Cetin Savkli

Quark-antiquark bound states in the relativistic spectator formalism

The quark-antiquark bound states are discussed using the relativistic spectator (Gross) equations. A relativistic covariant framework for analyzing confined bound states is developed. The relativistic linear potential developed in an earlier work is proven to give vanishing meson {r_arrow} q + {anti q} decay amplitudes, as required by confinement. The regularization of the singularities in the linear potential that are associated with nonzero energy transfers (i.e. q{sup 2} = 0, q{sup {mu}} {ne} 0) is improved. Quark mass functions that build chiral symmetry into the theory and explain the connection between the current quark and constituent quark masses are introduced. The formalism is applied to the description of pions and kaons with reasonable results.

Polarization observables in vector meson photoproduction

The photoproduction of vector mesons ({rho},{omega},{phi}) is of renewed interest because intense high energy beams of polarized electrons and photons are under development. These beams and also polarized targets make it possible to explore the dynamics of basic baryon structure. As a step toward that goal, an analysis of all possible polarization observables for the case of vector meson photoproduction from a nucleon target is presented. The question of which observables are needed to determine completely the basic photoproduction amplitudes and the relationships between spin observables are addressed. Such theorems are most readily demonstrated by representing all observables as bilinear products of helicity amplitudes and using known properties of Dirac gamma and spin-1 matrices. The general angular dependence of spin observables, especially near thresholds and resonances, is examined for the vector meson case. The criteria for a complete set of observables and the relationships between observables are then presented. {copyright} {ital 1996 The American Physical Society.}

Nonperturbative Dynamics of Scalar Field Theories through the Feynman-Schwinger Representation

We present a summary of results obtained for scalar field theories usingt he Feynman-Schwinger (FSR) approach. Specifically, scalar QED and X2φ theories are considered. The motivation behind the applications discussed in this paper is to use the FSR method as a rigorous tool for testing the quality of commonly used approximations in field theory. Exact calculations in a quenched theory are presented for one-, two-, and three-body bound states. Results obtained indicate that some of the commonly used approximations, such as Bethe-Salpeter ladder summation for bound states and the rainbow summation for one-body problems, produce significantly different results from those obtained from the FSR approach. We find that more accurate results can be obtained using other, simpler, approximation schemes.

Normalization of the covariant three-body bound state vertex function

The normalization condition for the relativistic three nucleon Bethe-Salpeter and Gross bound state vertex functions is derived, for the first time, directly from the three body wave equations. It is also shown that the relativistic normalization condition for the two body Gross bound state vertex function is identical to the requirement that the bound state charge be conserved, proving that charge is automatically conserved by this equation.

The stability of the scalar {chi}{sup 2}{phi} interaction

A scalar field theory with a {chi}{dagger}{chi}{phi} interaction is known to be unstable. Yet it has been used frequently without any sign of instability in standard text book examples and research articles. In order to reconcile these seemingly conflicting results, we show that the theory is stable if the Fock space of all intermediate states is limited to a finite number of {chi}{bar {chi}} loops associated with field {chi} that appears quadradically in the interaction, and that instability arises only when intermediate states include these loops to all orders.

Confinement and the analytic structure of the one body propagator in scalar QED

The authors investigate the behavior of the one body propagator in SQED. The self energy is calculated using three different methods: (1) the simple bubble summation, (2) the Dyson-Schwinger equation, and (3) the Feynman-Schwinger representation. The Feynman-Schwinger representation allows an exact analytical result in the quenched approximation. It is shown that, while the exact result produces a real mass pole for all couplings, the bubble sum and the Dyson-Schwinger approach in rainbow approximation leads to complex mass poles beyond a certain critical coupling. The model exhibits confinement as a basic property of the four-point function without implying a lack of a mass pole in the propagator.

Multipole analysis of spin observables in vector meson photoproduction.

A multipole analysis of vector meson photoproduction is formulated as a generalization of the pseudoscalar meson case. Expansion of spin observables in the multipole basis and behavior of these observables near threshold and resonances are examined. {copyright} {ital 1996 The American Physical Society.}

Autonomic computing for spacecraft ground systems

Autonomic computing for spacecraft ground systems increases the system reliability and reduces the cost of spacecraft operations and software maintenance. In this paper, we present an autonomic computing solution for spacecraft ground systems at NASA Goddard Space Flight Center (GSFC), which consists of an open standard for the message oriented architecture referred to as GMSEC architecture, the GSFC Mission Services Evolution Center, and an autonomic computing tool, Criteria Action Table (CAT). This solution has been used in many upgraded ground systems for NASAs missions, and provides a framework for developing solutions with higher autonomic maturity