1,345 research outputs found
The design and development of a self-commutating stepper motor
The system discussed adopts a well established and space proven motor, the 'stepper-motor' and shows that with simple commutation techniques it can be operated as a brushless dc motor at high speeds
A Study of Heavy-Light Mesons on the Transverse Lattice
We present results from a study of meson spectra and structure in the limit
where one quark is infinitely heavy. The calculations, based on the framework
of light-front QCD formulated on a transverse lattice, are the first
non-perturbative studies of B-mesons in light-front QCD. We calculate the
Isgur-Wise form factor, light-cone distribution amplitude, the heavy-quark
parton distribution function and the leptonic decay constant of B-mesons.Comment: 5 pages, 3 figures, Revtex, corrected typos, added references,
included moment
The Influence of Higher Fock States in Light-Cone Gauge Theories
In the light-cone Fock state expansion of gauge theories, the influence of
non-valence states may be significant in precision non-perturbative
calculations. In two-dimensional gauge theories, it is shown how these states
modify the behaviour of the light-cone wavefunction in significant ways
relative to endemic choices of variational ansatz. Similar effects in
four-dimensional gauge theories are briefly discussed.Comment: 4 pages, REVTE
Transverse Lattice Approach to Light-Front Hamiltonian QCD
We describe a non-perturbative procedure for solving from first principles
the light-front Hamiltonian problem of SU(N) pure gauge theory in D spacetime
dimensions (D>2), based on enforcing Lorentz covariance of observables. A
transverse lattice regulator and colour-dielectric link fields are employed,
together with an associated effective potential. We argue that the light-front
vacuum is necessarily trivial for large enough lattice spacing, and clarify why
this leads to an Eguchi-Kawai dimensional reduction of observables to
1+1-dimensions in the infinite N limit. The procedure is then tested by
explicit calculations for 2+1-dimensional SU(infinity) gauge theory, within a
first approximation to the lattice effective potential. We identify a scaling
trajectory which produces Lorentz covariant behaviour for the lightest
glueballs. The predicted masses, in units of the measured string tension, are
in agreement with recent results from conventional Euclidean lattice
simulations. In addition, we obtain the potential between heavy sources and the
structure of the glueballs from their light-front wavefunctions. Finally, we
briefly discuss the extension of these calculations to 3+1-dimensions.Comment: 55 pages, uses macro boxedeps.tex, minor corrections in revised
versio
String Spectrum of 1+1-Dimensional Large N QCD with Adjoint Matter
We propose gauging matrix models of string theory to eliminate unwanted
non-singlet states. To this end we perform a discretised light-cone
quantisation of large N gauge theory in 1+1 dimensions, with scalar or
fermionic matter fields transforming in the adjoint representation of SU(N).
The entire spectrum consists of bosonic and fermionic closed-string
excitations, which are free as N tends to infinity. We analyze the general
features of such bound states as a function of the cut-off and the gauge
coupling, obtaining good convergence for the case of adjoint fermions. We
discuss possible extensions of the model and the search for new non-critical
string theories.Comment: 20 pages (7 figures available from authors as postscipt files),
PUPT-134
Glueball calculations in large-N_c gauge theory
We use the light-front Hamiltonian of transverse lattice gauge theory to
compute from first principles the glueball spectrum and light-front
wavefunctions in the leading order of the 1/N_c colour expansion. We find
0^{++}, 2^{++}, and 1^{+-} glueballs having masses consistent with N_c=3 data
available from Euclidean lattice path integral methods. The wavefunctions
exhibit a light-front constituent gluon structure.Comment: 4 pages, 2 figures, uses macro boxedeps.tex, minor corrections in
revised versio
Colour-Dielectric Gauge Theory on a Transverse Lattice
We investigate in some detail consequences of the effective colour-dielectric
formulation of lattice gauge theory using the light-cone Hamiltonian formalism
with a transverse lattice. As a quantitative test of this approach, we have
performed extensive analytic and numerical calculations for 2+1-dimensional
pure gauge theory in the large N limit. Because of Eguchi-Kawai reduction, one
effectively studies a 1+1-dimensional gauge theory coupled to matter in the
adjoint representation. We study the structure of coupling constant space for
our effective potential by comparing with the physical results available from
conventional Euclidean lattice Monte Carlo simulations of this system. In
particular, we calculate and measure the scaling behaviour of the entire
low-lying glueball spectrum, glueball wavefunctions, string tension, asymptotic
density of states, and deconfining temperature. We employ a new hybrid
DLCQ/wavefunction basis in our calculations of the light-cone Hamiltonian
matrix elements, along with extrapolation in Tamm-Dancoff truncation,
significantly reducing numerical errors. Finally we discuss, in light of our
results, what further measurements and calculations could be made in order to
systematically remove lattice spacing dependence from our effective potential a
priori.Comment: 48 pages, Latex, uses macro boxedeps.tex, minor errors corrected in
revised versio
B-Mesons on the Transverse Lattice
We present results from a first study of -mesons that is based on a
transverse lattice formulation of light-front QCD. The shape of the Isgur-Wise
form factor is in very good agreement with experimental data. However, the
calculations yield rather large values for and compared
to contemporary calculations based on other techniques.Comment: invited talk given at CSSM workshop on `Lattice Hadron Physics',
Cairns, July 2001 and at ECT* workshop on `Light-cone Physics: Particles and
String', Trento, Sept. 200
Transverse lattice calculation of the pion light-cone wavefunctions
We calculate the light-cone wavefunctions of the pion by solving the meson
boundstate problem in a coarse transverse lattice gauge theory using DLCQ. A
large-N_c approximation is made and the light-cone Hamiltonian expanded in
massive dynamical fields at fixed lattice spacing. In contrast to earlier
calculations, we include contributions from states containing many gluonic
link-fields between the quarks.The Hamiltonian is renormalised by a combination
of covariance conditions on boundstates and fitting the physical masses M_rho
and M_pi, decay constant f_pi, and the string tension sigma. Good covariance is
obtained for the lightest 0^{-+} state, which we identify with the pion. Many
observables can be deduced from its light-cone wavefunctions.After perturbative
evolution,the quark valence structure function is found to be consistent with
the experimental structure function deduced from Drell-Yan pi-nucleon data in
the valence region x > 0.5. In addition, the pion distribution amplitude is
consistent with the experimental distribution deduced from the pi gamma^* gamma
transition form factor and diffractive dissociation. A new observable we
calculate is the probability for quark helicity correlation. We find a 45%
probability that the valence-quark helicities are aligned in the pion.Comment: 27 pages, 9 figure
String Equations for the Unitary Matrix Model and the Periodic Flag Manifold
The periodic flag manifold (in the Sato Grassmannian context) description of
the modified Korteweg--de Vries hierarchy is used to analyse the translational
and scaling self--similar solutions of this hierarchy. These solutions are
characterized by the string equations appearing in the double scaling limit of
the symmetric unitary matrix model with boundary terms. The moduli space is a
double covering of the moduli space in the Sato Grassmannian for the
corresponding self--similar solutions of the Korteweg--de Vries hierarchy, i.e.
of stable 2D quantum gravity. The potential modified Korteweg--de Vries
hierarchy, which can be described in terms of a line bundle over the periodic
flag manifold, and its self--similar solutions corresponds to the symmetric
unitary matrix model. Now, the moduli space is in one--to--one correspondence
with a subset of codimension one of the moduli space in the Sato Grassmannian
corresponding to self--similar solutions of the Korteweg--de Vries hierarchy.Comment: 21 pages in LaTeX-AMSTe
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