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J. P. Vary

Publications and source records attributed to J. P. Vary.

124 records · Page 7Linked to original sources
arXiv1998

Non-Perturbative Hamiltonian Approaches To Strong Interaction Physics

The theory of the strong interactions, Quantum Chromodynamics (QCD), has been addressed by a variety of non-perturbative techniques over the decades since its introduction. We have investigated Hamiltonian formulations with different quantization methods and approximation schemes. In one method, we utilize light-front coordinates to investigate the role of bosonic zero modes in leading to confinement. In another method we are able to obtain spectra for the mesons and baryons using constituent quark masses but no phenomenological confinement. We survey our principal accomplishments to date and indicate our future directions.

hep-th↗
arXiv1997

Decay constants, semi-leptonic and non-leptonic decays in a Bethe-Salpeter Model

We evaluate the decay constants for the B and $D$ mesons and the form factors for the semileptonic decays of the B meson to $D$ and $D^*$ mesons in a Bethe-Salpeter model. From data we extract $V_{cb}=0.039 \pm 0.002$ from ${\bar B} \to D^* l {\barν} $ and $V_{cb}=0.037 \pm 0.004$ from ${\bar B} \to D l {\barν} $ decays. The form factors are then used to obtain non-leptonic decay partial widths for $ B\to D π(K) $ and $B \to D D (D_s) $ in the factorization approximation.

hep-ph↗
arXiv1997

QCD near the Light Cone

Starting from the QCD Lagrangian, we present the QCD Hamiltonian for near light cone coordinates. We study the dynamics of the gluonic zero modes of this Hamiltonian. The strong coupling solutions serve as a basis for the complete problem. We discuss the importance of zero modes for the confinement mechanism.

hep-th↗
arXiv1996

B --> D(D^*) Form Factors in a Bethe-Salpeter model

We calculate the form factors for the semileptonic decays of the $B$ meson to $D$ and $D^*$ mesons in a Bethe-Salpeter model. We show that our model is consistent with the constraints of Heavy Quark Effective Theory (HQET) and we extract the matrix elements that represent the $1/m_Q$ corrections to the form factors in HQET. With available data, we obtain $V_{cb} $=$ (31.9 \pm 1.4)\times10^{-3}$.

hep-ph↗
arXiv1995

Large-basis shell model studies of light nuclei with a multi-valued G-matrix effective interaction

Large-basis shell model studies of low-lying excitations in light nuclei from 4He to 7Li have been performed with a multi-valued G-matrix effective interaction, as recently suggested by Haxton et al.. Calculations were performed relative to the vacuum (``no core") using very large, separable model spaces containing all excitations with unperturbed energies up to 8\hbarΩ. Using G matrices derived from a new Nijmegen potential, we achieve a very satisfactory description of these excitations.

nucl-th↗
arXiv1995

Renormalization of Effective Hamiltonians

We introduce a way of implementing Wilson renormalization within the context of the theory of effective Hamiltonians. Our renormalization scheme involves manipulations at the level of the generalized $G$--matrix and is independent of any specific kinematics. We show how to calculate the beta function within this context and exhibit our method using simple scale--invariant quantum mechanical systems.

hep-ph↗
arXiv1994

Isgur-Wise Function and $V_{cb}$ from Bethe-Salpeter Equations

We calculate the Isgur-Wise function from the solutions of the Bethe-Salpeter equations. The shape of the Isgur-Wise function thus calculated is a prediction of the Bethe-Salpeter equations and does not depend on undetermined parameters. We develop an analytical approximation to our Isgur-Wise function in the form $ξ( ω) = η[ 1 - \frac{ρ^2}η (ω- 1) + a (ω- 1)^{3/2}]$ where $ρ^2 = 1.279$, $a = .91$, $η= .9942$ and $ω$ is the recoil velocity. The Isgur-Wise function is then used to obtain $V_{cb}$ from the recent experimental data of ${\bar B} \to D^* \ell \barν$ decay. Our best estimate of $V_{cb}$ is $(34.7 \pm 2.5) \times 10^{-3}$, which is comparable to some of the latest estimates in the literature.

hep-ph↗
arXiv1994

Massive Schwinger Model for Small Fermion Mass

We examine QED$_{1+1}$ (the massive Schwinger model) to extend existing perturbation results in $m_f/m_b$, and compare our results with lattice and DLCQ calculations. (Based on a talk presented by J.P. Vary at ``Theory of Hadrons and Light-Front QCD'', Polona Zgorzelisko, Poland, August 1994.)

