abstract

If a solution of the wave equation has a branching point at a null surface, then there are two and only two ways to extend the solution analytically across the null surface: the phase of a null coordinate, assumed zero for positive values of the coordinate, may be chosen \(+\pi \) or \(-\pi \) for negative values of that coordinate. It is shown that in the Minkowski space-time there exists a sufficiently general set of solutions for which the first choice gives negative frequency solutions while the second gives positive frequency solutions. Moreover, the set of solutions having this property can be defined by a construction prescription which remains meaningful in an arbitrary analytic space-time which does not have closed time-like lines and/or other global peculiarities. This allows giving a generally covariant definition to positive frequency solutions of the wave equation.

abstract

In this review an attempt is made to summarize briefly all that is presently known experimentally about hadron–nucleus collisions at high energies. Comparisons with theoretical models are kept to a minimum. However, an outline of some theoretical ideas that have been put forward in interpreting the data is included.

abstract

A survey of high energy nucleus–nucleus experiments performed at the Berkeley Bevalac Facility is presented. Experimental results are divided into the general areas of peripheral and central collisions. Results on projectile and target fragmentation, total cross section measurements, pion and photon production, and charged particle multiplicities are stressed. Recently there have been theoretical predictions concerning the possibility of observing new phenomena such as shock waves, pion condensates or collapsed nuclear matter. Existing data relevant to some of these speculations are discussed. A brief discussion of future developments with high energy nuclear beams is also presented.

abstract

It is shown that the Glauber model, for factorized ground state densities and purely imaginary elastic amplitudes, can be viewed as a consequence of the classical probability calculus used for computing incoherent cross-sections, supplemented with the optical theorem to obtain the coherent effects.

abstract

It is shown that if one takes into account the nucleon–nucleon short range correlations in the target nucleus and the impact parameter distribution of the elementary production processes, the average multiplicities and multiplicity dispersions decrease by \(\sim 10\%\) for light and \(\sim 5\%\) for heavy nuclei.

abstract

The clustering nature of each energy level of the \(^{10}\)B nucleus has been investigated considering admixed wave functions involving higher radial quanta and in an overlap integral formalism. By evaluating the ground state nuclear quadrupole moment a suggested parameter of deformability of the nucleus in that state is estimated from the experimental value.

abstract

The finite Fermi-system theory (FFST) is applied to M1 resonance properties of even spherical nuclei. The absolute and relative contributions of E1, E2 and M1 resonances to the integral \(\gamma \)-ray absorption cross section in the near-threshold region are calculated for \(^{90}\)Zr, \(^{120}\)Sn, \(^{208}\)Pb.