Dual-Regge Approach to High-Energy, Low-Mass Diffraction Dissociation

A dual-Regge model with a nonlinear proton Regge trajectory in the missing mass channel, describing the experimental data on low-mass single diffraction dissociation, is constructed. Predictions for the LHC energies are given.Comment: 14 pages, 12 figure

Symmetry, incommensurate magnetism and ferroelectricity: the case of the rare-earth manganites RMnO3

The complete irreducible co-representations of the paramagnetic space group provide a simple and direct path to explore the symmetry restrictions of magnetically driven ferroelectricity. The method consists of a straightforward generalization of the method commonly used in the case of displacive modulated systems and allows us to determine, in a simple manner, the full magnetic symmetry of a given phase originated from a given magnetic order parameter. The potential ferroic and magneto-electric properties of that phase can then be established and the exact Landau free energy expansions can be derived from general symmetry considerations. In this work, this method is applied to the case of the orthorhombic rare-earth manganites RMnO3. This example will allow us to stress some specific points, such as the differences between commensurate or incommensurate magnetic phases regarding the ferroic and magnetoelectric properties, the possible stabilization of ferroelectricity by a single irreducible order parameter or the possible onset of a polarization oriented parallel to the magnetic modulation. The specific example of TbMnO3 will be considered in more detail, in order to characterize the role played by the magneto-electric effect in the mechanism for the polarization rotation induced by an external magnetic field.Comment: Conference: Aperiodic`0

Ultrastructure of meristem and root cap of pea seedlings under spaceflight conditions

Data of electron microscopic analysis of meristem and root cap of pea seedlings grown aboard the Salyut-6 orbital research station in the Oazis apparatus and in the laboratory are presented. The main morphological and anatomical characteristics of the test and control plants are shown to be similar. At the same time, some differences are found in the structural and functional organization of the experimental cells as compared to the controls. They concern first of all the plastic apparatus, mitochondria and Golgi apparatus. It is assumed that cell function for certain periods of weightlessness on the whole ensures execution of the cytodifferentiation programs genetically determined on the Earth. Biochemical and physiological processes vary rather markedly due to lack of initially rigorous determination

One-particle and collective electron spectra in hot and dense QED and their gauge dependence

The one-particle electron spectrum is found for hot and dense QED and its properties are investigated in comparison with the collective spectrum. It is shown that the one-particle spectrum (in any case its zero momentum limit) is gauge invariant, but the collective spectrum, being qualitatively different, is always gauge dependent. The exception is the case $m,\mu=0$ for which the collective spectrum long wavelength limit demonstrates the gauge invariance as well.Comment: 9 pages, latex, no figure

The ground state properties of the spin-1/2 transverse Ising chain with periodically varying bonds and fields

Using continued fractions we study the ground state properties of the spin-1/2 Ising chain in a transverse field with periodically varying interaction strengths and external fields. We consider in detail the chain having the period of modulation of interactions equals 2 and compare the results obtained with those corresponding to the spin-1/2 isotropic XY chain in a transverse field. In contrast to the behaviour of the transverse XY chain, the transverse Ising chain does not exhibit a step-like magnetization vs. field dependence caused by the alternation of bonds, its susceptibility exhibits a logarithmic singularity at the field determined by interaction strengths, and it is stable with respect to spin-Peierls dimerization.Comment: 11 pages, latex, 4 figure

"Free" Constituent Quarks and Dilepton Production in Heavy Ion Collisions

An approach is suggested, invoking vitally the notion of constituent massive quarks (valons) which can survive and propagate rather than hadrons (except of pions) within the hot and dense matter formed below the chiral transition temperature in course of the heavy ion collisions at high energies. This approach is shown to be quite good for description of the experimentally observed excess in dilepton yield at masses 250 MeV < M < 700 MeV over the prompt resonance decay mechanism (CERES cocktail) predictions. In certain aspects, it looks to be even more successful, than the conventional approaches: it seems to match the data somewhat better at dilepton masses before the two-pion threshold and before the rho-meson peak as well as at higher dilepton masses (beyond the phi-meson one). The approach implies no specific assumptions on the equation of state (EOS) or peculiarities of phase transitions in the expanding nuclear matter.Comment: 13 pages, 3 PNG figures. submitted to Sov. Nucl. Phy

Baxter's Q-operator for the homogeneous XXX spin chain

Applying the Pasquier-Gaudin procedure we construct the Baxter's Q-operator for the homogeneous XXX model as integral operator in standard representation of SL(2). The connection between Q-operator and local Hamiltonians is discussed. It is shown that operator of Lipatov's duality symmetry arises naturally as leading term of the asymptotic expansion of Q-operator for large values of spectral parameter.Comment: 23 pages, Late

NGC 7331: the Galaxy with the Multicomponent Central Region

We present the results of the spectral investigation of the regular Sb galaxy NGC 7331 with the Multi-Pupil Field Spectrograph of the 6m telescope. The absorption-line indices H-beta, Mgb, and are mapped to analyse the properties of the stellar populations in the circumnuclear region of the galaxy. The central part of the disk inside ~3" (200 pc) -- or a separate circumnuclear stellar-gaseous disk as it is distinguished by decoupled fast rotation of the ionized gas -- is very metal-rich, rather young, ~ 2 billion years old, and its solar magnesium-to-iron ratio evidences for a very long duration of the last episode of star formation there. However the gas excitation mechanism now in this disk is shock-like. The star-like nucleus had probably experienced a secondary star formation burst too: its age is 5 billion years, much younger than the age of the circumnuclear bulge. But [Mg/Fe]=+0.3 and only solar global metallicity imply that the nuclear star formation burst has been much shorter than that in the circumnuclear disk. The surrounding bulge is rather old, 9--14 billion years old, and moderately metal-poor. The rotation of the stars and gas within the circumnuclear disk is axisymmetric though its rotation plane may be slightly inclined to the global plane of the galaxy. Outside the circumnuclear disk the gas may experience non-circular motions, and we argue that the low-contrast extended bulge of NGC 7331 is triaxial.Comment: LATEX, 27 pages, + 15 Postscript figures. Accepted to Astronomical Journal, July issu

Momentum Space Integral Equations for Three Charged Particles: Diagonal Kernels

It has been a long-standing question whether momentum space integral equations of the Faddeev type are applicable to reactions of three charged particles, in particular above the three-body threshold. For, the presence of long-range Coulomb forces has been thought to give rise to such severe singularities in their kernels that the latter may lack the compactness property known to exist in the case of purely short-range interactions. Employing the rigorously equivalent formulation in terms of an effective-two-body theory we have proved in a preceding paper [Phys. Rev. C {\bf 61}, 064006 (2000)] that, for all energies, the nondiagonal kernels occurring in the integral equations which determine the transition amplitudes for all binary collision processes, possess on and off the energy shell only integrable singularities, provided all three particles have charges of the same sign, i.e., all Coulomb interactions are repulsive. In the present paper we prove that, for particles with charges of equal sign, the diagonal kernels, in contrast, possess one, but only one, nonintegrable singularity. The latter can, however, be isolated explicitly and dealt with in a well-defined manner. Taken together these results imply that modified integral equations can be formulated, with kernels that become compact after a few iterations. This concludes the proof that standard solution methods can be used for the calculation of all binary (i.e., (in-)elastic and rearrangement) amplitudes by means of momentum space integral equations of the effective-two-body type.Comment: 36 pages, 2 figures, accepted for publication in Phys. Rev.