hep-ph↗
arXiv1994

Auxiliary potential in no-core shell-model calculations

The Lee-Suzuki iteration method is used to include the folded diagrams in the calculation of the two-body effective interaction $v^{(2)}_{\rm eff}$ between two nucleons in a no-core model space. This effective interaction still depends upon the choice of single-particle basis utilized in the shell-model calculation. Using a harmonic-oscillator single-particle basis and the Reid-soft-core {\it NN} potential, we find that $v^{(2)}_{\rm eff}$ overbinds $^4\mbox{He}$ in 0, 2, and $4\hbarΩ$ model spaces. As the size of the model space increases, the amount of overbinding decreases significantly. This problem of overbinding in small model spaces is due to neglecting effective three- and four-body forces. Contributions of effective many-body forces are suppressed by using the Brueckner-Hartree-Fock single-particle Hamiltonian.

nucl-th↗
arXiv1994

Large-space shell-model calculations for light nuclei

An effective two-body interaction is constructed from a new Reid-like $NN$ potential for a large no-core space consisting of six major shells and is used to generate the shell-model properties for light nuclei from $A$=2 to 6. (For practical reasons, the model space is partially truncated for $A$=6.) Binding energies and other physical observables are calculated and compare favorably with experiment.

nucl-th↗
arXiv1994

J-Psi Suppression in Hadron-Nucleus Collisions

We examine the production of J/$Ψ$ mesons in high energy hadron-nucleus collisions using models that account for both the initial state modification of parton distributions in nuclei and the final state interaction of the produced $c\bar c$ pairs. We show that, at the energies of current fixed target experiments, J/$Ψ$ production through quark-antiquark annihilation gives the largest contribution at $x_F > 0.5$, while gluon-gluon fusion dominates the production at smaller $x_F$. The observed J/$Ψ$ suppression at large $x_F$ is directly connected to nuclear shadowing in deeply inelastic scattering. We find that a $6\sim 8$mb $c\bar c$-nucleon cross section is needed to explain the data on J/$Ψ$ suppression if a simple incoherent multiple scattering formalism is used for the final state interactions.

hep-ph↗
arXiv1993

Simple approximation for the starting-energy-independent two-body effective interaction with applications to 6Li

We apply the Lee-Suzuki iteration method to calculate the linked-folded diagram series for a new Nijmegen local NN potential. We obtain an exact starting-energy-independent effective two-body interaction for a multi-shell, no-core, harmonic-oscillator model space. It is found that the resulting effective-interaction matrix elements can be well approximated by the Brueckner G-matrix elements evaluated at starting energies selected in a simple way. These starting energies are closely related to the energies of the initial two-particle states in the ladder diagrams. The ``exact'' and approximate effective interactions are used to calculate the energy spectrum of 6Li in order to test the utility of the approximate form.

nucl-th↗
arXiv1993

Isospin Multiplet Structure in Ultra--Heavy Fermion Bound States

The coupled Bethe--Salpeter bound state equations for a $Q\bar Q$ system, where $Q=(U,D)$ is a degenerate, fourth generation, super--heavy quark doublet, are solved in several ladder approximation models. The exchanges of gluon, Higgs and Goldstone modes in the standard model are calculated in the ultra--heavy quark limit where weak $γ, W^\pm$ and $Z^0$ contributions are negligible. A natural $I=0$ and $I=1$ multiplet pattern is found, with large splittings occuring between the different weak iso--spin states when $M_Q$, the quark masses, are larger than values in the range $0.4 TeV<M_Q<0.8 TeV$, depending on which model is used. Consideration of ultra--heavy quark lifetime constraints and $U-D$ mass splitting constraints are reviewed to establish the plausibility of lifetime and mass degeneracy requirements assumed for this paper.

hep-ph↗
arXiv1993

Minimizing Effective Many-Body Interactions

A simple two-level model is developed and used to test the properties of effective interactions for performing nuclear structure calculations in truncated model spaces. It is shown that the effective many-body interactions sensitively depend on the choice of the single-particle basis and they appear to be minimized when a self- consistent Hartree-Fock basis is used.

nucl-th↗
arXiv1993

Microscopic Calculations of the Spectra of Light Nuclei

We perform large-space shell-model calculations for the low-lying energy spectra of a few light nuclei, $^4\mbox{He}$, $^5\mbox{He}$, $^6\mbox{Li}$ and $^7\mbox{Li}$, in a no-core model space with a realistic effective two-body interaction (Brueckner G-matrix). Our G-matrices are calculated for the Reid-soft-core potential in a harmonic oscillator basis. Single-particle ``-U'' insertions are replaced by two-particle ``-U'' insertions and are included in the G matrix calculations, which sum them to all orders. With the starting energy of the G-matrix chosen to give approximately the experimental binding energy, we obtain nuclear energy spectra which are in reasonable agreement with experiment. We also investigate the dependence of our results on the size of the model space and on the harmonic oscillator basis parameter ($\hbarΩ$).

nucl-th↗