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Spin-Isospin Modes in Heavy-Ion Collisions: I: Nuclear Matter at Finite Temperatures

Abstract With a view toward implementation in microscopic transport simulations of heavy-ion collisions, the properties of spin-isospin modes are studied in nuclear matter consisting of nucleons and Δ isobars that interact by the exchange of π and ρ mesons. For a standard p -wave interaction and an effective g ′ short-range interaction, the dispersion relations for the spin-isospin modes, and the associated amplitudes, are calculated at various nuclear densities and temperatures within the random-phase approximation. Quantities of physical interest are then extracted, including the total and partial Δ decay widths and the Δ cross sections in the nuclear medium. The self-consistent inclusion of the Δ width has a strong effect on the Δ cross sections at twice the normal nuclear density, as compared with the result of ignoring the width. Generally, the obtained quantities exhibit a strong density dependence, but are fairly insensitive to the temperature, at least up to T = 25 MeV. Finally, it is described how these in-medium effects may be consistently included in microscopic transport simulations of nuclear collisions, and the improvements over previous approaches are discussed.