we previously
considered. These results support the Maldacena conjecture and are within
10-15% of the predicted numerical results in some regions. Our results are
still not sufficient to demonstrate convergence, and, therefore, cannot be
considered to a numerical proof of the conjecture. We present a method for
using a ``flavor'' symmetry to greatly reduce the size of the basis and discuss
a numerical method that we use which is particularly well suited for this type
of matrix element calculation.Comment: 6pp., 2 figures, uses elsart.cl
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