abstract

Constraints on physics beyond the standard model require a preliminary understanding of the interplay between the electroweak and strong interactions. Strong interaction effects are in principle non-negligible below the confining scale. A complementary approach, based on the meson-quark duality and applied on the \(\pi ^+\)–\(\pi ^0\) electromagnetic mass difference and the weak K-decays, confirms this expectation. Using this simple non-perturbative framework, we conclude that the K\(_{\rm L}\)–K\(_{\rm S}\) mass difference, the empirical \(\Delta I = \frac {1}{2}\) rule and the recently measured \(\varepsilon '/\varepsilon \) are consistent with the standard model.

abstract

The present status of complete \(\cal {O}(\alpha ^3_{\rm s})\) QCD corrections to jet production and one hadron inclusive production in hadronic collisions is reported.

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Supersymmetric (SUSY) particle production at HERA (proton (820 (3eV)-electron (30 GeV) collider): (1) \({\rm e}^- {\rm p} \to \tilde {\rm e}^-\tilde {\rm q}{\rm X}\), (2)\({\rm e}^-{\rm p} \to \tilde {\rm e}^-\tilde \gamma {\rm qX}\) and (3)\({\rm e}^-{\rm p} \to \tilde \gamma \tilde \nu {\rm qX}\) are investigated in the framework of the minimal SUSY standard model. Emphasis will be put on how to extract signals by minimizing noises coming from respective background processes. It is also pointed out that the differential left-right asymmetry using longitudinally polarized electron beam gives us useful information on selectrons.

abstract

Search for the top quark in the UA1 experiment in 1988–89 is discussed and preliminary results are given. The analysis is based on 4.6 pb\(^{-1}\) integrated luminosity at the CERN SPS p\(\bar {\rm p}\) collider. The properties of isolated muons produced in association with jets are found to be consistent with the predictions of the minimal Standard Model but no signal for the top quark is observed. An upper limit for the production cross section is determined. From this a lower limit of 61 GeV/\(c^2\) (95% CL) is obtained for the mass of the top quark in a statistical analysis of all data. A similar analysis gives a lower limit of 41 GeV/\(c^2\) for the mass of a fourth generation quark with charge-1/3 (b\('\) quark). The UA2 experiment has obtained in a similar analysis of electron data corresponding to an integrated luminosity of 7.1 pb\(^{-1}\) preliminarily a lower limit of 67 GeV/\(c^2\) for the top mass and 53 GeV/\(c^2\) for the b\('\) quark mass. The CDF experiment at the Fermilab p\(\bar {\rm p}\) collider gives as the result of similar analysis of electron data of integrated luminosity of 4.7 pb\(^{-1}\) a preliminary lower limit of 77 GeV/\(c^2\) for the mass of the top quark.

abstract

Basic problems of formation of large structures in the universe are discussed.

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SN1987A, in the Large Magellanic cloud, was the closest supernova since the 1604 event observed by Kepler. It provided a unique opportunity to verify our theories and comfort our beliefs in quite a variety of domains: Astrophysics (Stellar evolution, conditions prevailing at the star’s explosion), Nuclear Physics (Neutron star formation, Equation of state under extreme conditions, Nucleosynthesis) and Particle physics (Neutrino properties). All these observations strongly confirm our previous ideas on the physical conditions prevailing during the supernova explosions, although the SN1987A event was not exempt of surprises.

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We present an introductory discussion of the Hopfield model for neural networks, together with a new interpretation of Hebb’s learning rule. Using a master equation and the language of spin systems, we then derive an equation describing the approach of any initial pattern towards one of the built in patterns. We conclude with some generalizations like spatial structure and the problem of how to perform invariant pattern recognition.

abstract

Gauge theories defined in higher dimensions can be dimensionally reduced over coset spaces giving definite predictions for the resulting four-dimensional theory. We present the most interesting features of these theories as well as an attempt to construct a model with realistic low energy behavior within this framework.

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We describe the work by the Cracow-LSU collaboration on Chromoelectric and chromomagnetic flux distributions around the static charges. We find that large cancellations between electric and magnetic energy density lead to a narrow flux tube.