Axial vector form factor of nucleons in a light-cone diquark model

The nucleon axial vector form factor is investigated in a light-cone quark spectator diquark model, in which Melosh rotations are applied to both the quark and vector diquark. It is found that this model gives a very good description of available experimental data and the results have very little dependence on the parameters of the model. The relation between the nucleon axial constant and the anomalous magnetic moment of nucleons is also discussed.Comment: 8 pages, Revtex4, 1 figure, version to be published in Phys. Rev.

Levinson's Theorem for Dirac Particles

Levinson's theorem for Dirac particles constraints the sum of the phase shifts at threshold by the total number of bound states of the Dirac equation. Recently, a stronger version of Levinson's theorem has been proven in which the value of the positive- and negative-energy phase shifts are separately constrained by the number of bound states of an appropriate set of Schr\"odinger-like equations. In this work we elaborate on these ideas and show that the stronger form of Levinson's theorem relates the individual phase shifts directly to the number of bound states of the Dirac equation having an even or odd number of nodes. We use a mean-field approximation to Walecka's scalar-vector model to illustrate this stronger form of Levinson's theorem. We show that the assignment of bound states to a particular phase shift should be done, not on the basis of the sign of the bound-state energy, but rather, in terms of the nodal structure (even/odd number of nodes) of the bound state.Comment: Latex with Revtex, 7 postscript figures (available from the author), SCRI-06109

Assessing system reliability through binary decision diagrams using bayesian techniques.

Binary Decision Diagrams (BDDs) have been shown to be efficient for the numerical evaluation of the reliability of complex systems. They achieve exact results where Fault Tree Analysis could generally produce only bounds. In this paper the approach to systems evaluation using a Bayesian method in conjunction with BDDs is explored. The advantages of the approach are discussed with respect to both efficiency and the ability to deal with dependency within the system in a natural manner. As an illustration a simple pump configuration is considered which features a dependency. The results demonstrate both the flexibility of the approach and the ease of dealing with the additional complexity of dependency

The Proton Spin and the Wigner Rotation

It is shown that in both the gluonic and strange sea explanations of the Ellis-Jaffe sum rule violation discovered by the European Muon Collaboration (EMC), the spin of the proton, when viewed in in its rest reference frame, could by fully provided by quarks and antiquarks within a simple quark model picture, taken into account the relativistic effect from the Wigner rotation.Comment: 13 latex page

Quantization of static space-times

A 4-dimensional Lorentzian static space-time is equivalent to 3-dimensional Euclidean gravity coupled to a massless Klein-field. By canonically quantizing the coupling model in the framework of loop quantum gravity, we obtain a quantum theory which actually describes quantized static space-times. The Kinematical Hilbert space is the product of the Hilbert space of gravity with that of imaginary scalar fields. It turns out that the Hamiltonian constraint of the 2+1 model corresponds to a densely defined operator in the underlying Hilbert space, and hence it is finite without renormalization. As a new point of view, this quantized model might shed some light on a few physical problems concerning quantum gravity.Comment: 14 pages, made a few modifications, added Journal-re

A unifying framework for seed sensitivity and its application to subset seeds

We propose a general approach to compute the seed sensitivity, that can be applied to different definitions of seeds. It treats separately three components of the seed sensitivity problem -- a set of target alignments, an associated probability distribution, and a seed model -- that are specified by distinct finite automata. The approach is then applied to a new concept of subset seeds for which we propose an efficient automaton construction. Experimental results confirm that sensitive subset seeds can be efficiently designed using our approach, and can then be used in similarity search producing better results than ordinary spaced seeds

Primordial nucleosynthesis with a varying fine structure constant: An improved estimate

We compute primordial light-element abundances for cases with fine structure constant alpha different from the present value, including many sources of alpha dependence neglected in previous calculations. Specifically, we consider contributions arising from Coulomb barrier penetration, photon coupling to nuclear currents, and the electromagnetic components of nuclear masses. We find the primordial abundances to depend more weakly on alpha than previously estimated, by up to a factor of 2 in the case of ^7Li. We discuss the constraints on variations in alpha from the individual abundance measurements and the uncertainties affecting these constraints. While the present best measurements of primordial D/H, ^4He/H, and ^7Li/H may be reconciled pairwise by adjusting alpha and the universal baryon density, no value of alpha allows all three to be accommodated simultaneously without consideration of systematic error. The combination of measured abundances with observations of acoustic peaks in the cosmic microwave background favors no change in alpha within the uncertainties.Comment: Phys. Rev. D accepted version; minor changes in response to refere

BPS String Solutions in Non-Abelian Yang-Mills Theories and Confinement

Starting from the bosonic part of N=2 Super QCD with a 'Seiberg-Witten' N=2 breaking mass term, we obtain string BPS conditions for arbitrary semi-simple gauge groups. We show that the vacuum structure is compatible with a symmetry breaking scheme which allows the existence of Z_k-strings and which has Spin(10) -> SU(5) x Z_2 as a particular case. We obtain BPS Z_k-string solutions and show that they satisfy the same first order differential equations as the BPS string for the U(1) case. We also show that the string tension is constant, which may cause a confining potential between monopoles increasing linearly with their distance.Comment: 11 pages, Latex. Minor changes to the text. Final version to appear in Phys. Rev.

Superfluidity vs Bose-Einstein condensation in a Bose gas with disorder

We investigate the phenomenon of Bose-Einstein condensation and superfluidity in a Bose gas at zero temperature with disorder. By using the Diffusion Monte-Carlo method we calculate the superfluid and the condensate fraction of the system as a function of density and strength of disorder. In the regime of weak disorder we find agreement with the analytical results obtained within the Bogoliubov model. For strong disorder the system enters an unusual regime where the superfluid fraction is smaller than the condensate fraction.Comment: 4 pages, 4 Postscript figure

Quasi-Isotropization of the Inhomogeneous Mixmaster Universe Induced by an Inflationary Process

We derive a ``generic'' inhomogeneous ``bridge'' solution for a cosmological model in the presence of a real self-interacting scalar field. This solution connects a Kasner-like regime to an inflationary stage of evolution and therefore provides a dynamical mechanism for the quasi-isotropization of the universe. In the framework of a standard Arnowitt-Deser-Misner Hamiltonian formulation of the dynamics and by adopting Misner-Chitr\`e-like variables, we integrate the Einstein-Hamilton-Jacobi equation corresponding to a ``generic'' inhomogeneous cosmological model whose evolution is influenced by the coupling with a bosonic field, expected to be responsible for a spontaneous symmetry breaking configuration. The dependence of the detailed evolution of the universe on the initial conditions is then appropriately characterized.Comment: 17 pages, no figure, to appear on PR