Threshold-Aligned Pygmy Dipole Strength in Astrophysical $(n,γ)$ and $(γ,n)$ Reactions
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arXiv
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| Natura: | Preprint |
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2026
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| _version_ | 1866908884180926464 |
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| author | Ghosh, T. Kaur, A. Paar, N. |
| author_facet | Ghosh, T. Kaur, A. Paar, N. |
| contents | Reaction-rate calculations relevant to r-process nucleosynthesis depend sensitively on the nuclear $γ$-strength function ($γ$SF). Here we investigate the impact of low-lying pygmy dipole strength (PDS) in $(n,γ)$ and $(γ,n)$ reactions using $γ$SF based on relativistic nuclear energy density functional theory and propagate these strengths into Hauser--Feshbach statistical model calculations of the reaction rates. We show that considerable reaction-rate enhancements at temperatures relevant for r-process nucleosynthesis are governed by the alignment of the pygmy dipole strength energy with the neutron separation threshold $S_n$ rather than by the total low-energy strength. Consequently, nuclei such as $^{68}$Ni and $^{132}$Sn, where the PDS energy-$S_n$ alignment occurs, exhibit the strongest effects on reaction-rate enhancements. These results demonstrate that modeling reliable reaction rates in r-process nucleosynthesis necessitates accurate microscopic descriptions of low-energy dipole strength, in close synergy with experimental investigations in the vicinity of neutron threshold. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2603_12928 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | Threshold-Aligned Pygmy Dipole Strength in Astrophysical $(n,γ)$ and $(γ,n)$ Reactions Ghosh, T. Kaur, A. Paar, N. Nuclear Theory Reaction-rate calculations relevant to r-process nucleosynthesis depend sensitively on the nuclear $γ$-strength function ($γ$SF). Here we investigate the impact of low-lying pygmy dipole strength (PDS) in $(n,γ)$ and $(γ,n)$ reactions using $γ$SF based on relativistic nuclear energy density functional theory and propagate these strengths into Hauser--Feshbach statistical model calculations of the reaction rates. We show that considerable reaction-rate enhancements at temperatures relevant for r-process nucleosynthesis are governed by the alignment of the pygmy dipole strength energy with the neutron separation threshold $S_n$ rather than by the total low-energy strength. Consequently, nuclei such as $^{68}$Ni and $^{132}$Sn, where the PDS energy-$S_n$ alignment occurs, exhibit the strongest effects on reaction-rate enhancements. These results demonstrate that modeling reliable reaction rates in r-process nucleosynthesis necessitates accurate microscopic descriptions of low-energy dipole strength, in close synergy with experimental investigations in the vicinity of neutron threshold. |
| title | Threshold-Aligned Pygmy Dipole Strength in Astrophysical $(n,γ)$ and $(γ,n)$ Reactions |
| topic | Nuclear Theory |
| url | https://arxiv.org/abs/2603.12928 |