Selfgravitating Gas Spheres in a Box and Relativistic Clusters: Relation between Dynamical and Thermodynamical Stability

We derive a variational principle for the dynamical stability of a cluster as a gas sphere in a box. Newtonian clusters are always dynamically stable and, for relativistic clusters, the relation between dynamical and thermodynamical instabilities is analyzed. The boundaries between dynamically and thermodynamically stable and unstable models are found numerically for relativistic stellar systems with different cut off parameters. A criterion based on binding energy curve is used for determination of the boundary of dynamical stability.Comment: 10 figure

Effective Regge QCD

A new framework for a high energy limit of quantum gauge field theories is introduced. Its potency is illustrated on a new derivation of the reggeization of the gluon.Comment: Latex, 9 pages + 2 figures as PS-file, extended version, to appear in Phys. Rev. Let

Minimal Family Unification

Absract It is proposed that there exist, within a new $SU(2)^{'}$, a gauged discrete group $Q_6$ (the order 12 double dihedral group) acting as a family symmetry. This nonabelian finite group can explain hierarchical features of families, using an assignment for quarks and leptons dictated by the requirements of anomaly cancellation and of no additional quarks.Comment: 10 pages, IFP-701-UNC;VAND-TH-94-

Estimation of coupling between oscillators from short time series via phase dynamics modeling: limitations and application to EEG data

We demonstrate in numerical experiments that estimators of strength and directionality of coupling between oscillators based on modeling of their phase dynamics [D.A. Smirnov and B.P. Bezruchko, Phys. Rev. E 68, 046209 (2003)] are widely applicable. Namely, although the expressions for the estimators and their confidence bands are derived for linear uncoupled oscillators under the influence of independent sources of Gaussian white noise, they turn out to allow reliable characterization of coupling from relatively short time series for different properties of noise, significant phase nonlinearity of the oscillators, and non-vanishing coupling between them. We apply the estimators to analyze a two-channel human intracranial epileptic electroencephalogram (EEG) recording with the purpose of epileptic focus localization.Comment: 22 pages, 7 figures, the paper is to be published in Chaos, 2005, vol.15, issue 2, see http://chaos.aip.org

Heavy hexaquarks in a chiral constituent quark model

We discuss the stability of hexaquark systems of type uuddsQ (Q=c or b) within a chiral constituent quark model which successfully describes the baryon spectra including the charmed ones. We find these systems highly unstable against strong decays and give a comparison with some of the previous literature.Comment: 17 pages, Late

Variations on the Deuteron

We consider few problems which are related to the deuteron and have simple analytical solution. Relation is found between the deuteron electric quadrupole moment and the $np$-scattering amplitude. The degree of circular polarization of photons is calculated for the radiative capture of longitudinally polarized thermal neutrons. The anapole, electric dipole and magnetic quadrupole moments of the deuteron are calculated.Comment: 14 pages, late

Ground-State Magnetization for Interacting Fermions in a Disordered Potential : Kinetic Energy, Exchange Interaction and Off-Diagonal Fluctuations

We study a model of interacting fermions in a disordered potential, which is assumed to generate uniformly fluctuating interaction matrix elements. We show that the ground state magnetization is systematically decreased by off-diagonal fluctuations of the interaction matrix elements. This effect is neglected in the Stoner picture of itinerant ferromagnetism in which the ground-state magnetization is simply determined by the balance between ferromagnetic exchange and kinetic energy, and increasing the interaction strength always favors ferromagnetism. The physical origin of the demagnetizing effect of interaction fluctuations is the larger number of final states available for interaction-induced scattering in the lower spin sectors of the Hilbert space. We analyze the energetic role played by these fluctuations in the limits of small and large interaction $U$. In the small $U$ limit we do second-order perturbation theory and identify explicitly transitions which are allowed for minimal spin and forbidden for higher spin. These transitions then on average lower the energy of the minimal spin ground state with respect to higher spin. For large interactions $U$ we amplify on our earlier work [Ph. Jacquod and A.D. Stone, Phys. Rev. Lett. 84, 3938 (2000)] which showed that minimal spin is favored due to a larger broadening of the many-body density of states in the low-spin sectors. Numerical results are presented in both limits.Comment: 35 pages, 24 figures - final, shortened version, to appear in Physical Review

Fermions scattering in a three dimensional extreme black hole background

The absorption cross section for scattering of fermions off an extreme BTZ black hole is calculated. It is shown that, as in the case of scalar particles, an extreme BTZ black hole exhibits a vanishing absorption cross section, which is consistent with the vanishing entropy of such object. Additionally, we give a general argument to prove that the particle flux near the horizon is zero. Finally we show that the {\it reciprocal space} introduced previously in \cite{gm} gives rise to the same result and, therefore, it could be considered as the space where the scattering process takes place in an AdS spacetime.Comment: 15 pages, RevTex4. Revised version. To be published in Class. Quantum. Gra

Nucleon Structure and Parity-Violating Electron Scattering

We review the area of strange quark contributions to nucleon structure. In particular, we focus on current models of strange quark vector currents in the nucleon and the associated parity-violating elastic electron scattering experiments from which vector- and axial-vector currents are extractedComment: 40 pages including 7 figures; review article to be published in Int. J. Mod. Phys.

Neutrino Masses in the Supersymmetric Standard Model with Right-Handed Neutrinos and Spontaneous R-Parity Violation

We propose an extension of the supersymmetric standard model with right-handed neutrinos and a singlet Higgs field, and study the neutrino masses in this model. The Majorana masses for the right-handed neutrinos are generated around the supersymmetry breaking scale through the vacuum expectation value of the singlet Higgs field. This model may induce spontaneous R-parity violation via the vacuum expectation value of the right-handed sneutrino. In the case, the effective theory is similar to a bilinear R-parity violating model. There are two sources for the neutrino masses: one is this bilinear R-parity breaking effect, and the other is the ordinary seesaw effect between left- and right-handed neutrinos. Combining these two effects, the hierarchical neutrino mass pattern arises even when the neutrino Yukawa matrices are not hierarchical. We acquire appropriate masses and mixings to explain both the solar and atmospheric neutrino oscillations.Comment: 22pages, RevTeX, 3 ps figures; a reference adde