11 research outputs found
Deconfinement at finite chemical potential
In a confining, renormalisable, Dyson-Schwinger equation model of two-flavour
QCD we explore the chemical-potential dependence of the dressed-quark
propagator, which provides a means of determining the behaviour of the chiral
and deconfinement order parameters, and low-energy pion observables. We find
coincident, first order deconfinement and chiral symmetry restoration
transitions at \mu_c = 375 MeV. f_\pi is insensitive to \mu until \mu \approx
\mu_0 = 0.7 mu_c when it begins to increase rapidly. m_\pi is weakly dependent
on \mu, decreasing slowly with \mu and reaching a minimum 6% less than its
\mu=0 value at \mu=\mu_0. In a two-flavour free-quark gas at \mu=\mu_c the
baryon number density would be approximately 3 \rho_0, where \rho_0=0.16
fm^{-3}; while in such a gas at \mu_0 the density is \rho_0.Comment: 11 pages, 3 figures, epsfig.sty, elsart.st
Interference Effects in Relativistic Deuteron Electrodisintegration
We extend the relativistic plane--wave impulse approximation formalism to
incorporate a specific class of relativistic interference effects for use in
describing inclusive electrodisintegration of H. The role of these
``exchange'' terms for the various response functions accessible in
parity--conserving and --violating inclusive processes is investigated and
shown, especially for the latter, to have important consequences for
experiment. An extension to a simple quasi--deuteron model is also considered.Comment: 28 pages (latex), 15 figures available upon request, TRI-PP-93-101
and MIT-CTP#224
Effective Hamiltonians with Relativistic Corrections I: The Foldy--Wouthuysen transformation versus the direct Pauli reduction
Two different methods of obtaining ``effective Hamiltonians''
which include relativistic corrections to nonrelativistic calculations are
discussed, the standard Foldy--Wouthuysen transformation and what we call the
``direct Pauli reduction''. We wish to investigate under which circumstances
the two approaches yield the same result. Using a generic interaction with
harmonic time dependence we show that differences in the corresponding
effective S--matrices do arise beyond first--order perturbation theory. We
attribute them to the fact that the use of the direct reduction effective
Hamiltonian involves the additional approximation of neglecting contributions
from the negative--energy intermediate states, an approximation which is
unnecessary in the Foldy--Wouthuysen case as there the Hamiltonian
does not connect positive-- and negative--energy states. We conclude that at
least in the cases where the relativistic Hamiltonian is known, using the
direct Pauli reduction effective Hamiltonian introduces spurious relativistic
effects and therefore the Foldy--Wouthuysen reduction should be preferred.Comment: TRIUMF preprint TRI-PP-93-1
Polarized Deformed Nuclei Studied via Coincidence Polarized Electron Scattering: The case of 21 Ne
Coincidence reactions of the type \svec{A}(\svec{e},e'N)B involving the
scattering of polarized electrons from deformed polarized targets are discussed
within the context of the plane--wave impulse approximation. A general
expression for the polarized spectral function for transitions leaving the
residual nucleus in discrete states is presented. General properties and
angular symmetries exhibited by the polarization observables are discussed in
detail. Results for unpolarized cross sections as well as for polarization
ratios (asymmetries) are obtained for typical quasi--free kinematics. The
dependences of the polarization observables on the bound neutron momentum,
target polarization orientation, nuclear deformation and value of the momentum
transfer are discussed in detail for various different kinematical
situations.Comment: 37 pages in Plain TeX, MIT-CTP-209
Nonperturbative Renormalization and the QCD Vacuum
We present a self consistent approach to Coulomb gauge Hamiltonian QCD which
allows one to relate single gluon spectral properties to the long range
behavior of the confining interaction. Nonperturbative renormalization is
discussed. The numerical results are in good agreement with phenomenological
and lattice forms of the static potential.Comment: 23 pages in RevTex, 4 postscript figure
Matter degrees of freedom and string breaking in Abelian projected quenched SU(2) QCD
In the Abelian projection the Yang--Mills theory contains Abelian gauge
fields (diagonal degrees of freedom) and the Abelian matter fields
(off-diagonal degrees) described by a complicated action. The matter fields are
essential for the breaking of the adjoint string. We obtain numerically the
effective action of the Abelian gauge and the Abelian matter fields in quenched
SU(2) QCD and show that the Abelian matter fields provide an essential
contribution to the total action even in the infrared region. We also observe
the breaking of an Abelian analog of the adjoint string using Abelian
operators. We show that the adjoint string tension is dominated by the Abelian
and the monopole contributions similarly to the case of the fundamental
particles. We conclude that the adjoint string breaking can successfully be
described in the Abelian projection formalism.Comment: 16 pages, 10 figures, 2 table
Adjoint "quarks" on coarse anisotropic lattices: Implications for string breaking in full QCD
A detailed study is made of four dimensional SU(2) gauge theory with static
adjoint ``quarks'' in the context of string breaking. A tadpole-improved action
is used to do simulations on lattices with coarse spatial spacings ,
allowing the static potential to be probed at large separations at a
dramatically reduced computational cost. Highly anisotropic lattices are used,
with fine temporal spacings , in order to assess the behavior of the
time-dependent effective potentials. The lattice spacings are determined from
the potentials for quarks in the fundamental representation. Simulations of the
Wilson loop in the adjoint representation are done, and the energies of
magnetic and electric ``gluelumps'' (adjoint quark-gluon bound states) are
calculated, which set the energy scale for string breaking. Correlators of
gauge-fixed static quark propagators, without a connecting string of spatial
links, are analyzed. Correlation functions of gluelump pairs are also
considered; similar correlators have recently been proposed for observing
string breaking in full QCD and other models. A thorough discussion of the
relevance of Wilson loops over other operators for studies of string breaking
is presented, using the simulation results presented here to support a number
of new arguments.Comment: 22 pages, 14 figure
Casimir scaling of SU(3) static potentials
Potentials between static colour sources in eight different representations
are computed in four dimensional SU(3) gauge theory. The simulations have been
performed with the Wilson action on anisotropic lattices where the renormalised
anisotropies have been determined non-perturbatively. After an extrapolation to
the continuum limit we are able to exclude any violations of the Casimir
scaling hypothesis that exceed 5% for source separations of up to 1 fm.Comment: 12 pages, 10 figures, RevTeX, v2: 1 reference added, more explanation
about advantages of anisotrop