Effective field theory

Effective Field Theory (EFT) is a powerful framework for describing complex physical systems by focusing only on the relevant degrees of freedom at a given energy scale. In nuclear physics, EFT provides a systematic and model-independent approach to understand the strong interactions that bind protons and neutrons into nuclei.

One of the key advantages of EFT is its ability to separate low-energy phenomena from high-energy details, allowing us to build accurate descriptions without requiring a complete theory of the underlying interactions. Instead, the effects of short-distance physics are captured through a series of interactions organized in a low-energy expansion.

Pionless EFT is the simplest incarnation of this approach, designed for systems where the typical momenta are small compared to the pion mass. In this regime, pions—the lightest mesons—can be "integrated out," and nucleons interact via contact terms with increasing complexity. Pionless EFT has proven remarkably successful in describing low-energy nuclear systems, such as few-body bound states and low-energy scattering processes.

Halo EFT is an extension of these ideas tailored to halo nuclei—exotic nuclear systems characterized by a tightly bound core and one or more weakly bound nucleons that form a diffuse halo. These systems exhibit a clear separation of scales, making them ideal candidates for EFT methods. Halo EFT provides a unified framework to describe a wide range of observables in these weakly bound systems, often with minimal input data.