научный журнал по физике Ядерная физика ISSN: 0044-0027

IVANOV YU. B., VOSKRESENSKY D.N. — 2014 г.

Within non-equilibrium Greens function technique on the real-time contour and the two-particle irreducible -functional method, a non-equilibrium potential is introduced. It naturally generalizes the conventional thermodynamic potential with which it coincides in thermal equilibrium. Variations of the non-equilibrium potential over respective parameters result in the same quantities as those of the thermodynamic potential but in arbitrary non-equilibrium. In particular, for slightly non-equilibrium inhomogeneous configurations a variation of the non-equilibrium potential over volume is associated with the trace of the non-equilibrium stress tensor. The latter is related to the bulk viscosity. This provides a novel way for evaluation of the bulk viscosity.

MELEZHIK V.S. — 2014 г.

We develop a method for treating different quantum few-body dynamics without traditional partial-wave analysis. The key element of the method is a nondirect product discrete-variable representation (npDVR) we have suggested and developed in application to the time-dependent mutidimensional Schrodinger equations. The method is described here in details and the high efficiency and economy are demonstrated in application to the breakup cross sections of helium ion in collision with proton. We also give a brief review of the results obtained in the frame of the method in low-dimensional few-body physics.

BARRANCO F., BROGLIA R.A., IDINI A., POTEL G., VIGEZZI E. — 2014 г.

Recent data resulting from studies of two-nucleon transfer reaction on Li, analyzed through a unified nuclear-structure-direct-reaction theory have provided strong direct as well as indirect confirmation, through the population of the first excited state of Li and of the observation of a strongly quenched ground state transition, of the prediction that phonon-mediated pairing interaction is the main mechanism binding the neutron halo of the 8.5-ms-lived Li nucleus. In other words, the ground state of Li can be viewed as a neutron Cooper pair bound to the Li core, mainly through the exchange of collective vibration of the core and of the pigmy resonance arizing from the sloshing back and forth of the neutron halo against the protons of the core, the mean field leading to unbound two-particle states, a situation essentially not altered by the bare nucleon–nucleon interaction acting between the halo neutrons. Two-neutron pick-up data, together with data on Li, suggest the existence of a pairing vibrational band based on Li, whose members can be excited with the help of inverse kinematic experiments as was done in the case of reaction. The deviation from harmonicity can provide insight into the workings of medium polarization effects on Cooper-pair nuclear pairing, let alone specific information concering the “rigidity” of the shell closure. Further information concerning these questions is provided by the predicted absolute differential cross sections associated with the reactions (g.s.) and (pv) ( (g.s.)). In particular, concerning this last reaction, predictions of can change by an order of magnitude depending on whether the halo properties associated with the orbital are treated selfconsistently in calculating the ground state correlations of the (pair removal) mode, or not.

BASHKANOV M.A., CLEMENT H., DOROSHKEVICH E.A., PEREZ DEL RIO E., PRICKING A., SKORODKO T. YU., WAGNER G.J. — 2014 г.

Despite the number of inclusive measurements of the pionic fusion reactions, the nature of the ABC effect discovered in 1960 was not completely established. Exclusive measurements of the double-pion-production reactions leading to either fused , and nuclear final states or pairs are analyzed. A significant ABC effect - enhancement in the region of low mass - is found only in the isoscalar channel while in the isovector channels it is small or absent. For the reaction with isovector final state an ABC effect was not observed even at the special kinematic conditions to reproduce a quasi-bound two-proton state. The total cross sections for the and fusion reactions show similar resonance-like energy dependence.

ZHEMCHUGOV E.V. — 2014 г.

decay amplitude is considered and proven to be zero due to properties of polarization vectors and Bose statistics. Triangular diagrams for a pseudoscalar and processes with massive fermions in the loop are explicitely calculated. In the Standard Model axial anomaly vanishes in the sum of these diagrams as boson is mixed with one of the Goldstone bosons.

BEHAIRY K.O., FARID M. EL-AZAB, MAHMOUD ZAKARIA M. M. — 2014 г.

The vector analyzing power and differential cross section for the elastic scattering of He nucleus from polarized protons at 71 MeV/nucleon have been analyzed using the optical model potentials. Different versions of the nuclear potential are constructed using phenomenological potentials and semimicroscopic potentials based upon four different versions of He density and three effective nucleon–nucleon interactions. The effects of density dependence and the sensitivity of the cross sections for interactions have been investigated.

UZIKOV YU. N. — 2014 г.

Formalism for spin observables for production of pseudoscalar, scalar, and vector mesons in collision with formation of the diproton in the final state is considered in model-independent way assuming parity and angular momentum conservation. Production of the pseudoscalar mesons ( ) is described by two spin amplitudes and both of them can be completely determined by measurement of unpolarized cross section , vector analyzing power , and spin-correlation coefficients and . Similar result is obtained for production of scalar mesons ( ). It is shown that measurement of the tensor polarization of the vector meson ) in the reaction in collinear kinematics gives the same information as measurement of the spin-correlation coefficients or .

