We study theoretically the low-energy electric-dipole response of N=20
isotones. We present results from a quasiparticle random-phase approximation
(QRPA) and a continuum random-phase approximation (CRPA), and we compare them
with results for the mirror Z=20 nuclei. According to our analysis, enhanced E1
strength is expected energetically well below the giant dipole resonance in the
proton-rich isotones. Large amounts of E1 strength in the asymmetric N=20
isotones are predicted, unlike their equally asymmetric Z=20 mirror nuclei,
pointing unambiguously to the role of structural effects such as loose binding.
A proton-skin oscillation could develop especially in 46Fe. The proper
description of non localized threshold transitions and the nucleon effective
mass in mean-field treatments may affect theoretical predictions. We call for
systematic theoretical investigations to quantify the role bulk-matter
properties, in anticipation of measurements of E1 transitions in proton-rich
nuclei.Comment: 10 pages, incl. 9 figures and 2 tables; v2: some rephrasing and
clarifications, corrected Fig.
