Effect of Δ potential on the π-/π+ ratio in heavy-ion collisions at intermediate energies

Based on the isospin-dependent Boltzmann-Uehling-Uhlenbeck (IBUU) transport model, effects of the Delta resonance potential on the free n/p and pi(-)/pi(+) ratios in the central collision of Au-197 + Au-197 at beam energies of 200 and 400 MeV/nucleon are studied. It is found that the effect of the Delta potential on the ratio of pre-equilibrium free n/p is invisible. The effect of Delta isovector potential on the kinetic-energy-integrating ratio of pi(-)/pi(+) may be observable only at lower incident beam energies and with stiffer symmetry energy. The strength of the Delta isoscalar potential affects the height of the pi(-)/pi(+) ratio around the Coulomb peak but does not affect the kinetic-energy-integrating ratio pi(-)/pi(+). In heavy-ion collisions at intermediate energies, relating to the question of nonconservation of energy on Delta or pi productions, one can replace the Delta potential by the nucleon isoscalar potential especially when a soft symmetry energy is employed.