Table of contents

In the field strength approach to Yang-Mills theories a new class of completely self-dual and anti-self-dual classical SU(3) vacuum solutions is found. These solutions have considerably lower action density than the ones known so far. Some properties of these solutions are discussed.

Dirac brackets for the chiral Schwinger model with chiral constraint are derived perturbatively from the correlation function by the BJL limit method. The results show that the Poisson brackets are not consistent in this theory.

Starting from a three-dimensional reduction of the Bethe-Salpeter equation, a meson exchange pi N model is constructed. The resulting pi N potential includes the direct and exchange nucleon terms, sigma and rho exchanges terms, and direct and exchange Delta terms. Reasonable fits to the pi N low-energy phase shifts are obtained. The constructed meson exchange potential is then used to evaluate rescattering effects in the dipole amplitude E₀₊ of pi ⁰ photoproduction from protons near threshold. The results are close to the most recent Mainz data.

It is shown that three-body models of inclusive inelastic break-up ('break-up fusion', BF), lead to an ambiguity also known in the DWBA description. The use of two formally equivalent representations of the break-up transition amplitude can lead to manifestly different expressions for the BF cross section. The cause of the ambiguity is traced to the many-body effects which are ignored in the three-body model.

Compact formulae for a total 1-loop electromagnetic correction, including the contribution of electromagnetic hadron effects to the deep inelastic scattering of polarized leptons on polarized nucleons in the quark-parton model have been obtained. The cases of longitudinal and transverse nucleon polarization are considered in detail. A thorough numerical calculation of corrections to cross sections and polarization asymmetries at muon (electron) energies over the range of 200-2000 GeV (10-16 GeV) has been made. It has been established that the contribution of corrections to the hadron current considerably affects the behaviour of longitudinal asymmetry, particularly at y to 1 (y is the standard scaling variable). A satisfactory agreement is found between the model calculations of corrections to the lepton current and the phenomenological calculation results, which makes it possible to find the total 1-loop correction within the framework of a common approach.

The method for calculating the scattering of composite particles with several kinds of constituent is studied systematically. The formulae are derived and the method to sort all the Glauber expansion terms into several classes is given. The forms of density functions and the method of treating various kinds of elementary scattering amplitudes are discussed. The method of integration and its analytical expressions are introduced. As examples, the authors calculate the D-D, p-p, p-p and pi -p elastic scatterings. These results are compared with the experimental data.

Proton-³He elastic scattering is studied within the framework of the Glauber approximation at 1 GeV. The short-range correlations and the three-body force effects are studied. These effects are considered through a ground state wavefunction of the target nucleus. The results are discussed and compared with experimental data.

The cross section asymmetry Sigma of the deuteron photodisintegration process d( gamma ,pn) has been measured in the energy range 0.3-1.0 GeV for proton CM angles of 45, 60, 75 and 90 degrees . The data obtained are compared with predictions of the existing theoretical models, based on the conventional approach, as well as with the results of Kharkov multipole analysis which takes into account the contribution of dibaryon resonances. Neither of these theoretical models describes the experimental data satisfactorily.

The cross sections for production of eta nuclei (_eta A) by photons are calculated in the framework of the potential nonrelativistic model. The total cross sections of the gamma +¹²C to p+_eta ¹¹B and delta +¹⁶O to p+_eta ¹⁵N reactions characterized by predominant forward emission of protons are shown to take on the maximum values of 0.4 mu b and 1.5 mu b, respectively, at a 0.75 GeV photon energy. The photoproduction of eta nuclei must give rise to characteristic peaks in the nucleon spectra of the gamma A to pX reactions.

The authors examine the contributions of the conventional sequential mechanism and the pion absorption-emission mechanism for the double charge exchange (DCX) on calcium isotopes. It is shown that by combining these two mechanisms the experimental data for the double isobaric analogue transitions can be reproduced quite well. The predictions for the low energy GS to GS DCX on calcium isotopes are presented.

A model of shape coexistence, based on an intruder pi (h₉2/)² excitation, previously applied to explain low-frequency upbending phenomena in ¹⁷¹Re and ¹⁷²Os, is extended to heavier Os and Re isotopes. A phenomenological three-band mixing analysis of the yrast bands of even Os nuclei and the ⁵/₂⁺(402) and ⁹/₂^-(514) bands of the neighbouring Re isotopes is used to deduce the excitation energies of the proposed intruder configuration as a function of neutron number. These are shown to be qualitatively consistent with an (h₉2/)² excitation. The implications of this model for other nuclei are discussed.

The authors examine the experimental data on partial half lives for alpha decay of heavy even-even nuclei. When presented in the traditional form of Geiger-Nuttall plots (1911) for various isotopic sequences, these data clearly indicate the existence of different linear relations for neutron numbers N above and below the magic value of 126. They present a simple cluster model, employing three fixed parameters, which is able to give an excellent account of all these half lives. In particular, it can reproduce the values for all even-even nuclei having 76<or=Z<or=100 to within a factor of approximately two. An important feature of the model is that it envisages preformed alpha particles in the parent nuclei to be moving in orbits with a large value of a global quantum number. The discontinuity in the Geiger-Nuttall plots at N=126 is then naturally explained by an increase of this global quantum number as the alpha particle is forced into a higher orbit by the shell closure.

