Nuclear Many-Body Theory
These are ultracompact objects the study of which requires an understanding of many areas of physics. A neutron star can be thought of as a laboratory of macroscopic dimensions, containing nucleon matter under extreme conditions. Neutron stars exhibit properties not easily probed in terrestrial laboratories. Their structure is layered, with increasing theoretical uncertainty as one approaches the center of the star. I focus on the crust and core, using terrestrial experiments (see below) to constrain nuclear theory, while also trying to quantify the theoretical uncertainty of astrophysically relevant microscopic calculations.
The interaction between nucleons arises from the fundamental theory of Quantum Chromodynamics. Regardless of their origins, nuclear forces are quite complicated: they depend on much more than the distance between the particles, while they also appear in three- and many- nucleon varieties. Nuclei are the finite systems emerging from these complicated interactions. The current frontier, experimentally attacked in facilities such as TRIUMF (Canada), FAIR (Germany), and FRIB (USA), relates to neutron-rich nuclei. Such studies are closely connected to the physics of neutron-star crusts mentioned above, as these forefront nuclei contain a large fraction of neutrons. I am interested both in the phenomenology of pairing in heavy nuclei and in microscopic approaches to nuclei.
For most of the 20th century the study of pairing using atoms was mainly focused on the fermionic and bosonic varieties of Helium. Then, experimentalists learned how to manipulate alkali gases (bosons in the 1990s, fermions in the 2000s). These systems are especially clean (no unwanted impurities) and can be directly probed. Thus, they can help both toward finding new states of matter and in the effort to simulate the complicated systems appearing in nuclear and condensed-matter physics. Numerous laboratories around the world use cold atoms (such as Li and K) to probe strongly interacting physics. I am interested in the overlap of such atomic systems with the physics of nuclei and neutron stars (e.g. population and mass imbalanced mixtures).
Quantum Monte Carlo
Microscopic simulations offer unprecedented access to strongly interacting systems. Though physical intuition can (and should) be built at weak coupling, the final answer in many cases requires addressing the full problem head on. Among other methods, I use Diffusion Monte Carlo (DMC), Auxiliary-Field Diffusion Monte Carlo (AFDMC), and Path Integral Monte Carlo (PIMC) to calculate ground-state and thermodynamic properties of interacting nucleons or atoms. These simulations tackle a few dozen up to a thousand particles and thus need to be performed on machines ranging from a department cluster to a modern supercomputer.