Hc. Chiang et al., Chiral non-perturbative approach to the isoscalar s-wave pi pi interactionin a nuclear medium, NUCL PHYS A, 644(1-2), 1998, pp. 77-92
The s-wave isoscalar amplitude for pi pi scattering in a nuclear medium is
evaluated using a nonperturbative unitary coupled channels method and the s
tandard chiral Lagrangians. The method has proved successful to describe th
e pi pi properties in the scalar-isoscalar channel up to 1.2 GeV, giving ri
se to poles in the t matrix for the f(0)(980) and the sigma. The extension
of the method to the nuclear medium implies not only the renormalization of
the pions in the medium, but also the introduction of interaction terms re
lated to contact terms in the pi N --> pi pi N interaction. Off-shell effec
ts are also shown to be important leading to cancellations which reduce the
coupled channel integral equations to a set of algebraic equations. As the
density increases we find a reduction of strength below the a region and a
certain accumulation of strength at energies around pion threshold. Our re
sults, based on chiral Lagrangians, provide similar results to those obtain
ed with phenomenological models which impose minimal chiral constraints. (C
) 1998 Elsevier Science B.V.