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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.
The partial restoration of chiral symmetry in nuclear medium is investigated in a model independent way by exploiting operator relations in QCD. An exact sum rule is derived for the quark condensate valid for all density. This sum rule is simplified
We shed light upon the eta mass in nuclear matter in the context of partial restoration of chiral symmetry, pointing out that the U_{A}(1) anomaly effects causes the eta-eta mass difference necessarily through the chiral symmetry breaking. As a conse
In-medium modification of the eta mass is discussed in the context of partial restoration of chiral symmetry in nuclear medium. We emphasize that the U_A(1) anomaly effects causes the eta-eta mass difference necessarily through the chiral symmetry br
Recent topics on mesons in nuclei are discussed by especially emphasizing the role of the partial restoration of chiral symmetry in the nuclear medium. The spontaneously broken chiral symmetry in vacuum is considered to be incompletely restored in fi
We study theoretically the formation spectra of deeply bound pionic atoms expected to be observed by experiments with high energy resolution at RIBF/RIKEN, and we discuss in detail the possibilities to extract new information on the pion properties a