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Quantum three-body calculation of the nonresonant triple-αreaction rate at low temperatures

The triple-αreaction rate is re-evaluated by directly solving the three-body Schrödinger equation. The resonant and nonresonant processes are treated on the same footing using the continuum-discretized coupled-channels method for three-body scattering. Accurate description of the α-αnonresonant states significantly quenches the Coulomb barrier between the two-α's and the third αparticle. Consequently, the α-αnonresonant continuum states below the resonance at 92.04 keV, i.e., the ground state of 8Be, give markedly larger contribution at low temperatures than in foregoing studies. We show that Nomoto's method for three-body nonresonant capture processes, which is adopted in the NACRE compilation and many other studies, is a crude approximation of the accurate quantum three-body model calculation. We find about 20 orders-of-magnitude enhancement of the triple-αreaction rate around 10^7 K compared to the rate of NACRE.