How and How Much is ${g_A}$ {\it Fundamentally} Quenched in Nuclei?

TL;DR

This paper discusses evidence for significant fundamental quenching of the axial-current coupling constant $g_A$ in nuclei, potentially due to QCD trace anomaly effects, with implications for nuclear interactions and double beta decay processes.

Contribution

It proposes a novel perspective on the origin of $g_A$ quenching, linking it to QCD trace anomaly effects and hidden scale symmetry in nuclear medium.

Findings

Evidence suggests up to 40% quenching of $g_A$ in nuclei.

The quenching may be caused by QCD trace anomaly effects.

Implications for nuclear interactions and double beta decay are discussed.

Abstract

The superallowed Gamow-Teller transition in the doubly-magic-shell nucleus $^{100}$Sn and the high resolution spectral shape analysis in the fourth-forbidden nonunique transition in $^{115}$In indicate as much as $\sim 40\%$ {\it fundamental} quenching in the axial-current coupling constant $g_A$ in nuclei. This can be attributed to an effect of the trace anomaly in QCD "emerging" in nuclear medium. If confirmed, this would signal a major revamping to do in nuclear interactions consistent with chiral-scale symmetry in nuclear medium and a big impact on $0\nu$ and $\nu\nu$ double $\beta$ decays for BSM. I present an argument that such a big anomaly-induced quenching is incompatible with how hidden scale symmetry manifests in nuclear medium, A possible means to resolve this issue is discussed in terms of hidden scale symmetry permeating in baryonic matter from normal nuclear matter to massive compact-star matter.