Fluctuation properties of strength functions associated with giant resonances

Abstract

We performed fluctuation analysis by means of the local scaling dimension for the strength function of the isoscalar (IS) and the isovector (IV) giant quadrupole resonances in $^{40}\mathrm{Ca}$, where the strength functions are obtained by the shell model calculation within up to the $2p2h$ configurations. It is found that at small energy scale, fluctuation of the strength function almost obeys the Gaussian orthogonal ensemble (GOE) random matrix theory limit. On the other hand, we found a deviation from the GOE limit at the intermediate energy scale of about $1.7\phantom{\rule{0.3em}{0ex}}\text{MeV}$ for the IS and at $0.9\phantom{\rule{0.3em}{0ex}}\text{MeV}$ for the IV. The results imply that different types of fluctuations coexist at different energy scales. Detailed analysis strongly suggests that GOE fluctuation at small energy scale is due to the complicated nature of $2p2h$ states and that fluctuation at the intermediate energy scale is associated with the spreading width of the Tamm-Dancoff $1p1h$ states.