Pion pion interactions and the size of the sigma meson

por Miguel Albaladejo (IFIC)

martes 12 mar. 2013 12:00 → 13:00 Europe/Madrid

Sala Seminarios IFIC (Edf. Institutos de Investigación)

We explore the nature of the sigma meson by studying its size, that we determine from its quadratic scalar radius. This is deduced from the scalar form factor, that we calculate from SU(2) O(p^4) chiral lagrangians, without any ad-hoc free parameter, given the dynamically generated nature of the sigma meson in the pion pion interactions. A small value for the size of the sigma meson is found, which points to a four-quark nature of the latter, rather than to a pion molecule picture. We also calculate the dependence of the sigma meson pole and the quadratic scalar radius on the pion mass, in order to give further meaning to our results. We also study pion pion interactions in a finite volume within two different frameworks that implement chiral dynamics and unitarity, namely, the IAM and the N/D method. We include in the chiral amplitudes the O(p^4) terms, which are explicitly volume dependent, in order to quantify the contribution of these terms, that are exponentially supressed in Luscher's formalism.