Triple-α reaction rates below T9=3 by a non-adiabatic three-body model
Abstract
The triple-α reaction from the ternary continuum states at off-resonant energies, α+α+α→12C, remains an open question. This direct process is scrutinized using a non-adiabatic Faddeev hyperspherical harmonics R-matrix expansion method, and the derived reaction rates are discussed. After reviewing the model, the resultant photo-disintegration of 12C(2+1→ 0+) is shown to be much smaller than the values predicted by the adiabatic models for 0.15 E 0.35 MeV. Despite the large difference, the derived reaction rates are illustrated to be concordant with the current evaluated rates for 0.08 T9 3. The difference below E=0.20 MeV can be seen in the rates for T9 0.07. In comparison with the calculations, the rates are found to be reduced by a factor of 10-4 at T9=0.05, because of an accurate description for 8Be break-up. Uncertainties of the rates are also estimated by examining the sensitivity to the 3α potentials. By introducing three-body S-factors and a resonant term, the present rates are expressed in an analytic form, and they are provided in a tabular form for astrophysical applications. To update the evaluated rates, non-resonant sequential process between α+8Be could be removed. The astrophysical impact is not expected to be large, although the rates are reduced around T9=0.05.
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