The tower of effective field theories in nuclear physics

Publication in “Reviews of Modern Physics”


Among the fundamental forces of nature, the so-called “strong interaction” plays a crucial role for the existence of matter in the universe. Just how exactly this force, fundamentally described by the theory of quantum chromodynamics as the interaction between quarks and gluons -- elementary particles that cannot be observed in isolation -- brings about the nuclear force that binds protons and neutrons to atomic nuclei is still a matter of active research. Researchers around Professor Hans-Werner Hammer at the Institute of Nuclear Physics have published an article on this topic in the renowned scientific journal Reviews of Modern Physics.

Prof. Dr. Hans-Werner Hammer

The sheer strength of the strong interaction presents a computational challenge, but effective field theories offer a way around this problem. Simply put, such theories boil down microscopic details to their essential content by tailoring the mathematical formalism to the level of detail one aims to describe. This approach can be interpreted as choosing an appropriate "theoretical resolution”, much like stadium screens that are watched only from a large distance can have much larger pixels than a smartphone to ensure the same visual impression.

Following this strategy, the nuclear-physics landscape has been redesigned as a tower of effective field theories formulated in terms of protons and neutrons (or even clusters thereof). These theories emerge from the standard model of elementary particle physics through symmetries and large-scale numerical simulations that run on the world's largest computers. The effective field theories in this sequence are expansions around different low-energy limits of quantum chromodynamics, each with its own characteristics and ranges of applicability. Such theories are a focus of the research in the Collaborative Research Centre 1245 “Nuclei: From Fundamental Interactions to Structure and Stars” at TU Darmstadt.

Artistic representation of the decreasing resolution of the interaction of nuclear particles in the tower of effective field theories.

The paper “Nuclear effective field theory: Status and perspectives” published in ”Reviews of Modern Physics” reviews the different layers of effective field theories used in the description of nuclei and their reactions as well as in broader applications, covering both their history and recent developments.