In-medium pi pi correlation induced by partial restoration of chiral symmetry - art. no. 011901

We show that both the linear and the nonlinear chiral models give an enhanc ement of the pi pi cross section near the 2 pi threshold in the scalar-isos calar (I=J=0) channel in nuclear matter. The reduction of the chiral conden sate, i.e., the partial chiral restoration in nuclear matter, is responsibl e for the enhancement in both cases. We extract an effective 4 pi -nucleon vertex, which is responsible for the enhancement but has not been considere d in the nonlinear models for in-medium pi pi interaction. The relation of this vertex and a next-to-leading order term in the heavy-baryon chiral Lag rangian L-piN((2)) is also discussed.