Electromagnetic Gauge Invariance of the Cloudy Bag Model

We examine the question of the gauge invariance of electromagnetic form factors calculated within the cloudy bag model. One of the assumptions of the model is that electromagnetic form factors are most accurately evaluated in the Breit frame. This feature is used to show that gauge invariance is respected in this frame.Comment: 8 pages, RevTex, 1 figure, to be published in Phys. Rev.

Comparison of Nucleon Form Factors from Lattice QCD Against the Light Front Cloudy Bag Model and Extrapolation to the Physical Mass Regime

We explore the possibility of extrapolating state of the art lattice QCD calculations of nucleon form factors to the physical regime. We find that the lattice results can be reproduced using the Light Front Cloudy Bag Model by letting its parameters be analytic functions of the quark mass. We then use the model to extend the lattice calculations to large values of Q^{2} of interest to current and planned experiments. These functions are also used to define extrapolations to the physical value of the pion mass, thereby allowing us to study how the predicted zero in G_{E}(Q^{2})/G_{M}(Q^{2}) varies as a function of quark mass.Comment: 31 pages, 22 figure

Army ants algorithm for rare event sampling of delocalized nonadiabatic transitions by trajectory surface hopping and the estimation of sampling errors by the bootstrap method

The most widely used algorithm for Monte Carlo sampling of electronic transitions in trajectory surface hopping (TSH) calculations is the so-called anteater algorithm, which is inefficient for sampling low-probability nonadiabatic events. We present a new sampling scheme (called the army ants algorithm) for carrying out TSH calculations that is applicable to systems with any strength of coupling. The army ants algorithm is a form of rare event sampling whose efficiency is controlled by an input parameter. By choosing a suitable value of the input parameter the army ants algorithm can be reduced to the anteater algorithm (which is efficient for strongly coupled cases), and by optimizing the parameter the army ants algorithm may be efficiently applied to systems with low-probability events. To demonstrate the efficiency of the army ants algorithm, we performed atom–diatom scattering calculations on a model system involving weakly coupled electronic states. Fully converged quantum mechanical calculations were performed, and the probabilities for nonadiabatic reaction and nonreactive deexcitation (quenching) were found to be on the order of 10^–8. For such low-probability events the anteater sampling scheme requires a large number of trajectories (~10^10) to obtain good statistics and converged semiclassical results. In contrast by using the new army ants algorithm converged results were obtained by running 10^5 trajectories. Furthermore, the results were found to be in excellent agreement with the quantum mechanical results. Sampling errors were estimated using the bootstrap method, which is validated for use with the army ants algorithm

Nuclear Quasi-Elastic Electron Scattering Limits Nucleon Off-Mass Shell Properties

The use of quasi-elastic electron nucleus scattering is shown to provide significant constraints on models of the proton electromagnetic form factor of off-shell nucleons. Such models can be constructed to be consistent with constraints from current conservation and low-energy theorems, while also providing a contribution to the Lamb shift that might potentially resolve the proton radius puzzle in muonic hydrogen. However, observations of quasi-elastic scattering limit the overall strength of the off-shell form factors to values that correspond to small contributions to the Lamb shift.Comment: 11 pages, 2 figures. Resubmission to improve the clarity, and correct possible misconception

A Conceptual Model of Service Quality for the Information Systems Function

This paper is motivated by the need to provide the Information Systems (IS) function with a model of service quality that is theoretically sound and conceptually complete. At present, no such model exists. This means IS researchers and practitioners are forced to use models, and associated measures, developed in other disciplines. One such measure, SERVQUAL, is commonly used although it has been shown to be an insufficient measure of IS service quality. In order to develop better measures of IS service quality, we must first have better models. In an effort to address this issue, a conceptual model of service quality for the IS function is proposed. This model draws on reference discipline research to explain the formation of service quality as the comparison of expectations and perceptions across three factors: service delivery, service product, and service environment