In-medium Pions and Partial Restoration of Chiral Symmetry: a model-independent analysis

Abstract

Exploiting operator relations in QCD, we derive a novel and model-independent formula relating the in-medium quark condensate <bar-q q>* to the decay constant F*_t and the wave function renormalization constant Z* of the pion in the nuclear medium. Evaluating Z* at low density from the iso-scalar pion-nucleon scattering data, it is concluded that the enhanced repulsion of the s-wave isovector pion-nucleusinteraction observed in the deeply bound pionic atoms implies directly the reduction of the in-medium quark condensate. The knowlege of the in-medium pion mass is not necessary to reach this conclusion.

4 pages, Talk given at the Yukawa International Seminar (YKIS) 2006, "New frontiers in QCD -- Exotic hadrons and hadronic matter", Kyoto, Japan, 20 Nov. - 8 Dec. 2006. To be published in Supplemet of Prog. Theor. Phys