# Effective Field Theory

Effective Field Theories (EFTs) are powerful tools widely used in modern theoretical physics and they enable in nuclear physics the consistent construction of nuclear forces systematically connected to Quantum Chromodynamics (QCD). The central idea of an EFT is to reduce the microscopic details of a given physical system to its essential content, tailoring the mathematical formalism to the level of detail one aims to describe. This can be understood as choosing an appropriate “theoretical resolution.” Much like screens watched from a distance can have larger pixels than a smartphone to ensure the same visual impression for the viewer, the approach is very economic and elegant.

In nuclear physics EFTs tame the immense complexity of QCD at low energies by describing nuclei in terms of hadrons (or even collective degrees of freedom) rather than in terms of quarks and gluons. The figure illustrates this for the tower of nuclear EFTs that involve nucleons, pions, and clusters of nucleons as degrees of freedom. It starts from Chiral EFT with presumably largest range of applicability, moving to Pionless EFT most suited to the low-energy regime where it is not important to explicitly resolve pion exchange, and further to Halo/Cluster EFT, which describes systems where even the substructure of a "core" to which valence nucleons are loosely bound need not be resolved explicitly.

My work addresses open questions in the construction and application of these theories as well as their connections.