Giant and pigmy dipole resonances inHe4,O16,22, a

Abstract

We combine the coupled-cluster method and the Lorentz integral transform for the computation of inelastic reactions into the continuum. We show that the bound-state-like equation characterizing the Lorentz integral transform method can be reformulated based on extensions of the coupledcluster equation-of-motion method, and we discuss strategies for viable numerical solutions. Starting from a chiral nucleon-nucleon interaction at next-to-next-to-next-to-leading order, we compute the giant dipole resonances of 4 He, 16,22 O and 40 Ca, truncating the coupled-cluster equation-of-motion method at the two-particle-two-hole excitation level. Within this scheme, we find a low-lying E1 strength in the neutron-rich 22 O nucleus, which compares fairly well with data from [Leistenschneider et al. Phys. Rev. Lett. 86, 5442 (2001)]. We also compute the electric dipole polariziability in 40 Ca. Deficiencies of the employed Hamiltonian lead to overbinding, too small charge radii and a too small electric dipole polarizability in 40 Ca.

Electric dipole polarizability: from few- to many-body systems

“…Moreover, the convergence with respect to the number of Lanczos coefficients used in Eq. (5) is much faster than the one observed for the response function in [4]. Already with 15 Lanczos coefficients the error with respect to the converged value is 0.3%, which shows the advantage of using directly Eq.…”

“…This equation is obtained using the Lorentz integral transform method [6] in the coupled-cluster formulation [4,7]. Similarly to what was done in [8,9], the polarizability can be expressed as a continued fraction of the Lanczos coefficients [10] …”

“…In the coupled-cluster formalism [4] the dipole response function is whereΘ is the dipole excitation operator,T is the cluster operator defined in coupled-cluster theory [5], and 0 L |, |0 R ( n L |, |n R ) are the left and right reference ground states (excited states), respectively. Using Eq.…”

“…In Figure 1, we show the electric dipole polarizability of 4 He as a function of the model space size N max . The green band represents the combined experimental values from [13,14] which have been extracted by fitting to experimental photo-absorption data [15,16].…”

“…While the LIT-CCSD method has been already benchmarked with the effective interaction hyperspherical harmonic (EIHH) method [11] for the dipole response function [4], here we show a benchmark for the electric dipole polarizability calculated using Eq. (5) with a chiral nucleon-nucleon force derived at next-to-next-to-next-to-next-to-leading order [12].…”