About the NTG and Nuclear Physics Theory

The Nuclear Theory Group (NTG) studies a broad range of problems involving the strong interaction.

This research includes the direct study of quantum chromodynamics (QCD), the relativistic field theory of quarks and gluons, as it impacts the structure of protons and of dense matter in neutron stars, as well as the connection of QCD to effective theories of the strong interaction at low energies.

The challenge for nuclear theorists is to develop reliable calculational tools for QCD in the strong interaction regime inside protons and neutron stars, to discover and exploit connections with successful nuclear phenomenology and with nuclear experiments, and to derive systematic descriptions of QCD in terms of low-energy degrees of freedom (hadrons).

Research in the Nuclear Physics Theory Group is progressing in each of these areas. 

EFT and RG Methods

Effective field theory (EFT) and renormalization group (RG) methods have been developed by group members to quantitatively explain how low-energy nuclear phenomenology emerges from QCD. These methods enable systematic and model independent calculations with error estimates from Bayesian statistics, using control over the degrees of freedom to optimize convergence. Group members are among the leaders in applying EFT and RG to nuclear few- and many-body systems and are pioneering applications of QIS and ML technology.

Electroweak Scattering

Electron scattering is an important probe of nuclei. Insight into the crossover from quark-gluon to hadronic descriptions, which is a major goal of the Jefferson Lab experimental program, is possible only if the model dependence of the theoretical descriptions is under control. Light nuclei like helium or deuteron can also serve as laboratories to study the properties of the neutron, as free neutron targets are not available. Toward this end, group members analyze and interpret JLab experiments in the GeV regime with controlled relativistic calculations, and use RG-evolved operators to analyze high-momentum-transfer processes. The description of the final state interaction reaction mechanism for electron scattering can be applied to neutrino scattering, with appropriate changes in the current operator. This is useful for planning and analyzing current and future neutrino experiments. 

Proton Structure

The group works on understanding the inner structure of the proton, a bound state of quarks and gluons. Topis include parton saturation, a new phenomenon predicted to be seen in the proton (and nuclear) wave functions, where the gluons carrying the smallest fractions of the proton momentum merge with each other at the same rate as they split, creating a dense gluonic system. The evidence for saturation is being/will be searched for at present and future high energy hadronic and nuclear, including the Electron-Ion Collider (EIC), to be built at Brookhaven National Laboratory by the early 2030s. The proton spin puzzle has attracted much of the group’s attention as well. The puzzle requires us to find the answer to the following question: “How is the spin (1/2) of the proton distributed among its constituents (quarks and gluons)?" It is an essential problem for our understanding of the proton's inner structure. The group collaborates with physicists at the Jefferson Laboratory in their work on the spin puzzle. 

Dense Matter

The group is also interested in the behavior of strongly interacting matter at high densities and exploring this region of the phase diagram of quantum chromodynamics (QCD), the theory of the strong nuclear force. Group members study the equation of state of matter within neutron stars, the dense remnants of dead stars held from gravitational collapse by repulsive nuclear forces. Specifically, they synthesize inputs from astrophysics, nuclear theory, and particle theory to bound its behavior within the cores of the most massive neutron stars, with the aim of constraining the phase of matter reached in the cores of these objects. This research is interdisciplinary and consists of analytic calculations using perturbative QCD itself as well as numerical and statistical techniques to perform Bayesian equation-of-state inference. Group members also explore transport properties of cold and dense matter, which are more sensitive to the degrees of freedom than thermodynamic properties.

About NTG Members

Among the nuclear theory group faculty are a Hess-Prize recipient and Distinguished University Scholar, an APS Feshbach Prize winner, a DOE Outstanding Junior Investigator and Sackler Prize winner, and several APS and AAAS Fellows.

In addition, the group typically includes several postdoctoral research associates and three to six graduate students.

The group is committed to building a supportive and vibrant research community.

Support for students and postdocs comes from the National Science Foundation (NSF) and the Department of Energy (DOE).

Our group is funded by the NSF and DOE, and the theorists are leading members of funded national networks