Low energy pseudoscalar-pseudoscalar interactions in the nonrelativistic quark model

We give a brief introduction to the nonrelativistic quark model and then present results from a coupled‐channel quark model analysis of light‐quark S‐wave pseudoscalar‐pseudoscalar scattering and production processes. Annihilation mixing to s‐channel qq̄ scalar resonances and quark exchange interactions are found to be important. Contributions from the exchange of t‐channel mesons are not required to obtain agreement with the data. Intermeson forces are important in all channels and, in particular, lead to isospin 0 and 1 KK̄ bound states analogous to the deuteron; we identify these with the S* (975) and δ(980) scalar resonances.