33 research outputs found
A Variational Fock-Space Treatment of Quarkonium
The variational method and the Hamiltonian formalism of QCD are used to
derive relativistic, momentum space integral equations for a quark-antiquark
system with an arbitrary number of gluons present. As a first step, the
resulting infinite chain of coupled equations is solved in the nonrelativistic
limit by an approximate decoupling method. Comparison with experiment allows us
to fix the quark mass and coupling constant, allowing for the calculation of
the spectra of massive systems such as charmonium and bottomonium. Studying the
results with and without the nonAbelian terms, we find that the presence of the
nonAbelian factors yields better agreement with the experimental spectra.Comment: TEX, no figure
Bound-State Variational Wave Equation For Fermion Systems In QED
We present a formulation of the Hamiltonian variational method for QED which
enables the derivation of relativistic few-fermion wave equation that can
account, at least in principle, for interactions to any order of the coupling
constant. We derive a relativistic two-fermion wave equation using this
approach. The interaction kernel of the equation is shown to be the generalized
invariant M-matrix including all orders of Feynman diagrams. The result is
obtained rigorously from the underlying QFT for arbitrary mass ratio of the two
fermions. Our approach is based on three key points: a reformulation of QED,
the variational method, and adiabatic hypothesis. As an application we
calculate the one-loop contribution of radiative corrections to the two-fermion
binding energy for singlet states with arbitrary principal quantum number ,
and . Our calculations are carried out in the explicitly covariant
Feynman gauge.Comment: 26 page
Analysis of inter-quark interactions in classical chromodynamics
The QCD gluon equation of motion is solved approximately by means of the
Green function. This solution is used to reformulate the Lagrangian of QCD such
that the gluon propagator appears directly in the interaction terms of the
Lagrangian. The nature of the interactions is discussed. Their coordinate-space
form is presented and analyzed in the static, non-relativistic case.Comment: 10 pages, 1 figure, LaTex2
From the Bethe-Salpeter equation to non-relativistic approaches with effective two-body interactions
It is known that binding energies calculated from the Bethe-Salpeter equation
in ladder approximation can be reasonably well accounted for by an
energy-dependent interaction, at least for the lowest states. It is also known
that none of these approaches gives results close to what is obtained by using
the same interaction in the so-called instantaneous approximation, which is
often employed in non-relativistic calculations. However, a recently proposed
effective interaction was shown to account for the main features of both the
Bethe-Salpeter equation and the energy-dependent approach. In the present work,
a detailed comparison of these different methods for calculating binding
energies of a two-particle system is made. Some improvement, previously
incorporated for the zero-mass boson case in the derivation of the effective
interaction, is also employed for massive bosons. The constituent particles are
taken to be distinguishable and spinless. Different masses of the exchanged
boson (including a zero mass) as well as states with different angular momenta
are considered and the contribution of the crossed two-boson exchange diagram
is discussed. With this respect, the role played by the charge of the exchanged
boson is emphasized. It is shown that the main difference between the
Bethe-Salpeter results and the instantaneous approximation ones are not due to
relativity as often conjectured.Comment: 38 pages, 12 eps figures, uses elsart.cls (included
The nature of the Lambda(1405)
We present here some results supporting the nature of the
resonance as dynamically generated from the meson baryon interaction in coupled
channels and resulting from the superposition of two close-by poles. We find
support for this picture in the reaction,
which shows a different shape than the one obtained from the reaction. We also call the attention to the with in the region, which shows a narrow
peak in the calculations around 1420 MeV. We also report on recent calculations
of the radiative decay of the two states and on reactions to
obtain information on these decay modes. Finally, we present results for the
reaction recently measured at ANKE/COSY and compare
them with theoretical results.Comment: Talk given at the NSTAR2007 Workshop, Bonn September 200
Solitosynthesis of Q-balls
We study the formation of Q-balls in the early universe, concentrating on
potentials with a cubic or quartic attractive interaction. Large Q-balls can
form via solitosynthesis, a process of gradual charge accretion, provided some
primordial charge assymetry and initial ``seed'' Q-balls exist. We find that
such seeds are possible in theories in which the attractive interaction is of
the form , with a light ``Higgs'' mass. Condensate formation
and fragmentation is only possible for masses in the sub-eV range;
these Q-balls may survive untill present.Comment: 9 pages, 1 figur
Radiative decays of decuplet hyperons
We calculate the radiative decay widths of decuplet hyperons in a chiral
constituent quark model including electromagnetic exchange currents between
quarks. Exchange currents contribute significantly to the E2 transition
amplitude, while they largely cancel for the M1 transition amplitude.
Strangeness suppression of the radiative hyperon decays is found to be weakened
by exchange currents. Differences and similarities between our results and
other recent model predictions are discussed.Comment: 11 pages, 1 eps figure, revtex, accepted for publication in Phys.
Rev.
The (1+1)-dimensional Massive sine-Gordon Field Theory and the Gaussian Wave-functional Approach
The ground, one- and two-particle states of the (1+1)-dimensional massive
sine-Gordon field theory are investigated within the framework of the Gaussian
wave-functional approach. We demonstrate that for a certain region of the
model-parameter space, the vacuum of the field system is asymmetrical.
Furthermore, it is shown that two-particle bound state can exist upon the
asymmetric vacuum for a part of the aforementioned region. Besides, for the
bosonic equivalent to the massive Schwinger model, the masses of the one boson
and two-boson bound states agree with the recent second-order results of a
fermion-mass perturbation calculation when the fermion mass is small.Comment: Latex, 11 pages, 8 figures (EPS files
Heuristic Models of Two-Fermion Relativistic Systems with Field-Type Interaction
We use the chain of simple heuristic expedients to obtain perturbative and
exactly solvable relativistic spectra for a family of two-fermionic bound
systems with Coulomb-like interaction. In the case of electromagnetic
interaction the spectrum coincides up to the second order in a coupling
constant with that following from the quantum electrodynamics. Discrepancy
occurs only for S-states which is the well-known difficulty in the bound-state
problem. The confinement interaction is considered too.
PACS number(s): 03.65.Pm, 03.65.Ge, 12.39.PnComment: 16 pages, LaTeX 2.0
Pion and Sigma Polarizabilities and Radiative Transitions
Fermilab E781 plans measurements of gamma-Sigma and -pion
interactions using a 600 GeV beam of Sigmas and pions, and a virtual photon
target. Pion polarizabilities and radiative transitions will be measured in
this experiment. The former can test a precise prediction of chiral symmetry;
the latter for a_1(1260) ----> pi + gamma is important for understanding the
polarizability. The experiment also measures polarizabilities and radiative
transitions for Sigma hyperons. The polarizabilities can test predictions of
baryon chiral perturbation theory. The radiative transitions to the
Sigma*(1385) provide a measure of the magnetic moment of the s-quark. Previous
experimental and theoretical results for gamma-pi and gamma-Sigma interactions
are given. The E781 experiment is described.Comment: 13 pages text (tex), Tel Aviv U. Preprint TAUP 2204-94, uses
Springer-Verlag TEX macro package lecproc.cmm (appended at end of tex file,
following \byebye), which requires extracting lecproc.cmm and putting this
file in your directory in addition to the tex file (mmcd.tex) before tex
processing. lecproc.cmm should be used following instructions and guidelines
available from Springer-Verlag. Submitted to the Proceedings of Workshop on
Chiral Dynamics, Massachusetts Institute of Technology, July 1994, Eds. A.
Bernstein, B. Holstein. Replaced Oct. 4 to add TAUP preprint number. Replaced
Oct. 12 to correct Pb target thickness from 1.3% interaction to 0.3