Isoscalar compression modes within fluid dynamic approach - art. no. 064302

We study the nuclear isoscalar monopole and dipole compression modes in nuc lei within the fluid dynamic approach (FDA) with and without the effect of relaxation. For a wide region of the medium and heavy nuclei, the FDA predi cts that the isoscalar giant monopole resonance (ISGMR) and the isoscalar g iant dipole resonance (ISGDR) exhaust about 90% of the corresponding model- independent sum rules. In the case of neglecting the effect of relaxation, the FDA, when adjusted to reproduce the centroid energy E0 of the ISGMR, re sults with centroid energy E1 of the ISGDR which is in agreement with the p redictions of the self-consistent Hartree-Fock random-phase approximation c alculations and the scaling model but significantly larger than the experim ental value. We also show that the FDA leads to the correct hydrodynamic li mit for the ratio (E1/E0)(FDA). FVe find that the ratio (E1/E0)(FDA) depend s on the relaxation time and approaches the preliminary experimental value (E1/E0)(exp) = 1.5+/-0.1 in a short relaxation time limit.