Beta Decay in Medium-Mass Nuclei with the In-Medium Similarity Renormalization Group

We review the status of ab initio calculations of allowed beta decays (both Fermi and Gamow–Teller), within the framework of the valence-space in-medium similarity renormalization group approach.

Dispersion relation analysis of the radiative corrections to gA in the neutron β-decay

We present the first and complete dispersion relation analysis of the inner radiative corrections to the axial coupling constant gA in the neutron β-decay. Using experimental inputs from the elastic form factors and the spin-dependent structure function g1, we determine the contribution from the γW-box diagram to a precision better than 10−4. Our calculation indicates that the inner radiative corrections to the Fermi and the Gamow-Teller matrix element in the neutron β-decay are almost identical, i.e. the ratio λ = gA/gV is almost unrenormalized. With this result, we predict the bare axial coupling constant to be $$ {\overset{\circ }{g}}_A=-1.2754{(13)}_{\mathrm{exp}}{(2)}_{\mathrm{RC}} $$ g ∘ A = − 1.2754 13 exp 2 RC based on the PDG average λ = −1.2756(13).

Multifarious Roles of Hidden Chiral-Scale Symmetry: “Quenching” gA in Nuclei

I discuss how the axial current coupling constant gA renormalized in scale symmetric chiral EFT defined at a chiral matching scale impacts on the axial current matrix elements on beta decays in nuclei with and without neutrinos. The “quenched” gA observed in nuclear superallowed Gamow–Teller transitions, a long-standing puzzle in nuclear physics, is shown to encode the emergence of chiral-scale symmetry hidden in QCD in the vacuum. This enables one to explore how trace-anomaly-induced scale symmetry breaking enters in the renormalized gA in nuclei applicable to certain non-unique forbidden processes involved in neutrinoless double beta decays. A parallel is made between the roles of chiral-scale symmetry in quenching gA in highly dense medium and in hadron–quark continuity in the EoS of dense matter in massive compact stars. A systematic chiral-scale EFT, presently lacking in nuclear theory and potentially crucial for the future progress, is suggested as a challenge in the field.

Manifestation of hidden symmetries in baryonic matter: From finite nuclei to neutron stars

When hadron-quark continuity is formulated in terms of a topology change at a density higher than twice the nuclear matter density [Formula: see text], the core of massive compact stars can be described in terms of quasiparticles of fractional baryon charges, behaving neither like pure baryons nor like deconfined quarks. Hidden symmetries, both local gauge and pseudo-conformal (or broken scale), emerge and give rise both to the long-standing “effective [Formula: see text]” in nuclear Gamow–Teller (GT) transitions at [Formula: see text] and to the pseudo-conformal sound velocity [Formula: see text] at [Formula: see text]. It is suggested that what has been referred to, since a long time, as “quenched [Formula: see text]” in light nuclei reflects what leads to the dilaton-limit [Formula: see text] at near the (putative) infrared fixed point of scale invariance. These properties are confronted with the recent observations in GT transitions and in astrophysical observations.

Gamow-Teller transitions of neutron-rich N = 82, 81 nuclei by shell-model calculations

β-decay half-lives of neutron-rich nuclei around N = 82 are key data to understand the r-process nucleosynthesis. We performed large-scale shell-model calculations in this region using a newly constructed shell-model Hamiltonian, and successfully described the low-lying spectra and half-lives of neutron-rich N = 82 and N = 81 isotones with Z = 42 − 49 in a unified way. We found that their Gamow-Teller strength distributions have a peak in the low-excitation energies, which significantly contributes to the half-lives. This peak, dominated by ν0g7/2 → π0g9/2 transitions, is enhanced on the proton deficient side because the Pauli-blocking effect caused by occupying the valence proton 0g9/2 orbit is weakened.

A comparison of calculated β-decay half-lives with photonuclear reaction data and other experiments

We try to give a comparison of the calculated Gamow–Teller [Formula: see text]-decay half-lives for [Formula: see text], [Formula: see text] and [Formula: see text] nuclei with the experimental ones obtained from ([Formula: see text],p), ([Formula: see text],n) and (n,[Formula: see text]) reactions, respectively. The calculations are performed within the framework of quasi-particle phonon nuclear model. The nucleon–nucleon interaction potential is included according to Pyatov’s restoration method. The calculated decay half-lives are also compared with available experimental data in the literature.