Collective modes and current-algebraic sum rules in nuclear medium

Abstract

In-medium sum rules following from the chiral charge algebra of QCD are reviewed, and new sum rules are derived. The new sum rules relate the excitations (quantum numbers of a0(980)) to the scalar and isovector densities, and are non-trivial for the isospin-asymmetric medium. We present an extensive illustration of the sum rules with the help of quark matter in the Nambu-Jona-Lasinio model. Collective excitations different from the usual meson branches (spin-isospin sound modes) are shown to contribute significantly to the sum rules and to play a crucial role in the limit of vanishing current quark masses.