Nc Expansion Research Articles

1/ Nc Expansion and non-leptonic weak decays

1/ Nc Expansion and non-leptonic weak decays

| ΔS| = 1 non-leptonic amplitudes and the 1/ Nc expansion

The application of the 1/ N c expansion to the estimate of weak non-leptonic amplitudes is studied. The formulation is renormalization-group invariant and consistent with chiral symmetry. The problem of matching the short- and long-distance descriptions is properly displayed and evidence is shown for the need of more information beyond that known in these regimes. The matching problem first appears at O(1/ N c), but is important because in the 1/ N c approach the relevant octet enhancement (Δ1 = 1 2 rule) requires large contributions from these O(1/ N c) terms.

Production of String-Loops and Rising of Central Plateau in SPS Collider Region

From the viewpoint that hadronic reactions arise from creation of excited strings, the rising of the central plateau, which has been recently observed in the SPS Collider region, is interpret· ed to be due to the production of string· loops on the excited strings. It is predicted that the central plateau grows up steadily in conjunction with the initial increase of the averaged baryon multiplicity but approaches an asymptotic height at energies much higher than the SPS Collider range. Since the successful operation of the CERN SPS Collider, the experimental studies of hadronic interactions have been undertaken at the energy .fS = 540 GeV (PL 155 TeV Ie). The new data on!5p collisions have exhibited the salient rising of the central plateau in rapidity.!) How can we explain the observed rising in terms of the existing models? From the viewpoint of the topological 1/ Nc expansion,2) the multi-hadron production is considered to take place through two steps.3)- 7) The first step is the creation of some excited strings and the second step consists of independent breakups of the strings. We have two excited strings in the first step for the Pomeron part, which dominates at TeV region.*) Namely, above the ISR energy the central plateau may be ascribed to the fragments of two excited strings which are long enough in rapidity to saturate the central plateau in height for !5P collisions. 3 ) The observed rising accordingly seems to be suggesting a new mechanism for multi-hadron production being disclosed at TeV region. It is therefore very instructive to investigate the possibility that excited strings imply some folded structure. In this paper we propose as such, the mechanism of the string-loop production on excited strings which is brought about at some thresh­ old value and becomes predominant at TeV region, as illustrated in Fig. 1,**) and show that this mechanism gives a consistent description of the experimental features.