

FIZIKA B 8 (1999) 4, 505534 NUCLEON STRANGENESS AS THE RESPONSE TO A STRANGENESSSENSITIVE PROBE IN A CLASS OF HADRON MODELSD. KLABUČAR^{a}, K. KUMERIČKI^{a}, B. MELIĆ^{b} and I. PICEK^{a} ^{a}Department of Physics, Faculty of Science, University of Zagreb, Bijenička 32, HR10000 Zagreb, Croatia ^{b}Theoretical Physics Division, "R. Bošković"
Institute, Bijenička 54, HR10000 Zagreb, Croatia Received 21 July 1999; Accepted 25 October 1999On top of its valence quarks, the full nucleon ground state may contain appreciable admixture of s`s pairs already at small momentum transfers. This paper discusses strangeness in the meanfield type of nucleon models, and exemplifies this by explicit calculations in the MIT bag model enriched by the presence of instantons. We calculate the instanton contribution to the strangeness in the MIT bag (on top of the standard contribution to strangeness found in that model). Although we do it in an essentially perturbative way, we present a detailed derivation of the formula expressing nucleon matrix elements of bilinear strange quark operators, in terms of a model valence nucleon state and interactions producing quarkantiquark fluctuations on top of that valence state. We do it in detail to clarify our argument that in the context of the meanfield type of quark models (where a Fock state expansion exists and where the nucleon state can be constructed out of singlequark states), the resulting formula acquires a significance beyond perturbation theory. The derivation combines the usage of the evolution operator containing a strangeness source, and FeynmanHellmann theorem. PACS numbers: 12.90+b, 12.40Aa, 14.20Dh

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