Description du sujet de thèse

This PhD project aims to integrate ab initio nuclear structure methods with ab initio atomic codes to enable high-precision calculations of hyperfine splitting in atoms composed of light nuclei. By bridging nuclear and atomic physics, the research will assess the accuracy of state-of-the-art nuclear Hamiltonians against ultra-precise atomic measurements from the QUARTET collaboration's muonic atom experiments. The PhD candidate will collaborate with experts in Multi-Configuration Dirac-Fock methods to incorporate charge and magnetic density distributions computed from nuclear structure codes. Additionally, the project will develop many-body techniques thattreat bound and continuum states in a unified framework. This approach will refine nuclear Hamiltonians to align with the most precise measurements of light systems, ultimately reducing reliance on empirical fitting.
The PhD student will be based at IJCLab. However, there will be significant exchanges with the team working at TRIUMF (Canada), specifically to collaborate on the advancement of ab initio numerical codes. These codes will permit the computation of both structure and reaction observables within the No-Core Shell Model with Continuum (NCSMC) method. Additionally, significant interactions with the metrology group of the Laboratoire Kastler Brossel, notably Prof. P. Indelicato, at Sorbonne Université (Jussieu campus) in downtown Paris, are planned during the course of the PhD. These interactions will involve feeding Dirac-Fock ab initio codes with nuclear physics inputs, as well as learning the atomistic ingredients and running the code itself to supplement investigations by experimentalists. Eventually, visits to universities hosting experimental colleagues in Germany or Israel can be arranged.
Within the scope of the Joint PhD program, the successful candidate will visit the TRIUMF/UBC campus for two three-week-long visits per year (a total of four visits within the span of the PhD contract). This will contribute to the development of the NCSMC.

Contexte de travail

The predictive accuracy of nuclear models hinges on developing a systematically improvable theoretical framework with precise approximations and robust Uncertainty Quantification (UQ). Effective Field Theories (EFTs), with their capacity to bridge vast scales in nuclear many-body problems, are widely seen as the most promising path forward. However, the reach of ab initio methods remains limited for understanding nuclear structure---how nucleons organize within the nucleus---and for predicting nuclear reactions, which are crucial for advancing our comprehension of astrophysical phenomena.
Nuclear masses and charge radii, along with higher moments of the charge distribution, are well-known, particularly due to precise measurements of the hyperfine splitting of atomic levels. When lasers of the required frequency cannot be engineered, physicists rely on detection systems like muonic atoms, whose hyperfine splitting can be measured with TES microcalorimeters. The extreme precision required in light nuclear systems challenges current nuclear structure methods, which struggle to compute the tail of the nuclear wave function with sufficient accuracy. This limitation affects the sensitive charge distribution and is compounded by inherent inaccuracies in the EFTs used to construct the nuclear Hamiltonian.
This project has two primary goals. First, it aims to fully integrate input from nuclear structure models by accurately computing the charge and magnetic density distributions of light systems with ab initio atomistic codes. These codes can calculate hyperfine splitting, accounting for relativistic and higher-order QED contributions, starting from the nucleus-muonic degrees of freedom while considering nuclear shape and size. Essentially, this requires a consistent treatment of nuclear and atomic physics.
Second, it is essential to develop many-body tools that comprehensively cover the nuclear wave function. This necessitates techniques akin to few-body solvers, where bound and continuum states are treated consistently.
The convergence of these approaches can lead to significant breakthroughs in establishing an accurate EFT or refining its low-energy couplings.
The PhD project aims to achieve these goals. The French team will collaborate with Multi-Configuration Dirac-Fock experts in Paris, using an ab initio atomic code that fully accounts for relativistic effects, essential for elements with Z sup 1. This collaboration will enable direct computation of hyperfine splitting, bridging ab initio approaches from nuclear and atomic physics. The second part of the PhD will explore the implications of the Complex-Scaled Similarity Renormalization Group (CS-SRG) Hamiltonian for the Resonating Group Method basis, investigating whether a Berggren-like basis can facilitate the extraction of accurate optical potentials without explicitly including inelastic channels. This aspect will rely heavily on the NCSMC method, leveraging the consortium's expertise to anticipate significant advances, particularly in studying astrophysically relevant reactions.
The outcomes of this project are relevant to the muonic atom experiments conducted by the QUARTET collaboration\cite{ohayon2024}. Led by French scientists, the collaboration aims to perform muonic atom X-ray measurements at PSI in Switzerland to determine the charge radii of light nuclei with high precision. Both UBC and CNRS groups provide theoretical support for this collaboration.

Le poste se situe dans un secteur relevant de la protection du potentiel scientifique et technique (PPST), et nécessite donc, conformément à la réglementation, que votre arrivée soit autorisée par l'autorité compétente du MESR.

Contraintes et risques

Travel is planned as part of the joint PhD program between CNRS and the University of British Columbia, particularly to work with the theoretical nuclear physics group at the Canadian national laboratory TRIUMF. Travel funding is approximately 3,000 euros per year.

Informations complémentaires

The candidate must hold a master's degree in subatomic physics with a strong emphasis on theoretical aspects. The position requires strong knowledge of theoretical physics, computing/simulation, High Performance Computing (HPC), and mathematics, as well as good oral and written communication skills (French and English required) to present at conferences and write articles for scientific journals. We are looking for a young researcher who will be committed to their project, curious, autonomous, and highly motivated to develop research skills as well as in the required technical areas such as computer modeling/HPC, etc. Additionally, the candidate must be able to work in a team.
Applications must include a detailed CV; at least two references (individuals who may be contacted); a one-page cover letter; a one-page summary of the thesis, as well as the documents necessary to obtain ZRR access (below).
As the position is located in a restricted access area, recruitment is conditional on obtaining a favorable opinion. Consequently, the start date is indicative and may be postponed (documents required: a copy of the passport, a detailed CV, a phone number, the home postal address, the current employer and its address).