Table of contents

The authors predict the existence of multipion droplets stable with respect to strong interactions (condensed pion balls). They perform the analysis using two different approaches. The first one utilizes the phenomenological information about soft pion interactions. It leads to the conclusion that at least pi ⁰'s may form a multipion bound state. The second approach is based on the generalized sigma -model incorporating chiral symmetry, scale invariance and the trace anomaly. In the mean-field approximation disregarding surface effects, they have found nontopological soliton solutions, pion balls, representing the multipion states. Pion balls may be formed in the course of ultrarelativistic heavy-ion collisions due to the condensation of pions in the regions with suppressed quark and gluon condensates.

A three-body isobar model which satisfies Lorentz invariance and two- and three-body unitarity is used to study the continuum three-pion problem. This model has as input the pi pi amplitudes in the channels with l=0 and l=1. The authors have found that most of the low-lying resonances that decay predominantly into three pions can be explained as being due to the three-body mechanism. The model also predicts resonances with isospin 2. They have calculated the phase shifts of the pi rho system in the channel of the omega resonance.

The ratio R_T of K⁺-¹²C to K⁺-d cross sections has been calculated microscopically using a boson-exchange KN amplitude including a coupling of the sigma , omega and rho fields to the polarization of the nuclear medium. One finds that the mixing of the sigma and omega fields reduces considerably the improvement obtained when the sigma and omega fields are dressed independently.

Excited states have been identified for the first time in the neutron-rich nuclide ¹³⁶Te by observing prompt gamma -rays from ²⁵²Cf spontaneous fission fragments. The technique of triple gamma -ray coincidences was used for the first time in a spontaneous fission study to identify ¹³⁶Te. In addition, new high-spin states in N=84 ¹³⁸Xe (12⁺) and ¹⁴⁰Ba (8⁺) and N=86 ¹⁴⁰Xe (10⁺) have been observed. These provide the first high-spin yrast band systematics for the N=84 isotones.

Attempts to understand the breakdown of the Ellis-Jaffe sum-rule observed by the European Muon Collaboration have led a new insight into the QCD parton model. The authors provide an overview of this work with emphasis on the role of the U(1) axial anomaly. Particular attention is given to the role that future experimental work might play in resolving the key theoretical questions.

Using a recently developed technique, the author reformulates the Abelian chiral Schwinger model as a gauge theory, for all relevant regularization schemes.

The contributions of the W loops to the decay of the Z into three photons and to the scattering of light by light are calculated. The C coefficients of the amplitudes of Z to 3 gamma and gamma gamma to gamma gamma* are shown. They are very useful for checking the authors earlier results.

The exact Dyson-Schwinger equation for the effective gluon mass in the temporal axial gauge is shown to reduce to evaluation of a single two-loop skeleton graph as a consequence of the Slavnov-Taylor-Ward-Takahashi conditions for gauge consistency. Not only does the exact one-loop contribution, comprising almost all previous work, and the entire longitudinal part vanish identically, as previously known, but also the number of independent functions to be self-consistently determined is reduced so that it is no longer necessary to consider the four-gluon vertex function, even at the full two-loop level.

The triangular diagram of Prats (1979) for the reaction p+d to ³He+ gamma is analysed within a relativistic framework. A non-relativistic reduction is carried out and the terms present in Prats' treatment are identified. The normalization of the reaction cross section is discussed and a comparison with the experimental data and with other theoretical models is made.

The off-mass-shell part of the pd to ³He vertex function is fixed by the demand of having only u-spinor contributions to the fermion propagators in the low-energy limit of cross-section calculations. A comparison is made between the results with the appropriate off-mass-shell part included and excluded.

Symmetric intermediate-energy heavy-ion collisions are studied in the Boltzmann-Nordheim-Vlasov theory, where the collision dynamics is determined by the mean field, the Pauli principle, and the NN scattering cross sections. Differences between the parallel-ensemble and full-ensemble approaches are enumerated. The effect of the model equation of state on the transverse momentum transfer is delineated and shown to be dramatically energy dependent. The mass dependence of the transverse momentum transfer, rapidity distribution, and collective flow angle is discussed.

The effect of a mixed target ground state is considered when populating states in an odd-odd nucleus via single-nucleon transfer. Expressions for the spectroscopic strength for stripping and pickup reactions have been derived assuming that the target is described by a combination of Nilsson orbitals and final states are mixed configurations. The mixing causes the transfer strength to be spread out over many levels and, even with moderate mixing amplitudes, states that would not normally be populated can get significant cross sections. The results of Nilsson calculations taking into account Coriolis mixing in both the target and final states are compared with single-nucleon transfer data to ¹⁹⁰Ir. It was found for most levels that configuration mixing in the final state is more important than the effects of a mixed target ground state.

The cross sections of (n,n') and (n,p) reactions at 14 MeV on a range of nuclei are analysed using the theory of Feshbach, Kerman and Koonin. The contributions of the multistep compound and multistep direct processes are evaluated, and the strength of the effective nucleon-nucleon potential determined for both the zero-range and Yukawa potentials.

Photoexcitation of 4.5 h half-life ^115mIn and 56 min half-life ^103mRh isomers by inelastic gamma-ray scattering near threshold and in the giant dipole resonance region has been reviewed. In disagreement with earlier experimental results available in the literature, but in good agreement with our experiments published recently, present calculations indicate that above the photoneutron emission threshold the isomer excitation drops abruptly and remains orders of magnitude smaller than at the threshold, even around resonance maximum.

This work investigates the particle correlation effect on the energy boost of emitted nucleons in HI reactions. Specifically, the authors study the following model process: in the first phase of the nucleus-nucleus collision, a part of the projectile nucleons undergoes two successive collisions. First, they impact on correlated particles (clusters) inside the target. Second, the reflected nucleons collide with the projectile-like remanent. By means of both analytical calculations and BUU simulation methods, the energy spectra and angular distributions of nucleons after such two-step collisions were evaluated. The results show that the particle correlation could lead to a prominent energy boost and a forward-peaked distribution of scattered nucleons.

The performance of the EAS array at Kolar Gold Fields (working since 1984 and upgraded by 1987) is described. The array has been designed to search for sources of ultra high energy (UHE) photons. The array, the data recording and estimation of shower parameters are briefly described. The angular resolution of the array is discussed in detail. The authors demonstrate, using their data, that the shower front is not a plane and derive an expression for the correction to be applied to the observed time delays in each EAS before fitting a plane front. They suggest using an acceptance cone, dependent on the number of timing detectors used to estimate the arrival direction of EAS, for point source searches.