Dipole Strength from First Principles Calculations

The electric dipole polarizability quantifies the low-energy behavior of the dipole strength. It is related to the proton and neutron distributions of the nucleus, and thereby can be used to constrain the neutron equation of state and the physics of neutron stars. Only recently however, new developments in ab initio methods finally allowed first principles studies of the dipole strength in medium-mass nuclei [1,2,3]. Using the Lorentz integral transform coupled cluster method with the newly developed chiral interaction at next-to-next-to-leading order (NNLO_sat) we study the low energy behavior of the dipole strength in 4He, 16O, 22O [3] and 48Ca for which the polarizability has been recently measured by the Osaka-Darmstadt collaboration. For the exotic 22O we observe large contribution to the dipole strength at very low energy, indicating the presence of a pygmy dipole resonance, in agreement with what experimentally found by Leistenschneider et al.[4]. [1] S. Bacca, N. Barnea, G. Hagen, G. Orlandini, and T. Papenbrock, Phys. Rev. Lett. 111, 122502 (2013) [2] S. Bacca, N. Barnea, G. Hagen, M. Miorelli, G. Orlandini, and T. Papenbrock, Phys. Rev. C 90, 064619 (2014) [3] M. Miorelli, S. Bacca, N. Barnea, G. Hagen, G. R. Jansen, G. Orlandini, and T. Papenbrock, Phys. Rev. C 94, 034317 (2016) [4] A. Leistenschneider et al., Phys. Rev. Lett. 86, 5442–5445 (2001)"