Retardation effects in the rotating string model

A new method to study the retardation effects in mesons is presented. Inspired from the covariant oscillator quark model, it is applied to the rotating string model in which a non zero value is allowed for the relative time between the quark and the antiquark. This approach leads to a retardation term which behaves as a perturbation of the meson mass operator. It is shown that this term preserves the Regge trajectories for light mesons, and that a satisfactory agreement with the experimental data can be obtained if the quark self-energy contribution is added. The consequences of the retardation on the Coulomb interaction and the wave function are also analyzed.Comment: 4 figure

On two- and three-body descriptions of hybrid mesons

Hybrid mesons are exotic mesons in which the color field is not in its ground state. Their understanding deserves interest from a theoretical point of view, because it is intimately related to nonperturbative aspects of QCD. In this work, we analyze and compare two different descriptions of hybrid mesons, namely a two-body $q\bar q$ system with an excited string, or a three-body $q\bar q g$ system. In particular, we show that the constituent gluon approach is equivalent to an effective excited string in the heavy hybrid sector. Instead of a numerical resolution, we use the auxiliary field technique. It allows to find simplified analytical mass spectra and wave functions, and still leads to reliable qualitative predictions. We also investigate the light hybrid sector, and found a mass for the lightest hybrid meson which is in satisfactory agreement with lattice QCD and other effective models.Comment: 2 figure

Preparing for the Improbable: Safety Incentives and the Price-Anderson Act

The Price-Anderson Act requires commercial nuclear power plants to maintain (approximately) $660 million in off-site accident coverage through two forms of insurance: market-provided private insurance and self-insurance in the form of retrospective assessments of reactor owners. We examine how changes in retrospective assessments influence the safety incentives of nuclear reactor owners. As one would expect, increases in self-insurance premiums increase the incentive to install safety systems more quickly. However, a more important conclusion is that self-insurance premiums as a function of reactor riskiness, rather than equal payments by reactor owners, yield a higher level of safety than under the current law

A dilemma in representing observables in quantum mechanics

There are self-adjoint operators which determine both spectral and semispectral measures. These measures have very different commutativity and covariance properties. This fact poses a serious question on the physical meaning of such a self-adjoint operator and its associated operator measures.Comment: 10 page

Computer-aided Interactive Classification: Applications of VIBE

Tools like the VIBE visualization system permit human analysts to use both an understanding of a data set's content and a recognition of structure that the visualization reveals. But what happens when a database's semantics are hidden from the analyst? What guidelines or heuristics can he or she use to reveal the "correct" underlying structure? Results of two experiments conducted at the University of Pittsburgh support the claim that VIBE analysts can uncover a meaningful clustering even without semantic clues. In one experiment artificial data sets were created in which some of the variables discriminate one or more clusters and the other half contribute only random noise. Variable selection guidelines based on computed discrimination value were used in an attempt to distinguish between the signal and noise variables. In a second experiment, a human analyst's encoding of 714 short phrases to 23 overlapping and inter-related categories was stripped of meaningful titles and relabeled with integers. A VIBE analyst was able to highlight relationships among the 23 categories solely on the basisof co-assignment of the phrases