Scattering and fusion cross sections are calculated within the molecular particle-core model which describes the outermost bound neutron of ¹⁷O in a basis of eigenstates of the two-centre shell model. The coupled channel calculations include the channels of the elastic scattering of ¹⁷O on ¹²C, the inelastic excitation of ¹⁷O to its first excited ¹/₂⁺ state and the single-neutron transfer to the ¹⁶O+¹³C system. A nuclear Landau-Zener effect, which enhances the inelastic excitation of ¹⁷O from the ground state, generates structures in the calculated elastic, inelastic and transfer cross sections which agree with the experimental data. Fusion cross sections are calculated within the molecular particle-core model by utilizing the representation of the absorption cross section in terms of an integral which folds the imaginary optical potential with the radial density of the scattering wavefunctions solving the coupled equations. Fusion calculations in the experimentally measured energy range of E_cm=7-14 MeV show enhancements due to the explicit treatment of inelastic excitation and transfer of the outermost bound neutron of ¹⁷O.

A molecular (optical) potential is used to describe the general features of the low-energy fusion and elastic scattering cross sections for the astrophysically interesting reactions ¹⁶O+¹⁶O, ¹⁶O+¹²C and ¹²C+¹²C. While the imaginary part of the potential is energy-dependent, the real part is energy-independent and contains an exponential repulsive core. A similar kind of potential has been used earlier to study the ¹²C+¹²C and ¹⁶O+¹⁶O elastic scattering cross sections in the higher energy region. With basically two adjustable parameters determined by fitting the elastic scattering data, good agreement is obtained for the overall shape and magnitude of the fusion cross sections. The low-energy elastic scattering cross sections are also found to be very sensitive to the thickness of the core and the range of the attractive part of the potential.

A number of observations of Cygnus X-3 have been made and evidence has been reported for emission of PeV and TeV gamma rays from this object. The results given by the experimental data include the surprising fact that the number of muons involved in the showers induced by photons is not as small as expected. One way of explaining the observed excess of cosmic-ray muons in the gamma -ray induced showers is to postulate the rapid growth of the photonuclear cross section at energies 10⁴ GeV. The authors examine in some detail the development of proton and gamma showers with full account for the photoproduction cross section. Both the lower and upper limits for the number of muons in gamma -initiated showers with photoproduction are calculated. It is shown that for gamma -initiated showers the number of muons is comparable with that in p showers if the rapid increase of the photoproduction cross section is assumed.

The angular resolution of an extensive air shower array for studies on cosmic sources of ultra-high-energy gamma rays has been determined by most of the experimental groups generally by inter-comparison between sub-arrays, in the absence of the knowledge of any steady and strong discrete source. The sub-arrays have been obtained mostly by dividing the main array into two arrays, one containing the even-numbered detectors and another having the odd-numbered detectors. Using this method the angular resolution of the 24-detector array operated at Ooty during 1984-7 was estimated to be about 1.5 degrees . Recently the Ooty group has reported the detection of four episodes of pulsed emission of ultra-high-energy photons from Her X-1 which have been shown to be phase locked with a period of 1.2357701 s. The authors have made a study of the angular resolution for the Ooty array using this signal from Her X-1 which had a relatively low background. The angular resolution of the array has been determined to be 1.6 degrees +or-0.4 degrees . This is the first direct measurement of angular resolution of an air shower array using a point source of ultra-high-energy photons.

Cosmic ray air shower structure measurements and measurement of density and energy of air shower muons of a wide energy range simultaneously in individual air showers by two magnet spectrographs (MDM approximately 500 GeV c^-1) are presented. The measured muon densities have been used to compare with some of the previous measurements on muon densities in air showers of nearly the same size. The measured muon densities have also been applied for distinguishing between various interaction models and between light and heavier air shower primaries. In the air shower size range 10⁴-10⁶ particles the present measurements do not provide evidence for iron primaries and the different interaction models seem not to be distinguishable by air shower observation.

The authors describe the teaching and implementation of a neural network to estimate the core position and energy of extensive air showers recorded by the South Pole air shower experiment, SPASE. The neural network was found to be approximately 300 times faster than the traditional x² minimization technique previously used and as accurate.

A new approach to simulate gamma ray and proton extensive air showers (EAS) is presented with a detailed treatment of the electromagnetic component. In this method a hybrid Monte Carlo program is constructed which utilizes two existing codes: SHOWERSIM and EGS4. Results for EAS generated by vertical gamma rays and protons with primary energies of 10¹³, 10¹⁴, 10¹⁵ and 10¹⁶ eV are reported for different threshold energies at detection level. Shower size fluctuations, lateral distributions and corresponding fits are presented. Similarities and differences between gamma ray and proton initiated showers are discussed.

The components of the M3Y interaction are expanded as a sum of nine Gaussians over the range 0.1 to 4.0 fm. with an RMS deviation which is better than 2%. These expansions are valuable in the construction of microscopic, antisymmetrized cluster form factors.