alpha-alpha Scattering in Halo Effective Field Theory

TL;DR

This paper develops an effective field theory for alpha-alpha interactions, capturing the delicate balance of forces leading to a narrow resonance, and compares its predictions with experimental phase shift data.

Contribution

It introduces a novel power counting scheme that accounts for electromagnetic and strong interactions in alpha-alpha scattering within EFT.

Findings

Accurately describes low-energy alpha-alpha phase shifts

Reveals fine-tuning needed for data fit

Provides insights into conformal invariance in nuclear systems

Abstract

We study the two-alpha-particle (alpha-alpha) system in an Effective Field Theory (EFT) for halo-like systems. We propose a power counting that incorporates the subtle interplay of strong and electromagnetic forces leading to a narrow resonance at an energy of about 0.1 MeV. We investigate the EFT expansion in detail, and compare its results with existing low-energy alpha-alpha phase shifts and previously determined effective-range parameters. Good description of the data is obtained with a surprising amount of fine-tuning. This scenario can be viewed as an expansion around the limit where, when electromagnetic interactions are turned off, the Be-8 ground state is at threshold and exhibits conformal invariance. We also discuss possible extensions to systems with more than two alpha particles.