Annual Report 2003

    COMPUTATIONAL PHYSICS

In 2003, more than 150 scientific publications, reports at conferences and JINR preprints were published and presented.

Work was done on an improvement of the resulting scattering spectra quality due to the use of the spectrometer resolution during both wavelet filtering and traditional smoothing of the small-angle neutron scattering data. This result leads to a better fitting of the form-factor curve at the next step of data analysis (Fig. 4). Besides, the wavelet analysis permits one to extract and analyze a background (noisy) component and, what is more, to carry out instrumental hardware corrections [4].

Fig. 4. Smoothing window results (1) over "raw" data (2) for "new" (a) and "old" (b) ring detector of YuMO

A new experimental scheme for quantum teleportation of heavy matter was proposed. It was shown that the standard experimental technique of nuclear physics experiment could be successfully applied to teleportation of spin states of atomic nuclei. It was claimed that there are no theoretical prohibitions upon a possibility of a complete Bell measurement, therefore, the implementation of all the four quantum communication channels is at least theoretically possible [5].

Calculation of the cross sections for single ionization of the ground and first excited helium states by relativistic impact of a bare uranium ion of charge Zp = +92 with energy 1 GeV/amu were performed. The uranium ion interaction with the target electrons was discribed by the Lienard-Wiechert potential, within the impact parameter approach. The differential ionization cross section were obtained for electron energies E 37 eV below the n = 2 threshold of the He+ ion. In these calculations the nonrelativistic initial and final two-electron correlated atomic states are obtained by numerical procedures from variational principles [6]. A semirelativistic symmetric eikonal distorted wave model treating the collisions beyond first Born approximation was proposed. This model allows one to estimate two-centre effects in the fast heavy-particle collisions [7].

A global analysis of experimental data on the elastic and inelastic scattering of alpha particles by 90,94Zr nuclei and on the total cross sections for their interaction with these nuclei was performed. The deformation length and the neutron to proton multipole matrix-element ratios for the 2+1 and 3+1 states of the 90,92,94,96Zr nuclei were obtained for various projective species, and a comparative analysis of these quantities was performed. With the aim of revealing the origin of the phase shifts found in that study, experimental data on the inelastic scattering of 35.4, 40.0, 50.1, and 65.0 MeV alpha particles on 90,94Zr nuclei were analyzed on the basis of a unified approach [8].

A heavy fermion model is used to describe the jet production in the interaction of the gluon with the polarized proton. Single-spin asymmetry appears due to the interference of single- and double-gluon exchanges between protons. The lowest and relevant contributions to the single-spin asymmetry may be associated with the partial contribution to the odderon and pomeron intercept, respectively. This information can be obtained in numerical analyses [9].

The nucleus-nucleus eikonal phases were calculated in the Glauber approach using realistic Fermi-type nuclear densities taken from electron scattering data. A special method of solving the inversion problem was suggested for restoring the Woods-Saxon-type optical potential. Comparisons were carried out between both of the restored potentials, the ones fitted to the experimental data, and the respective elastic differential and total reaction cross sections [10].

The elastic form factor of 12C was calculated in the plane-wave Born approximation (BA) and also by accounting for distortions of electron waves in the nuclear Coulomb field both within the High-Energy Approximation (HEA) and by numerically solving the Dirac equation (SDE). The nuclear wave function includes peculiarities associated with the alpha-clusterization and short-range correlations of nucleons. It was shown that these correlations affect form factors at comparably large transfer momenta, where a considerable difference takes place between different schemes of calculations, namely, BA, HEA, and SDE methods. It was concluded that the SDE method was preferable when studying effects on form factors of the short- and middle-range nucleon correlations in nuclei [11].

A method of constructing a time-dependent periodic Hamiltonian was elaborated for which a system of Schr oedinger equations admits analytic solutions. Time-independent soluble problems were transformed into time-dependent ones by a set of unitary time-dependent transformations and a proper choice of initial states. A new class of 2x2 periodic time-dependent Hamiltonians with cyclic solutions was constructed in a closed analytic form. In particular, the periodic time-dependent Hamiltonians were generated whose expectation values for cyclic solutions and spin-expectation values do not depend on time. As a consequence, this approach can be used for modelling quantum dynamic wells and wires with the effect of the particle localization [12].

The intertwining operator technique was applied to difference Schr oedinger equations with operator-valued coefficients. It was shown that these equations appear naturally when a discrete basis was used for solving a multichannel Schr oedinger equation. New families of exactly solvable multichannel Hamiltonians have been found [13].

A passage of fast dimesoatoms through a matter was considered from a quantum-mechanical viewpoint. A set of quantum-kinetic equations for the density matrix elements describing their intrinsic state evolution was derived. It was shown that probabilistic description of internal dynamics of hydrogen-like atoms was impossible even at sufficiently low energies because of the "accidental" degeneracy of their energy levels [14].

The anomalous decays in the framework of the three-flavor Nambu-Jona-Lasinio model, in the vacuum and in quark matter in -equilibrium was studied. It was found that the behavior of the relevant observables essentially reflect manifestation of the partial restoration of chiral symmetry, in nonstrange and strange sectors. The probability of such decays decreases with density, showing that anomalous mesonic interactions are significantly affected by the medium [15].

The behavior of neutral pseudoscalar mesons , and in hot and dense matter was investigated in the framework of the three-flavor Nambu-Jona-Lasinio model. Three different scenarios were considered: zero density and finite temperature, zero temperature and finite density in a flavor asymmetric medium with and without strange valence quarks, and finite temperature and density. The behavior of mesons was analyzed in connection with possible signatures of restoration of symmetries. In the high density region and at zero temperature it has been found that the mass of the increased, the deviation from the mass of the being more pronounced in matter without strange valence quarks [16].

A macroscopic model of the dissipative magnetoelastic dynamics of viscous spin polarized nuclear matter was discussed in the context of seismic activity of a paramagnetic neutron star. The source of the magnetic field of such a star is attributed to Pauli paramagnetism of baryon matter promoted by a seed magnetic field frozen into the star in the process of gravitational collapse of a massive progenitor. Particular attention is given to the effect of shear viscosity of incompressible stellar material on the timing of nonradial torsional magnetoelastic pulsations of the star triggered by starquakes. By accentuating the fact that this kind of vibration is unique to the seismology of a paramagnetic neutron star we show that the high-frequency modes decay faster than the low-frequency modes. The obtained analytic expressions for the period and relaxation time of this mode, in which the magnetic susceptibility and viscosity enter as input parameters, are then quantified by numerical estimates for these parameters taken from early and current works on transport coefficients of dense matter. It is found that the effect of viscosity is crucial for the lifetime of magnetotorsion vibrations but it does not appreciably affect the periods of this seismic mode which fall in the realm of periods of pulsed emission of soft -ray repeaters and anomalous X-ray pulsars - young supermagnetized neutron stars, radiating, according to the magnetar model, at the expense of the magnetic energy release. Finally, we present arguments that the long periodic pulsed emission of these stars in a quiescent regime of radiation can be interpreted as a manifestation of weakly damped seismic magnetotorsion vibrations exhibiting the field-induced spin polarization of baryon matter [17].

A portable universal program complex in C language has been created for symbolic-numeric solving of multivariate polynomial systems with finitely many roots. The complex is based on the original algorithms designed in the sector for converting of the initial system into equivalent another system called involutive and more appropriate for the root finding [18].

Based on the original and highly efficient algorithms a fast C program was developed for computing cohomologies of Lie algebras and Lie superalgebras of vector fields. Such computations are important in analyzing general mathematical features of modern supersymmetric models of particle physics and quantum field theory [19].

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