# Alexis Mercenne

## Assistant Professor of Physics

Ph.D., 2016 - University of Caen Normandy

Louisiana State University

Department of Physics & Astronomy

211-C Nicholson Hall, Tower Dr.

Baton Rouge, LA 70803-4001

225-578-8278-Office

### Research Interests

#### Theoretical Nuclear Physics and Astrophysics

As a theoretical nuclear physicist, I specialize in the low-energy structure of the atomic nucleus, with a particular interest in nuclear reactions and their significance to astrophysics. I focus specifically on elements that are far from the beta stability valley on the nuclear chart, which are characterized by an excess of protons or neutrons and are known as "exotic nuclei" due to their extreme instability and short lifetimes. The study of these systems will not only reveal unique features of the atomic nucleus, but also universal properties of open quantum systems, as well as deepen our understanding of the nuclear force and its origins in quantum chromodynamics. Moreover, these short-lived elements play a crucial role in various nucleosynthesis processes, and accurate determination of certain of their properties is essential for describing a range of astrophysical phenomena. A microscopic treatment of nuclear reactions provides a natural framework for studying these exotic systems, allowing us to probe their fundamental properties and calculate cross sections and reaction rates for astrophysical applications.

My research focuses on developing theoretical approaches to nuclear reactions that unite the structure and reactions of nuclei. This involves creating microscopic approaches that account for the internal correlations of each cluster involved in the reaction process through mass partitioning. The Resonating Group Method (RGM) offers a flexible framework that can be formulated to work with any type of many-body wave function and adapt to various purposes. For instance, to investigate weakly bound and unbound systems, many-body wave functions from Gamow Shell Model (GSM) are employed. This is a variation of the shell model based on a single particle basis that incorporates bound states, resonances, and scattering states within a unified framework, enabling couplings to the continuum. By implementing the GSM within the RGM framework, it has been possible to study nuclear reactions involving exotic nuclei, such as the highly unstable proton rich 15F via the scattering of proton on 14O. An ab initio approach to reaction can be developed using many-body wave functions calculated from the Symmetry-adapted No Core Shell Model. This approach allows for the computation of structure observables in medium-mass nuclei from first principles, taking advantage of a many-body basis that captures collective effects such as deformation. By reformulating RGM within this physically relevant many-body basis, high precision evaluation of reaction observables can be achieved, which is a top priority in the field.

Heavy nuclei can be difficult to study due to their large number of nucleons, barring the study of their properties from first principles. The traditional shell model approach may be effective, but the valence space can quickly become too large to handle. In this situation, the Shell Model Monte Carlo method can be used to study heavy nuclei with large valence spaces. This approach is based on a shell model formulation of the auxiliary field Monte Carlo method, and it allows for the calculation of statistical observables such as level densities and gamma-ray strength functions. This is particularly useful for lanthanides and actinides nuclei, as they are key to research on the astrophysical r-process.

To summarize, my research in nuclear physics involves a variety of interesting and important topics, including the quantum many-body problem, open quantum systems, scattering theory, high-performance computing, and the application of machine learning and quantum computing to theoretical nuclear physics.

### Current and Select Publications

- A. Mercenne, K.D. Launey, T. Dytrych, J.E. Escher, S. Quaglioni, G.H. Sargsyan, D. Langr, J.P. Draayer, “Efficacy of the symmetry-adapted basis for ab initio nucleon-nucleus interactions for light- and intermediate-mass nuclei.” Comp. Phys. Commun. 2022; 280:108476. DOI: 10.1016/j.cpc.2022.108476.
- Launey K, Mercenne A, Dytrych T. Nuclear “Dynamics and Reactions in the Ab Initio Symmetry-Adapted Framework.” Annu. Rev. Nucl. Part. Sci. 2021 September 21; 71(1):253-277. DOI: 10.1146/annurev-nucl-102419-033316 3.
- O. M. Molchanov, K. D. Launey, A. Mercenne, G. H. Sargsyan, T. Dytrych, J. P. Draayer “Machine Learning Approach to Pattern Recognition in Nuclear Dynamics from the Ab Initio Symmetry-adapted No-core Shell Model”, Phys. Rev. C (2022) March 3; 105: 034306. DOI: 10.1103/PhysRevC.105.034306.
- V. Girard-Alcindor, A. Mercenne, et al. “Narrow resonances in the continuum of 15F”, Phys. Rev. C (2022) May 11; 105: L051301. DOI: 10.1103/PhysRevC.105.L051301
- F. De Grancey, A. Mercenne, et al. “An above-barrier narrow resonance in 15F”, Phys. Lett. B (2016) July 10; 758: 26. DOI: 10.1016/j.physletb.2016.04.051
- A. Mercenne, N. Michel, M. Ploszajczak “Gamow shell model description of 4He(d,d) elastic scattering reactions”, Phys. Rev. C (2019) April 17; 99: 044606. DOI: 10.1103/PhysRevC.99.044606