ACHAKOVSKIY O.I., KAMERDZHIEV S.P., KREWALD S., SAPERSTEIN E.E., SPETH J., TOLOKONNIKOV S.V. — 2014 г.

Phonon coupling (PC) corrections to magnetic moments of odd neighbors of magic and semimagic nuclei are analyzed within the self-consistent Theory of Finite Fermi Systems (TFFS) based on the Energy Density Functional by S. A. Fayans et al. The perturbation theory in is used where is the phonon–particle coupling vertex. A model is developed with separating non-regular PC contributions, the rest is supposed to be regular and included into the standard TFFS parameters. An ansatz is proposed to take into account the so-called tadpole term which ensures the total angular momentum conservation with accuracy. An approximate method is suggested to take into account higher-order terms in . Calculations are carried out for four odd-proton chains, the odd Tl, Bi, In, and Sb ones. Different PC corrections strongly cancel each other. In the result, the total PC correction to the magnetic moment in magic nuclei is, as a rule, negligible. In non-magic nuclei considered it is noticeable and, with only one exception, negative. On average it is of the order of and improves the agreement of the theory with the data. Simultaneously we calculated the gyromagnetic ratios of all low-lying phonons in Pb. For the state it is rather close to the Bohr–Mottelson model prediction whereas for other phonons, two and six positive parity states, the difference from the Bohr–Mottelson values is significant.

AYDIN A., KAPLAN A., OZDOGAN H., TEL E. — 2014 г.

The theoretical photo-neutron cross sections for ( ) reaction have been calculated on Nd rare-earth isotopes at photon energies of 8–23 MeV using the PCROSS, TALYS 1.2, and EMPIRE 3.1 computer codes. TALYS 1.2 two-component exciton model and EMPIRE 3.1 exciton model has been used to calculate the pre-equilibrium photo-neutron cross sections. PCROSS Weisskopf–Ewing model has been used for the reaction equilibrium cross-section calculations. The obtained cross sections have been compared with each other and against the experimental values existing in the EXFOR database. Generally, pre-equilibrium model cross-section calculations are in good agreement with the experimental data for all reactions along the incident photon energy in this study.

LOPEZ-QUELLE M., MARCOS S., NIEMBRO R., SAVUSHKIN L.N. — 2014 г.

The binding energies of several isotopic families are studied within the relativistic Hartree–Fock approximation with the pseudovector coupling for the vertex, to find out a suitable strength for the effective pion tensor force (EPTF). An approximation for determining separately the contributions of the central and tensor forces generated by pion is considered. The results for heavy nuclei indicate that a realistic strength for the EPTF is smaller than a half of that appearing in the OPEP. This conclusion also applies to the results for the single-particle energies. Besides, it has been found that there is a genuine relativistic contribution of the EPTF in nuclear matter which is small but significant.

KARTAVTSEV O.I., MALYKH A.V. — 2014 г.

Overview of the recent advances in description of the few two-component fermions is presented. The model of zero-range interaction is generally considered to discuss the principal aspects of the few-body dynamics. Particular attention is paid to detailed description of two identical fermions of mass and a distinct particle of mass : it turns out that two three-body bound states emerge if mass ratio increases up to the critical value , above which the Efimov effect takes place. The topics considered include rigorous treatment of the few-fermion problem in the zero-range interaction limit, low-dimensional results, the four-body energy spectrum, crossover of the energy spectra for near , and properties of potential-dependent states. At last, enlisted are the problems, whose solution is in due course.

CHULUUNBAATAR O., DERBOV V.L., GOZDZ A., GUSEV A.A., HAI L.L., KRASSOVITSKIY P.M., VINITSKY S.I. — 2014 г.

A model for quantum tunnelling of a cluster comprised of identical particles, interacting via oscillator-type potential, through short-range repulsive barrier potentials is introduced for the first time in symmetrized-coordinate representation and numerically studied in the -wave approximation. A constructive method for symmetrizing or antisymmetrizing the -dimensional harmonic oscillator basis functions in the new symmetrized coordinates with respect to permutations of coordinates of identical particles is described. The effect of quantum transparency, manifesting itself in nonmonotonic resonance-type dependence of the transmission coefficient upon the energy of the particles, their number and the type of their symmetry, is analyzed. It is shown that the total transmission coefficient demonstrates the resonance behavior due to the existence of barrier quasi-stationary states, imbedded in the continuum.

SHEVCHENKO N.V. — 2014 г.

