Nuclear Axial Currents from Scale-Chiral Effective Field Theory

TL;DR

This paper uses scale-chiral effective field theory to explain why the axial current's space component remains unaffected by density changes, while the time component is enhanced, resolving the long-standing quenched g_A puzzle.

Contribution

It introduces a novel theoretical framework combining hidden symmetries and soft-pion theorems to explain axial current behavior in nuclei, supported by recent ab initio calculations.

Findings

The space component of the axial current remains unaffected by density changes.

The time component of the axial current is strongly enhanced in dense nuclear matter.

Provides a simple resolution to the quenched g_A problem in nuclear beta decays.

Abstract

By incorporating hidden scale symmetry and hidden local symmetry in nuclear effective field theory, combined with double soft-pion theorem, we predict that the Gamow-Teller operator coming from the space component of the axial current should remain unaffected by the QCD vacuum change caused by baryonic density whereas the first forbidden beta transition operator coming from the time component should be strongly enhanced. While the latter has been confirmed since some time, the former is given a support by a powerful recent {\it ab initio} quantum Monte Carlo calculation in light nuclei, also confirming the old "chiral filter hypothesis." Formulated in terms of Fermi-liquid fixed point structure of strong-coupled nuclear interactions, we offer an extremely simple resolution to the long-standing puzzle of "quenched $g_A$", $g_A^{\rm eff}\approx 1$~\cite{quenched}, in nuclear Gamow-Teller beta transitions, giant Gamow-Teller resonances and double beta decays.