Two-body weak currents in heavy nuclei

TL;DR

This paper investigates the impact of two-body weak currents on Gamow-Teller strength and beta-decay rates in heavy nuclei using energy-density functional theory, revealing complex effects beyond simple quenching models.

Contribution

It introduces a systematic study of two-body axial currents in heavy nuclei within energy-density functional theory, highlighting their nuanced effects on nuclear decay properties.

Findings

Two-body currents generally quench Gamow-Teller strength and decay rates.

Effects of two-body currents decrease with increasing neutron excess.

Low-lying transition rates can be enhanced, especially in neutron-rich nuclei.

Abstract

In light and medium-mass nuclei, two-body weak currents from chiral effective field theory account for a significant portion of the phenomenological quenching of Gamow-Teller transition matrix elements. Here we examine the systematic effects of two-body axial currents on Gamow-Teller strength and $\beta$-decay rates in heavy nuclei within energy-density functional theory. Using a Skyrme functional and the charge-changing finite amplitude method, we add the contributions of two-body currents to the usual one-body linear response in the Gamow-Teller channel, both exactly and though a density-matrix expansion. The two-body currents, as expected, usually quench both summed Gamow-Teller strength and decay rates, but by an amount that decreases as the neutron excess grows. In addition, they can enhance individual low-lying transitions, leading to decay rates that are quite different from those that an energy-independent quenching would produce, particularly in neutron-rich nuclei. We show that both these unexpected effects are related to changes in the total nucleon density as the number of neutrons increases.