Nuclear Physics
Nuclear physics tries to describe systems interacting dominantly through interactions that are a consequence of Quantum Chromodynamics (QCD). QCD is the theoretical framework that describes the interactions between quarks and gluons in the standard model, however, it is also responsible for the interactions between neutrons and protons is responsible for the binding of these into nuclei. Nucleons can be considered as the relevant degrees of freedom in nuclei as they are tightly bound. As a consequence, a theory built around nucleons is a good starting point for the description of nuclei. Since the nucleon-nucleon system displays furthermore various widely separated scales, effective field theory is an approach that has gained momentum in this field in the recent past.
Ultracold Atoms
The field of ultracold atoms is very broad. I am interested in strongly interacting systems of ultracold atoms and how the microscopic interactions between the atoms lead to novel phenomena. During the last years, I have focused mostly on systems that display a large scattering length. The system becomes strongly interacting when the scattering length becomes large. Specifically, in systems composed out of bosons, microscopic few-body processes will have a major impact on their stability.
The Approach: Effective Field Theory
Effective field theory (EFT) is a universal approach to systems that display a separation of scales. The EFT is then formulated in terms of the minimal number of degrees of freedom as a systematic low-energy expansion. A separation of scales exists, for example, in the weak interaction that is mediated by vector mesons whose mass is larger than the typical momentum scale involved in weak decays. One can therefore use the scale separation between momentum and mass to construct a low-energy expansion in powers of q/M. The first order of this effective field theory is a pointlike interaction that corresponds to Fermi's theory of the weak interaction.