1,398 research outputs found
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
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
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
Mesons on a transverse lattice
The meson eigenstates of the light-cone Hamiltonian in a coarse transverse
lattice gauge theory are investigated. Building upon previous work in pure
gauge theory, the Hamiltonian and its Fock space are expanded in powers of
dynamical fields. In the leading approximation, the couplings appearing in the
Hamiltonian are renormalised by demanding restoration of space-time symmetries
broken by the cut-off. Additional requirements from chiral symmetry are
discussed and difficulties in imposing them from first principles in the
leading approximation are noted. A phenomenological calculation is then
performed, in which chiral symmetry in spontaneously broken form is modelled by
imposing the physical pion-rho mass splitting as a constraint. The light-cone
wavefunctions of the resulting Hamiltonian are used to compute decay constants,
form factors and quark momentum and spin distributions for the pion and rho
mesons. Extensions beyond leading order, and the implications for first
principles calculations, are briefly discussed.Comment: 31 pages, 7 figure
Doing Infrastructural Work: The Role of Boundary Objects in Health Information Infrastructure Projects
By their nature information infrastructures require the co-operation of a broad range of diverse stakeholders and interests in order emerge and evolve over-time. Boundary objects provide a means through which those from different social worlds can collaborate without having to reach a consensus in order to do so. In this article we explore the role of such objects, whose infrastructural properties have often been overlooked. We respond to calls to examine the different types of objects used to elicit feedback from potential users and other stakeholders in complex information system projects. Our focus is specifically on health information systems and in particular those involving the implementation of electronic record systems at a national or regional scale. Such projects are notoriously complex and are frequently marked by a diversity of intentions and lack of agreement. When attempted at a national scale at least, they typically fail to meet intended objectives and projects are often abandoned altogether. We suggest that understanding how different types of boundary object—repositories or ideal types—inhibit infrastructural development can assist in understanding these difficulties and point to ways of better supporting the generativity required for the infrastructuralisaton of complex information system
Equivalence of Two Dimensional QCD and the Matrix Model
We consider two dimensional QCD with the spatial dimension compactified to a
circle. We show that the states in the theory consist of interacting strings
that wind around the circle and derive the Hamiltonian for this theory in the
large limit, complete with interactions. Mapping the winding states into
momentum states, we express this Hamiltonian in terms of a continuous field.
For a gauge group with a background source of Wilson loops, we recover
the collective field Hamiltonian found by Das and Jevicki for the matrix
model, except the spatial coordinate is on a circle. We then proceed to show
that two dimensional QCD with a gauge group can be reduced to a one-
dimensional unitary matrix model and is hence equivalent to a theory of
free nonrelativistic fermions on a circle. A similar result is true for the
group , but the fermions must be modded out by the center of mass
coordinate.Comment: 15 pages, CERN-TH 6843/93, UVA-HET-93-0
A Matrix Integral Solution to [P,Q]=P and Matrix Laplace Transforms
In this paper we solve the following problems: (i) find two differential
operators P and Q satisfying [P,Q]=P, where P flows according to the KP
hierarchy \partial P/\partial t_n = [(P^{n/p})_+,P], with p := \ord P\ge 2;
(ii) find a matrix integral representation for the associated \t au-function.
First we construct an infinite dimensional space {\cal W}=\Span_\BC
\{\psi_0(z),\psi_1(z),... \} of functions of z\in\BC invariant under the action
of two operators, multiplication by z^p and A_c:= z \partial/\partial z - z +
c. This requirement is satisfied, for arbitrary p, if \psi_0 is a certain
function generalizing the classical H\"ankel function (for p=2); our
representation of the generalized H\"ankel function as a double Laplace
transform of a simple function, which was unknown even for the p=2 case,
enables us to represent the \tau-function associated with the KP time evolution
of the space \cal W as a ``double matrix Laplace transform'' in two different
ways. One representation involves an integration over the space of matrices
whose spectrum belongs to a wedge-shaped contour \gamma := \gamma^+ + \gamma^-
\subset\BC defined by \gamma^\pm=\BR_+\E^{\pm\pi\I/p}. The new integrals above
relate to the matrix Laplace transforms, in contrast with the matrix Fourier
transforms, which generalize the Kontsevich integrals and solve the operator
equation [P,Q]=1.Comment: 27 pages, LaTeX, 1 figure in PostScrip
Towards Solving QCD in Light-Cone Quantization -- On the Spectrum of the Transverse Zero Modes for SU(2)
The formalism for a non-abelian pure gauge theory in (2+1) dimensions has
recently been derived within Discretized Light-Cone Quantization, restricting
to the lowest {\it transverse} momentum gluons. It is argued why this model can
be a paradigm for full QCD. The physical vacuum becomes non-trivial even in
light-cone quantization. The approach is brought here to tractable form by
suppressing by hand both the dynamical gauge and the constraint zero mode, and
by performing a Tamm-Dancoff type Fock-space truncation. Within that model the
Hamiltonian is diagonalized numerically, yielding mass spectra and
wavefunctions of the glue-ball states. We find that only color singlets have a
stable and discrete bound state spectrum. The connection with confinement is
discussed. The structure function of the gluons has a shape like . The existence of the continuum limit is verified by deriving a
coupled set of integral equations.Comment: 1 Latex file & 9 Postscript files; tarred, compressed and uuencode
Mesons in the massive Schwinger model on the light-cone
We investigate mesons in the bosonized massive Schwinger model in the
light-front Tamm-Dancoff approximation in the strong coupling region. We
confirm that the three-meson bound state has a few percent fermion six-body
component in the strong coupling region when expressed in terms of fermion
variables, consistent with our previous calculations. We also discuss some
qualitative features of the three-meson bound state based on the information
about the wave function.Comment: 19 pages, RevTex, included 6 figures which are compressed and
uuencode
LGR5 expression in oral epithelial dysplasia and oral squamous cell carcinoma
Objective. LGR5 is pivotal to oral cavity development and is implicated in epithelial malignancy whereby stimulation of LGR5 potentiates canonical Wnt signaling. This investigation tested our hypothesis of a correlation between LGR5 expression and the severity of oral epithelial dysplasia (OED) and oral squamous cell carcinoma (OSCC)
- …