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UBC Theses and Dissertations

Electromagnetic properties of medium-mass nuclei from coupled-cluster theory Miorelli, Mirko


Electromagnetic probes represent a fundamental tool to study nuclear structure and dynamics. The perturbative nature of the electromagnetic interaction allows for a clean connection between calculated nuclear structure properties and measured cross sections. Ab initio methods have long represented the gold standard for calculations of nuclear structure observables in light nuclei. Thanks to recent developments in the scientific community, ab initio calculations have finally reached the medium- and heavy-mass region of the nuclear chart. However, the challenges modern nuclear structure calculations face are multiple, ranging from the construction of nuclear forces from chiral effective field theory (χEFT) and the solution of the highly correlated quantum many-body problem, to a quantitative description of observables with solid treatment of uncertainties. The work presented in this thesis aims to contribute addressing some of these challenges, using the ab initio coupled-cluster (CC) theory formulation of the Lorentz integral transform (LIT) method. We combine the CC and LIT methods for the computation of electromagnetic inelastic reactions into the continuum. We show that the bound-state-like equation characterizing the LIT method can be reformulated based on extensions of the coupled-cluster equation-of-motion (EOM) method, and we discuss strategies for viable numerical solutions. We then focus on the calculation of the electric dipole polarizability (α_D), which quantifies the low-energy behaviour of the dipole strength and is related to critical observables such as the radii of the proton and neutron distributions. Using a variety of chiral interactions, and singles and doubles excitations, we study ⁴He, ¹⁶ ²²O and ⁴⁰ ⁴⁸Ca. Exploiting correlations between α_D and the charge radius, we predict the neutron-skin radius and the polarizability for the double-magic ⁴⁸Ca, the latter recently measured by the Osaka-Darmstadt collaboration. Finally, we study the impact of triples excitations on the dipole strength in ⁴He and ¹⁶O.

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