We investigated different properties of the system. First, the near-threshold elastic amplitudes of scattering were calculated from the three-body Alt–Grassberger–Sandhas equations with the coupled channels using four versions of the potentials. The potentials reproduce the very recent SIDDHARTA or older KEK experimental data on kaonic hydrogen, data on scattering and have one- or two-pole structure of the resonance. Second, the -level shifts and widths of kaonic deuterium, corresponding to the results on near-threshold antikaon–deuteron scattering, were calculated. The question of existence of a strong quasi-bound state in the system was also investigated.

CERKASKI M., NAZMITDINOV R.G. — 2014 г.

An algebraic approach is formulated to describe shape transitions of two-fermion systems, confined in a three-dimensional axially-symmetric parabolic potential, in an external magnetic field. The fermion interaction is considered in the form . Explicit algebraic expressions are derived in terms of systems parameters and of the magnetic field strength to trace such transitions in the classical limit.

JOLOS R.V. — 2014 г.

The effects of signature and parity splitting in nuclear spectra and the properties of the chiral bands are analyzed basing on a one-dimensional Schrodinger equation with a double-minimum potential. Rotational bands in odd axial and triaxial nuclei, alternating parity bands in even–even nuclei and the chiral bands in odd–odd nuclei are considered. The results obtained are discussed.

EFROS V.D. — 2014 г.

An approach aimed to extend the applicability range of the nonrelativistic microscopic calculations of electronuclear response functions is reviewed. In the quasielastic peak region these calculations agree with experiment at momentum transfers up to about 0.4 GeV/c, while at higher momentum transfers being beyond 1 GeV/c a disagreement is seen. In view of this, a reference frame where dynamic relativistic corrections are small was employed to calculate the response functions and the results were transformed exactly to the laboratory reference frame. This proved to remove the major part of the disagreement with experiment. All leading-order relativistic corrections to the transition charge operator and to the one-body part of the transition current operator were taken into account in the calculations. Furthermore, a particular model to determine the kinematical inputs of the nonrelativistic calculations was introduced. This model provides the correct relativistic relationship between the reaction final-state energy and the momenta of the knocked-out nucleon and the residual system. The above-mentioned choice of a reference frame in conjunction with this model has led to an even better agreement with experiment.

GARRIDO E., GATTOBIGIO M., KIEVSKY A., ROMERO-REDONDO C., VIVIANI M. — 2014 г.

In this work we investigate the structure and dynamics of small clusters of Helium atoms. We consider bound states of clusters having atoms and continuum states in the three-atom system. Motivated by the fact that the He–He system has a very large scattering length compared to the range of the He–He potential ( ), we propose the use of a soft-core interparticle potential. We use an attractive gaussian potential that reproduces the values of the dimer binding energy and the atom–atom scattering length obtained with one of the widely used He–He interactions, the LM2M2 potential. In addition, we include a repulsive three-body force to reproduce the trimer binding energy. With this model, consisting in the sum of a two- and a three-body potential, we show the spectrum of the four, five, and six-particle systems and phase-shifts and inelasticities in the three-atom system. Comparisons to calculations using realistic He–He potentials are given. In addition some universal relations are explored.

BANERJEE D., KUMAR M., SAHOO S. — 2014 г.

Recently, the first evidence for the decay has been announced by the LHCb Collaboration and the measured branching ratio is in good agreement with the standard model (SM) expectation. It has also reported an upper limit for at 95 confidence level. In this paper, we study the and rare decays in flavor-changing model. Our estimated branching ratios are enhanced from their SM values and provide signals for new physics.

DONG J.M., LOMBARDO U., ZUO W. — 2014 г.

Two superfluid states of nuclear matter, which are supposed to play an important role in neutron stars, are discussed: the first one due to the proton–proton pairing in -equilibrium nuclear matter; the second one due to the anisotropic neutron–neutron pairing in neutron matter. Since the two phases appear at high density of nuclear matter, the three-body forces were added to the pairing interaction and the strong correlation effects in the single-paricle spectrum. The energy gaps, obtained solving the extended BCS equations, significantly deviate from the values without medium effects so as to limit the role of these two superfluid states in the interpretation of phenomena occurring in the neutron-star core.

ALAM N., DEB A., GHOSH D., PAL SITARAM — 2014 г.

In the present work target excitation dependence of the self-similar cascading rate has been studied in detail in the framework of Levy stable law using the experimental data of pions obtained from –AgBr interactions at 350 GeV/ . The Levy indices measured from the analysis fulfill the requirement of the Levy stable region . The study gives an evidence of self-similar cascading mechanism responsible for multiparticle production. The different values of indicate different rates of cascading for different degrees of target excitation. Moreover, the values of universal scaling exponent ( ) obtained from Ginzburg–Landau theory indicate that no clear evidence of second-order phase transition has been found in the interaction.