Osamah Yaghi "Méthode ab-initio de complex scaling pour les systèmes nucléaires légers"

par Osama Yaghi (cnrs)

mardi 22 avr. 2025, 14:00 → 16:00 Europe/Paris

100/-1-A900 - Auditorium Joliot Curie (IJCLab)

Lien de connexion / Link : https://ijclab.zoom.us/j/97430583730?pwd=oq6l1ttzxl4XCgQ6y3ayfGrage0Iqu.1

Merci de laisser fermés camera et micro de votre ordinateur pendant la soutenance.

Please keep your camera and microphone switched off throughout the defense. 

This thesis presents a novel ab-initio method to compute the properties of nuclei in the continuum. The approach combines three well known methods. Namely, the No Core Shell Model (NCSM), Complex Scaling (CS) and Similarity Renormalization Group (SRG). The study addresses numerical challenges and limitations encountered in previous implementations of CS in two-body system and focuses on extending the method to heavier nuclei. To address instabilities in the standard approach of using a complex-scaled harmonic oscillator basis, we introduce an interaction decomposition using polynomial-Gaussian functions, significantly enhancing numerical stability in the two-body system and allowing larger scaling angles. We further investigate the application of SRG to complex-scaled Hamiltonians, modifying the transformation to accommodate complex phases. Additionally, this work provides a detailed investigation of the spectrum of the Hamiltonian in A<=4 systems and introduces analytical tools to facilitate the interpretation and analysis of the results. To benchmark this method, calculations are performed for the A= 4 system, where semi-exact calculations with a finite basis size are feasible. The obtained results agree with exact calculations in the ⁴H and 4n systems. We finish by highlighting areas for further development. This thesis demonstrates the reliability of CS-NCSM for few-body nuclear systems and establishes a foundation for extending the calculations to heavier systems.

 

Abstract.pdf