abstract

A recent discovery by the COBE satellite is presented, and its importance discussed in the context of the physics of the early Universe. The various implications for our understanding of the structure of the Universe are outlined.

abstract

After two full years of physics running the OPAL collaboration has observed and analysed approximately \(5 \times 10^5\) hadronic decays of the Z\(^0\). Many new analyses have been completed since the end of the 1991 physics run, of which three are described in detail. A preliminary study of the electric charge of quark and gluon jets in Z\(^0\) decays is presented. A comprehensive investigation into the value of the strong coupling parameter \(\alpha _s,\,(M_{\rm Z^0})\), using 15 different observables from hadronic Z\(^0\) and \(\tau \) decays, is shown. Event shapes, jet rates and energy correlation are consistently described by the single value \(\alpha _s,\,(M_{\rm Z^0}) = 0.122^{+0.006}_{-0.005}\). The first measurement of two-particle momentum correlations in hadronic Z\(^0\) decays and a comparison of this observable with recent analytic QCD calculations and with Monte Carlo simulations is also described.

abstract

We discuss radiative corrections for interactions in the SSC environment. Based on the theory of Yennie, Frautschi and Suura, we develop appropriate Monte Carlo event generators to compute the background electromagnetic radiation. Our results indicate that multiple-photon effects must be taken into account in the study of SSC physics such as Higgs decay.

abstract

In heavy quark production at large Feynman \(x\) there are two hardness scales, one given by the heavy quark pair mass \(\mathcal {M}^2\) and the other by \({\mit \Lambda }^2_{\rm QCD}/(1 - z)\). When these two scales are comparable, the twist expansion of Perturbative QCD breaks down. We discuss the dynamics in this new QCD limit, where \(\mu ^2 = \mathcal {M}^2(1 - x)\) is held fixed as \(\mathcal {M}^2 \to \infty \). New diagrams are found to contribute, which can enhance the cross section above that expected for leading twist. The heavy quarks are produced by a peripheral scattering on the target of hardness \(\mu ^2\). This leads, in particular, to a nuclear target dependence of \(A^{2/3}\) at small \(\mu \). Qualitatively, the dynamics in the new limit agrees with earlier phenomenological models of “intrinsic” heavy quark production.

abstract

Recent work on the derivation of the nucleon–nucleon potential from interacting solitons is discussed. Solitons emerge from chiral effective theories which represent QCD at low energy. A general introduction is given to such theories, their classical solutions and the inclusion of quantum effects. Results from various studies of the two-soliton interaction are discussed which are largely based on numerical evaluation. After semiclassical quantization via a restricted number of collective coordinates the resulting nucleon–nucleon interaction compares well with phenomenological potentials.