Orateur
Description
Understanding how atomic nuclei respond to electromagnetic perturbations provides key insights into their structure and dynamics.
In this talk, I will address nuclear response functions, focusing on the electric dipole (E1) mode, one of the most fundamental collective excitations in nuclei. Particular attention will be paid to the Pygmy Dipole Resonance (PDR), an exotic low-energy mode appearing in neutron-rich nuclei. I will present how these excitations can be theoretically described within the Configuration Interaction Shell Model (CI-SM) framework. First, systematically computed E1 strength distributions for all long-lived nuclei in the p- and sd-shell regions will be discussed, compared to predictions from other models and to available photoabsorption data [1,2,3]. The impact of those predictions on the propagation of ultra-high-energy cosmic rays will be presented. Then I will focus on the structure and evolution of the PDR along the Neon and Oxygen isotopic chains, its degree of collectivity, the classical interpretation as a neutron-skin oscillation mode and the isospin-mixed character [1,4].
[1] O. Le Noan and K. Sieja, “Electric dipole response of sd-shell nuclei within the Configuration-Interaction Shell Model approach,” Physical Review C 111, 064308 (2025).
[2] R. W. Fearick, O. Le Noan, H. Matsubara, P. von Neumann-Cosel, K. Sieja, and A. Tamii, “Electric dipole strength in sd-shell nuclei from small-angle proton scattering.” Submitted.
[3] O. Le Noan, S. Goriely, E. Khan, and K. Sieja, Modeling ultra-high-energy cosmic rays propagation using the input from configuration interaction shell model, arXiv:2512.16329 submitted.
[4] O. Le Noan and K. Sieja, ‘’Nature of the pygmy dipole resonance: the Configuration-Interaction Shell-Model point of view. ’’ In Preparation.