Facility for Rare Isotope Beams

At high energy, the fundamental description of matter (Quantum Chromodynamics or QCD) is currently only directly applicable to specific regimes, leaving large portions of the QCD phase diagram uncharted, especially around the regime relevant for neutron stars. To bridge different regimes, the MUSES collaboration has built a cyberinfrastructure that provides descriptions of matter based on first-principle theories and models across the multidimensional QCD phase diagram, including thermodynamics but also observables pertinent to heavy-ion collisions, astrophysics, and more. Our online platform allows users to choose different descriptions (with different parametrizations), how these are connected, and what observables they reproduce. The platform is open for everyone, and all our code is open source.

Committee: Ting Xu (Chairperson), Sergey Baryshev Xianglin Ke, John Lewellen, John Smedley, Remco Zegers

The rapid neutron capture process (r-process) is one of the main mechanisms whereby elements heavier than iron are synthesized, and is entirely responsible for the natural production of the actinides. Now more over 50 years ago, it was proposed that the r-process could occur in the unbinding of material during the inspiral and merger of either a neutron star and black hole, or two neutron stars. Multi-messenger observations of the binary neutron star merger, GW170817, provided the first confirmation of lanthanide production in the merger ejecta. However, the full picture of the role these mergers play in the production of galactic r-process abundances remains unclear. Understanding the intricacies of nucleosynthesis in neutron star mergers is a multi-physics problem spanning several orders of magnitude in both physical and temporal scales. I will discuss work that combines the use of r-process network calculations, general relativistic magnetohydrodynamics simulations with neutrino transport, and chiral effective field theory-informed nuclear equations of state to probe uncertainties in r-process production from post-neutron-star-merger accretion disks.

Despite being discovered over 86 years ago, fission still lacks a complete microscopic description, making it one of the oldest problems in quantum many-body theory. For comparison, superconductivity was discovered in 1911 and described microscopically in 1957 by the BCS theory. Fission is particularly difficult to treat theoretically in a unified manner as it contains many qualitatively distinct processes, each of which occurs at vastly different timescales, from the entrance channel (such as neutron absorption) to the splitting of a deformed nucleus into two fragments to the subsequent emission of radiation (typically gamma rays and neutrons). In 2016, the first simulation of the most rapid and highly non-equilibrium stage of fission, the evolution of the compound nucleus from the outer saddle point to scission to the formation of two fully separated fission fragments (FFs), was achieved for realistic initial conditions. This was done in the framework of the time-dependent superfluid local density approximation (TDSLDA) or equivalently time-dependent density functional theory extended to superfluid systems. Since the first study concerning 240Pu, TDSLDA has been applied extensively to compound systems 236U, 240Pu, and 252Cf (spontaneous fission), and recently to odd systems 239U, 241Pu, and 238Np. During this talk I will summarize the results of such investigations, covering the following topics: the role of pairing correlations during fission, the properties of the FF spins and their correlations, complexity and entanglement, the dynamics of the neck rupture and emission of scission neutrons, the differences between odd and even-even fission dynamics, and the energy dependence of fission observables.

Nuclear ab initio calculations are commonly limited by the computational cost of handling very large tensors, especially when breaking rotational symmetry. Applying a singular value decomposition to nucleon-nucleon and three-nucleon potentials obtained from chiral effective field theory reveals that such interactions possess low-rank structure. Exploiting these low-rank properties could allow to extend the reach of ab initio approaches to heavy open-shell nuclei. However, this is a nontrivial task as it requires reformulation of the computational method used to solve the many-body Schrödinger equation. I will present our ongoing work on employing tensor factorization techniques in Bogoliubov many-body perturbation theory, which uses modern linear algebra algorithms and avoids to construct large many-body tensors in the first place.

TBD

More than 50 years after the discovery of neutrons stars, their interior composition and structure remains unknown. Because the extreme densities and matter asymmetry in neutron star interiors are out of reach for Earth laboratories, the equation of state of bulk nuclear matter is unknown, with important implication for astrophysics and nuclear physics. Thankfully, measurements of neutron stars masses and radii are direct probes of the interior of these compact objects. In the past two decades, X-ray observatories have provided some measurements of neutron star radii and therefore some constraints on the dense matter equation of state. But recently, the results from the NICER Observatory have provided the most promising, robust and precise constraints. I will review some of the key results from the NICER mission (including the most recent measurements) and give an overview of other existing measurements of masses and radii, as well as present their impact on our knowledge of dense nuclear matter. Finally, I will detail future prospects to constrain the equation of state of dense nuclear matter with upcoming X-ray observatories.

The Nuclear Science Summer School (NS3) is a summer school that introduces undergraduate student participants to the fields of nuclear science and nuclear astrophysics. NS3 is hosted by FRIB on the campus of Michigan State University (MSU). The school will offer lectures and activities covering selected nuclear science and astrophysics topics.

PAN introduces participants to the fundamentals of the extremely small domain of atomic nuclei and its connection to the extremely large domain of astrophysics and cosmology.

The PAN @ Michigan State Experience

• Learn about research in one of the top rare-isotope laboratories in the world.
• Get introduced to the fascinating fields of astrophysics, precision measurement, and nuclear science.
• Perform your own nuclear physics experiments.
• Meet researchers who are exploring a wide array of questions.
• Discover the surprising array of career opportunities in science.
• Experience the atmosphere of college life.
• Participants in the 2024 program get free room and board on campus (if required).