952 research outputs found
Probabilities in nonorthogonal basis: Four--quark systems
Four-quark states may exist as colorless meson-meson molecules or compact
systems with two-body colored components. We derive an analytical procedure to
expand an arbitrary four--quark wave function in terms of nonorthogonal color
singlet--singlet vectors. Using this expansion we develop the necessary
formalism to evaluate the probability of physical components with an arbitrary
four-quark wave function. Its application to characterize bound and unbound
four--quark states as meson-meson, molecular or compact systems is discussedComment: Accepted for publication in PR
k-String tensions and the 1/N expansion
We address the question of whether the large-N expansion in pure SU(N) gauge
theories requires that k-string tensions must have a power series expansion in
1/N^2, as in the sine law, or whether 1/N contributions are also allowable, as
in Casimir scaling. We find that k-string tensions may, in fact, have 1/N
corrections, and consistency with the large-N expansion in the open-string
sector depends crucially on an exact cancellation, which we will prove, among
terms involving odd powers of 1/N in particular combinations of Wilson loops.
It is shown how these cancellations are fulfilled, and consistency with the
large-N expansion achieved, in a concrete example, namely, strong-coupling
lattice gauge theory with the heat-kernel action. This is a model which has
both a 1/N^2 expansion and Casimir scaling of the k-string tensions. Analysis
of the closed string channel in this model confirms our conclusions, and
provides further insights into the large-N dependence of energy eigenstates and
eigenvalues.Comment: RevTeX4, 21 pages. Typos corrected, references added, some
discussions expanded; conclusions unchanged. Version to appear on PR
New approach to He charge distribution
We present a study of the He charge distribution based on realistic
nucleonic wave functions and incorporation of the nucleon's quark substructure.
The central depression of the proton point density seen in modern four-body
calculations is too small by itself to lead to a correct description of the
charge distribution. We utilize six-quark structures calculated in the
Chromodielectric Model for N-N interactions, and we find a swelling of the
proton charge distribution as the internucleon distance decreases. These charge
distributions are combined with the He wave function using the Independent
Pair Approximation and two-body distributions generated from Green's Function
Monte Carlo calculations. We obtain a reasonably good fit to the experimental
charge distribution without including meson exchange currents.Comment: 9 pages, LaTeX, 4 figures (Figures 1 and 2 doesn't exist as
postscript files : they are only available on request
On independent sets in purely atomic probability spaces with geometric distribution.
We are interested in constructing concrete independent events in purely atomic probability spaces with geometric distribution. Among other facts we prove that there are uncountable many sequences of independent events
Strange Decays of Nonstrange Baryons
The strong decays of excited nonstrange baryons into the final states Lambda
K, Sigma K, and for the first time into Lambda(1405) K, Lambda(1520) K,
Sigma(1385) K, Lambda K*, and Sigma K*, are examined in a relativized quark
pair creation model. The wave functions and parameters of the model are fixed
by previous calculations of N pi and N pi pi, etc., decays. Our results show
that it should be possible to discover several new negative parity excited
baryons and confirm the discovery of several others by analyzing these final
states in kaon production experiments. We also establish clear predictions for
the relative strengths of certain states to decay to Lambda(1405) K and
Lambda(1520) K, which can be tested to determine if a three-quark model of the
Lambda(1405) K is valid. Our results compare favorably with the results of
partial wave analyses of the limited existing data for the Lambda K and Sigma K
channels. We do not find large Sigma K decay amplitudes for a substantial group
of predicted and weakly established negative-parity states, in contrast to the
only previous work to consider decays of these states into the strange final
states Lambda K and Sigma K.Comment: 25 pages, 8 figures, RevTe
Perturbative Expansion around the Gaussian Effective Action: The Background Field Method
We develop a systematic method of the perturbative expansion around the
Gaussian effective action based on the background field method. We show, by
applying the method to the quantum mechanical anharmonic oscillator problem,
that even the first non-trivial correction terms greatly improve the Gaussian
approximation.Comment: 16 pages, 3 eps figures, uses RevTeX and epsf. Errors in Table 1 are
corrected and new references are adde
NN interaction in a Goldstone boson exchange model
Adiabatic nucleon-nucleon potentials are calculated in a six-quark
nonrelativistic chiral constituent quark model where the Hamiltonian contains a
linear confinement and a pseudoscalar meson (Goldstone boson) exchange
interaction between quarks. Calculations are performed both in a cluster model
and a molecular orbital basis, through coupled channels. In both cases the
potentials present an important hard core at short distances, explained through
the dominance of the [51]_{FS} configuration, but do not exhibit an attractive
pocket. We add a scalar meson exchange interaction and show how it can account
for some middle-range attraction.Comment: 32 pages with 12 eps figures incorporated, RevTeX. Final version
published in PR
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