Ragnar Stroberg

Research Interests

My research is focused on ab initio methods for solving the quantum many-body problem for atomic nuclei.

Nuclei are interesting objects in their own right; but a quantitative understanding of nuclei is also essential for understanding extreme astrophysical environments like neutron stars, and for experimental searches for new physics beyond the Standard Model of particle physics.

Ongoing searches for new physics include neutrino-less double beta decay, which would demonstrate lepton-number violation and pin down the mass of the neutrinos; static electric dipole moments of nuclei, which would indicate a violation of time-reversal symmetry and point to the source of the matter-antimatter asymmetry in the universe; searches for signatures of new physics in high-precision measurements of nuclear beta decays; and direct detection of dark matter via WIMP-nucleus scattering. In all these cases, interpretation of the experimental results relies on a nuclear matrix element which cannot be measured experimentally--it must be calculated theoretically with a quantified theoretical error bar.

Such calculations are very challenging because nuclei are quantum mechanical collections tens or hundreds of particles, interacting via a strong and tremendously complicated force. A main effort of my research is in using renormalization group ideas to map a realistic nucleon-nucleon (and 3-nucleon) interaction to an effective valence-space interaction, leveraging the power of the traditional shell model and yielding a tractable many-body problem without the need to fit any parameters. High-performance computing is an essential component of this work.