The neutrino-induced source in helium shell and r-process neutrosynthesis

The huge neutrino pulse that occurs during the collapse of a massive stellar core, is expected to contribute to the origination of a number of isotopes both of light chemical elements and heavy ones. In particular, evaporation of neutrons from helium nuclei excited by neutrino-nuclear inelastic collisions, may result in the r-process as it was first discussed by Epstein et al. (1988). Here, we consider mainly the possibility to obtain the considerable amount of neutrons owing to the neutrino breakup of helium nuclei. It is shown that, in general, the heating of stellar matter due to the neutrino scattering off electrons and the heat released from the neutrino-helium breakup followed by the thermonuclear reactions should be taken into account. On the base of kinetic network, using all the important reactions up to Z = 8, the main features and the time-dependent character of the neutrino-driven neutron flux are investigated. The time-dependent densities of free neutrons produced in helium breakup, Y_n(t), were used to calculate the r-process nucleosynthesis with another full kinetic network for #propor to#3200 nuclides. It was found that in the case of metal-deficient stars, Z#propor to#0.01 Z_sun, the resulting density of free neutrons seems to be high enough to drive the r-process efficiently under favorable conditions. But it is impossible to obtain a sufficient amount of heavy nuclei in neutrino-induced r-process in a helium shell at radii R>R_c_r#approx#10"9 cm. We speculate that to make the neutrino-induced r-process work efficiently in the shell, one has to invoke nonstandard presupernova models in which helium hopefully is closer to the collapsed core owing for instance, to a large scale mixing or/and rotation and magnetic fields. (orig.)SIGLEAvailable from FIZ Karlsruhe / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekDEGerman

Pulsar recoil due to asymmetry of rotating supernova explosion

Evolution of a binary neutron star system taking into account both gravitational radiation and mass transfer in the system is studied in the point mass approximation. It is shown that effects of accretion from the less massive component lead to well determined final characteristics of the system, almost independent of the initial components' mass ratio, with usage of reasonable assumptions about the values of the Roche lobe radius and stellar radius of the less massive component. Evolution of the system is accompanied by the mass loss from the less massive star and finishes with its explosion, when its mass reaches the lower mass limit of neutron stars (close to 0.1 M_sun). After this explosion the second component leaves the system with values of velocity and rotational period, which are determined almost entirely by the total system mass, M_t. This consideration is applied to a possible scenario of collapsing supernovae (that is, of supernovae type II and probably Ib and Ic) explosion. According to this scenario, collapse of a rotating presupernova core leads to its dynamical instability and fragmentation into two pieces, which form the binary system considered. As stated above, we find that two main values predicted by such a scenario, the pulsar recoil velocity and the pulsar period, depend mainly on the total mass of the collapsing core, and almost do not depend neither on the ratio of masses of these pieces, nor on initial parameters of their orbits, which are determined by the yet uncertain fragmentation process. (orig.)22 refs.Available from TIB Hannover: RR 4697(940) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

The structure of hadrons

Recent experimental results contributing to the understanding of the structure of the nucleon are reviewed. They include the final NMC (#mu#N #-># #mu#X) results on proton and deuteron structure functions; a re-analysis of the CCFR (#nu#Fe#->#lX) data on F_2 and xF_3; new preliminary results from CDF on charge asymmetry in W production, from E866 on Drell-Yan #mu#-pair production and from E706 on prompt photon production. New results from HERA on F_2, on the gluon density at low x, on the charm contribution F_2"c "a"n"t"i "c, on a determination of F_L and on measurements in the very low Q"2 region are discussed. (orig.)Available from TIB Hannover: RA 2999(97-248) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Tau decays

The most recent experimental results of #tau# physics are reviewed. The covered topics include precision measurements of semihadronic #tau# decay and their impact on tau branching ratio budget, the current status of the tau consistency test, a determination of Michel parameters and #tau# neutrino helicity, and upper limits on lepton-number violating #tau# decays. (orig.)Available from TIB Hannover: RA 2999(94-168) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Production of the #eta# meson in nucleon-nucleon collisions

