Eur. Phys. J. A (2006) 27: 191-198
https://doi.org/10.1140/epja/i2005-10245-5

Hadron Physics

Two-pion production processes, chiral symmetry and NN interaction in the medium

¹ IPN Lyon, IN2P3-CNRS and UCB Lyon I, F-69622, Villeurbanne Cedex, France
² Theory Division, Physics Department, CERN, CH-12111, Geneva, Switzerland

^* e-mail: martini@ipnl.in2p3.fr

Received: 25 July 2005
Accepted: 6 February 2006
Published online: 14 March 2006

Abstract

We study the two-pion propagator in the nuclear medium. This quantity appears in the ππ T-matrix and we show that it also enters the QCD scalar susceptibility. The medium effects on this propagator are due to the influence of the individual nucleon response to a scalar field through their pion clouds. This response is appreciably increased by the nuclear environment. It produces an important convergence effect between the scalar and pseudoscalar susceptibilities, reflecting the reshaping of the scalar strength observed in 2π production experiments. While a large modifications of the σ propagator follows, due to its coupling to two pion states, we show that the NN potential remains instead unaffected.