Antiparticle excitation effect in the relativistic spin-isospin-dependent response function of nucleus

The spin-isospin-dependent response function of nucleus is studied in the r elativistic formalism. Besides the well-known relativistic particle-hole an d Delta-hole excitations, the antiparticle excitations such as nucleon-anti nucleon, nucleon-antidelta, antinucleon-delta excitations are also taken in to account in the calculation of the response function, and the effect of t he antiparticle excitation is emphasized. The antiparticle excitation enhan ces the response function and its effect to the response function is largel y determined by the cutoff parameter which is introduced by the need of the renormalization. The position of the peak of the Delta-hole resonance is m ainly dominated by short range correlation Landau-Migdal parameter g', and we find g' is about 0.6. The effect of two-nucleon absorption and projectil e-target form factor are also studied.