The thesis is structured in the following way. The chapters 2 and 3 are devoted to a detailed theoretical analysis of different channels of the reaction NN#->#NN#eta#, i.e. in pp#->#pp#eta#, pn#->#pn#eta#, and pn#->#d#eta#. In the presented model calculations effects of the NN FSI and ISI are taken into account. Our model analysis suggests that the dominant role in the #eta#-meson production process belongs to the re-scattering mechanism involving the pion exchange. The contributions of other meson exchanges have to be taken into account as well since they have an influence on the magnitude of the cross sections due to interference with the amplitude of the pion exchange. The effects of the nucleon-nucleon final state interaction in the reactions NN#->#NNM are studied in detail in chapter 4. It is shown that the FSI effects are indeed not universal, i.e. they do depend on the mass of the produced meson. This is in contrary to the results of Ref. [19-22] where an universal NN FSI was utilized. Furthermore, it is demonstrated that the reaction amplitude cannot be factorized into the production process and (independent) NN FSI effects if the calculation aims at predicting absolute values of the cross sections. The analysis of ISI effects performed in chapter 2 leads us to the conclusion that ISI effects are not uniform in respect to the exchanges by different mesons. It is stressed that the inclusion of the ISI has a significant impact on the absolute value of the cross sections. It leads to strong reduction of the cross sections. Apart from the investigation of the #eta#-meson production in NN-collisions we present also, in chapter 5, an estimation of the cross sections for a_0(980) meson production in the reaction pn#->#ppa_0"-. (orig.)Available from TIB Hannover: RA 831(4004) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Spin generalization of the Ruijsenaars-Schneider model, non-abelian 2D Toda chain and representations of Sklyanin algebra

Action-angle type variables for spin generalizations of the elliptic Ruijsenaars-Schneider system are constructed. The equations of motion of these systems are solved in terms of Riemann theta-functions. It is proved that these systems are isomorphic to special elliptic solutions of the non-abelian 2D Toda chain. A connection between the finite gap solutions of solitonic equations and representations of the Sklyanin algebra is revealed and discrete analogs of the Lame operators are introduced. A simple way to construct representations of the Sklyanin algebra by difference operators is suggested. (orig.)Available from TIB Hannover: RR 1596(165) / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman

Nonthermal ionization and excitation in Type IIb supernova 1993J

A non-LTE study of Type IIb supernova 1993J in the galaxy M81 accounting for nonthermal ionization and line blocking effects is carried out. Hydrodynamical models and theoretical spectra clearly show that nonthermal ionization and excitation dominate after the second maximum, at day #approx# 30, and play a decisive role in reproducing both a smooth tail of the light curve and an emergence of helium lines in the spectrum similar to those observed. Based on our model of supernova 1993J, we predict that the light curves of Type Ib supernovae should be subject to nonthermal ionization and excitation at earlier times than even that of supernova 1993J. To fit the bolometric and visual light curves of supernova 1993J, an outer layer of #approx# 1 M_sun has to be helium-rich hydrogen shell with a hydrogen mass fraction of #approx# 0.1. The fact that such a distribution of hydrogen results in a characteristic maximum of hydrogen number density at velocity of #approx# 8600 km s"-"1 in the expelled envelope is well consistent with late time observations of H#alpha# emission at epochs of 0.5 - 1 year after the explosion. An emergence of helium lines between day 24 and day 30 illustrated by the evolution of calculated profile of the HeI line #lambda#6678Aa completely fits the spectral observations of supernova 1993J. In our model, the outburst of supernova 1993J is interpreted as the explosion of a #approx# 4 M_sun red supergiant undergoing core collapse and leaving a neutron star in a binary system. The progenitor is supposed to have a helium core mass of #approx# 3 M_sun corresponding to a #approx# 13 M_sun main-sequence star. Supernova 1993J adds evidence to the scenario that Type Ib supernovae originate from moderately massive stars on the main sequence which have lost their hydrogen envelopes in interacting binary systems. It is shown that there are strong arguments in favor of a fundamental similarity between the explosions of Type IIb, Ib, and II-P supernovae. (orig.)Available from TIB Hannover / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman