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HK: Physik der Hadronen und Kerne

HK 15: Plenary Session

HK 15.2: Plenarvortrag

Dienstag, 12. März 2002, 14:45–15:15, Plenarsaal

Chiral Extrapolation of Lattice QCD data for Baryon Properties — •Thomas R. Hemmert — Physik Department T39, TU München

QCD should predict basic baryon properties like masses, magnetic moments, form factors, etc. However, these quantities are not accessible in terms of quark-gluon perturbation theory. In this talk we focus on two techniques—Lattice simulations of QCD and Chiral Perturbation Theory (ChPT)—which currently begin to develop significant overlap in addressing such questions. Baryon ChPT has been successfully applied to study the influence of the spontaneously broken chiral symmetry on low energy processes involving pions and nucleons. In the present context we are interested in the explicit breaking of chiral symmetry by the finite (current-) quark masses in low energy baryon observables. Such observables can be calculated in computer simulations on a finite space-time grid—Lattice QCD. However, these simulations are usually not performed with realistic small quark masses as the simulation of full QCD with three light flavors u,d,s is technically quite challenging. For reasons of numerical stability it is standard practice in Lattice QCD to work with sets of quite heavy quark masses and then extrapolate the results to physical quark masses. We will show that ChPT via its built-in explicit breaking of chiral symmetry can provide guidance for this extrapolation procedure that goes beyond the traditionally used linear ansatz. Furthermore, we discuss extensions of standard baryon ChPT to so called (partially-) quenched baryon ChPT that allow to estimate the size of artificial modifications of baryon properties due the use of the “quenching” simplification.