607 research outputs found
On the effective light-cone QCD-Hamiltonian: Application to the pion and other mesons
The effective interaction between a quark and an anti-quark as obtained
previously with by the method of iterated resolvents is replaced by the
up-down-model and applied to flavor off-diagonal mesons including the positive
pion. The only free parameters are the canonical ones, the coupling constant
and the masses of the quarks.Comment: 11 pages, 4 figures, 2 tables, 22 reference
Light-Front QCD(1+1) Coupled to Adjoint Scalar Matter
We consider adjoint scalar matter coupled to QCD(1+1) in light-cone
quantization on a finite `interval' with periodic boundary conditions. We work
with the gauge group SU(2) which is modified to by the
non-trivial topology. The model is interesting for various nonperturbative
approaches because it is the sector of zero transverse momentum gluons of pure
glue QCD(2+1), where the scalar field is the remnant of the transverse gluon
component. We use the Hamiltonian formalism in the gauge .
What survives is the dynamical zero mode of , which in other theories
gives topological structure and degenerate vacua. With a point-splitting
regularization designed to preserve symmetry under large gauge transformations,
an extra dependent term appears in the current . This is reminiscent
of an (unwanted) anomaly. In particular, the gauge invariant charge and the
similarly regulated no longer commute with the Hamiltonian. We show that
nonetheless one can construct physical states of definite momentum which are
not {\it invariant} under large gauge transformations but do {\it transform} in
a well-defined way. As well, in the physical subspace we recover vanishing {\it
expectation values} of the commutators between the gauge invariant charge,
momentum and Hamiltonian operators. It is argued that in this theory the vacuum
is nonetheless trivial and the spectrum is consistent with the results of
others who have treated the large N, SU(N), version of this theory in the
continuum limit.Comment: LaTex, 13 pages. Submitted to Physics Letters
Theta-Vacuum of the Bosonized Massive Light-Front Schwinger Model
The massive Schwinger model in bosonic representation is quantized on the
light front using the Dirac--Bergmann method. The non-perturbative theta-
vacuum in terms of coherent states of the gauge-field zero mode is derived and
found to coincide with the massless case. On the other hand, the mass term
becomes highly non-linear due to the constrained zero mode of the scalar field.
A non-trivial mixing between the normal-mode and zero-mode sectors of the model
is crucial for the correct calculation of the theta-dependence of the leading
order mass correction to the chiral condensate.Comment: 9 pages, LaTe
Confinement and chiral symmetry breaking via a domainlike mean field
Singular gauge fields in the partition function for QCD can lead to a
domain-like picture for the QCD vacuum by virtue of constraints on quantum
fluctuations at the singularities. With a simple model of hyperspherical
domains with interiors of constant field strength we show that the main
features of gluon condensation and an area law for static quarks can be
realised.The Dirac operator in such a background is exactly soluble. Chirality
properties of the solutions show agreement with recent lattice results.Comment: Contribution to the proceedings of the Workshop on Lattice Hadron
Physics, July 9-18 2001, Cairns, Austalia. 5 pages. Elsevier 2 column style
file include
Effect of Zero Modes on the Bound-State Spectrum in Light-Cone Quantisation
We study the role of bosonic zero modes in light-cone quantisation on the
invariant mass spectrum for the simplified setting of two-dimensional SU(2)
Yang-Mills theory coupled to massive scalar adjoint matter. Specifically, we
use discretised light-cone quantisation where the momentum modes become
discrete. Two types of zero momentum mode appear -- constrained and dynamical
zero modes. In fact only the latter type of modes turn out to mix with the Fock
vacuum. Omission of the constrained modes leads to the dynamical zero modes
being controlled by an infinite square-well potential. We find that taking into
account the wavefunctions for these modes in the computation of the full bound
state spectrum of the two dimensional theory leads to 21% shifts in the masses
of the lowest lying states.Comment: LaTeX with 5 postscript file
Phases of a bilayer Fermi gas
We investigate a two-species Fermi gas in which one species is confined in
two parallel layers and interacts with the other species in the
three-dimensional space by a tunable short-range interaction. Based on the
controlled weak coupling analysis and the exact three-body calculation, we show
that the system has a rich phase diagram in the plane of the effective
scattering length and the layer separation. Resulting phases include an
interlayer s-wave pairing, an intralayer p-wave pairing, a dimer Bose-Einstein
condensation, and a Fermi gas of stable Efimov-like trimers. Our system
provides a widely applicable scheme to induce long-range interlayer
correlations in ultracold atoms.Comment: 5 pages, 5 figures; (v2) stability of trimer is emphasized; (v3)
published versio
Costituent Quark Picture out of QCD in two dimensions - on the Light-Cone
Using DLCQ as a nonperturbative method, we test Fock-space truncations in
by studying the mass spectra of hadrons in colour SU(2) and
SU(3) at finite harmonic resolution . We include states
for mesons and up to states for baryons. With this truncation, we
give `predictions' for the masses of the first five states where finite
effects are minimal.Comment: 13 pages, uses elsart.sty 2 Postscript figures, uses epsf.sty
'elsart.sty' and 'elsart12.sty' are available via anonymous-ftp at
ftp://ftp.tex.ac.uk/tex-archive/macros/latex/contrib/supported/elsevie
Realisation of chiral symmetry in the domain model of QCD
The domain model for the QCD vacuum has previously been developed and shown
to exhibit confinement of quarks and strong correlation of the local chirality
of quark modes and duality of the background domain-like gluon field. Quark
fluctuations satisfy a chirality violating boundary conditions parametrized by
a random chiral angle on the domain. The free energy of an
ensemble of domains depends on through
the logarithm of the quark determinant. Its parity odd part is given by the
axial anomaly. The anomaly contribution to the free energy suppresses
continuous axial U(1) degeneracy in the ground state, leaving only a residual
axial Z(2) symmetry. This discrete symmetry and flavour chiral symmetry in turn are spontaneously broken with a quark
condensate arising due to the asymmetry of the spectrum of Dirac operator. In
order to illustrate the splitting between the from octet pseudoscalar
mesons realised in the domain model, we estimate the masses of light
pseudoscalar and vector mesons.Comment: 27 pages, uses RevTeX, 3 figures. v.2. includes additional references
and comment
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