Strong Interactions for Precision Nuclear Physics

Abstract

One of the key challenges in ab initio nuclear theory is to understand the emergence of nuclear structure from quantum chromodynamics. I will address this challenge and focus on the statistical aspects of uncertainty quantification and parameter estimation in chiral effective field theory. It is well-known that quantum chromodynamics (QCD) is non-perturbative in the low-energy region where atomic nuclei exist. This feature prevents us from direct application of perturbation theory. To make progress, two complementary approaches are presently employed; lattice QCD (LQCD) [1] and chiral effective field theory (χ EFT) [2]. The former amounts to numerical evaluation of the QCD path integral on a space-time lattice, while the latter is aimed at exploiting the decoupling principles of the renormalization group (RG) to systematically formulate a potential description of the nuclear interaction rooted in QCD. LQCD is a computationally expensive approach that requires at least exascale resources for a realistic analysis of multinucleon systems, and will most likely not be the most economical choice for analyzing nuclear systems. Nevertheless, in cases where numerically converged results can be obtained, LQCD offers a unique computational laboratory for theoretical studies of QCD in a low-energy setting [3]. The derivation of a nuclear potential in χ EFT proceeds via the construction of an effective Lagrangian consisting of pions, nucleons, sometimes also the Δ isobar, endowed with all possible interactions compatible with the symmetries of low-energy QCD. The details can be found in extensive reviews [4-6]. All short-distance physics, normally associated with quarks and gluons, reside beyond a hard momentum scale Λ b ∼ 1 GeV, that remains unresolved in χ EFT. Such high-momentum dynamics is instead encoded in a set of low-energy constants (LECs) that must be determined from experimental data, or in a future scenario hopefully computed directly from LQCD. χ EFT is the theoretical framework to calculate observables in an expan