Abstract
We examine the response of closed-shell nuclei using a renormalized interaction, derived with the Unitary Correlation Operator Method (UCOM) from the Argonne V18 potential, and a second RPA (SRPA) method. The same two-body interaction is used to derive the Hartree–Fock ground state and the SRPA equations. Our results show that the coupling of particle–hole states to higher-order configurations produces sizable effects compared with first-order RPA. A much improved description of the isovector dipole and isoscalar quadrupole resonances is obtained, thanks in part to the more fundamental treatment of the nucleon effective mass offered by SRPA. The present work suggests the prospect of describing giant resonance properties realistically and consistently within SRPA or other extended RPA theories. Self-consistency issues of the present SRPA method and residual three-body effects are pointed out.
Highlights
We examine the response of closed-shell nuclei using a correlated interaction, derived with the Unitary Correlation Operator Method (UCOM) from the Argonne V18 potential, in second Random Phase Approximation (RPA) (SRPA) calculations
second RPA (SRPA) and the UCOM make an interesting combination: can SRPA accommodate more physics than firstorder RPA, it appears suitable for describing long-range correlations (LRC) which are excluded from the UCOM by construction
When based on the HF ground state, the SRPA is not fully self-consistent and symmetry-conserving, contrary to the HF-based RPA, as it misses a class of second-order effects related to ground-state correlations [17,18]
Summary
The quantities of interest are transition strength distributions RF (E) of single-particle operators F † = ij fij a†i aj , RF (E) = | λ|F †|0 |2δ(E − Eλ). When based on the HF ground state, the SRPA is not fully self-consistent and symmetry-conserving, contrary to the HF-based RPA, as it misses a class of second-order effects related to ground-state correlations [17,18]. The diagonal approximation, Eq (4) is used It has been verified, though, that inclusion of the 2p2h couplings does not introduce significant corrections. Note that those couplings constitute higher-order effects and their smallness suggests that corrections beyond second order are not large.
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