Scattering of hadrons within an extended linear sigma model

In the low-energy regime, hadrons (instead of quarks and gluons) are the relevant degrees of freedom. Their masses and interactions can be well described by effective approaches to QCD. The extended linear sigma model is an effective model based on chiral and dilatation symmetries (together with their explicit as well as spontaneous breaking). It includes (axial-) vector mesons in addition to (pseudo-) scalar ones, which turns out to be very successful in describing the mass spectrum and decay widths of mesons up to 1.7 GeV. Moreover, including two baryon doublets in the so-called mirror assignment allows for introducing a chirally invariant mass term for baryons as well as the interaction with a low-mass four-quark field, related to the resonance f₀(500). Thus, the mass of the nucleon arises not solely from the chiral condensate, but also from the four-quark condensate. The model has been used to describe elastic and inelastic baryon-baryon interactions and can be used to study meson-baryon and photon-baryon interactions as well. A comparison of the theoretical results with experimental data is shown.