K^+ production in baryon-baryon and heavy-ion collisions

Kaon production cross sections in nucleon-nucleon, nucleon-delta and delta-delta interactions are studied in a boson exchange model. For the latter two interactions, the exchanged pion can be on-mass shell, only contributions due to a virtual pion are included via the Peierls method by taking into account the finite delta width. With these cross sections and also those for pion-baryon interactions, subthreshold kaon production from heavy ion collisions is studied in the relativistic transport model.