The triple alpha reaction is a key to $^{12}$C production and is expected to occur in weakly-coupled, thermal plasmas as encountered in normal stars. We investigate how Coulomb screening affects the structure of a system of three alpha particles in such a plasma environment by precise three-body calculations within the Debye-Hückel approximation. A three-alpha model that has the Coulomb interaction modified in the Yukawa form is employed. Precise three-body wave functions are obtained by a superposition of correlated Gaussian bases with the aid of the stochastic variational method. The energy shifts of the Hoyle state due to the Coulomb screening are obtained as a function of the Debye screening length. The results, which automatically incorporate the finite size effect of the Hoyle state, are consistent with the conventional result based on the Coulomb correction to the chemical potentials of ions that are regarded as point charges in a weakly-coupled, thermal plasma. We have given a theoretical basis to the conventional point-charge approach to the Coulomb screening problem relevant for nuclear reactions in normal stars by providing the first evaluation of the Coulomb corrections to the $Q$ value of the triple alpha process that produces a finite size Hoyle state.
Time-dependent Hartree-Fock calculations have been performed for fusion reactions of He-4 + He-4 -> Be*-8, followed by He-4 + Be*-8 . Depending on the orientation of the initial state, a linear chain vibrational state or a triangular vibration is found in 12C, with transitions between these states observed. The vibrations of the linear chain state and the triangular state occur at ~9 and 4 MeV respectively.
The triple-alpha process, whereby evolved stars create carbon and oxygen, is believed to be fine-tuned to a high degree. Such fine-tuning is suggested by the unusually strong temperature dependence of the triple-alpha reaction rate at stellar temperatures. This sensitivity is due to the resonant character of the triple-alpha process, which proceeds through the so-called "Hoyle state" of $^{12}$C with spin-parity $0^+$. The question of fine-tuning can be studied within the {\it ab initio} framework of nuclear lattice effective field theory, which makes it possible to relate {\it ad hoc} changes…
The physical principles that determine the effect of the electron shell of an atom on the alpha decay rate of the nucleus are presented. The effect is shown to be negative. Numerical calculations of the effect in helium-like ions are performed. It accounts for more than 80% of the effect in neutral atoms. The prospects for experimental detection of the effect in the storage rings of the GSI Darmstadt, ISF Lanzhou are discussed.
We present an ab initio calculation of the quark mass dependence of the ground state energies of ^4He, ^8Be and ^{12}C, and of the energy of the Hoyle state in ^{12}C. These investigations are performed within the framework of lattice chiral Effective Field Theory. We address the sensitivity of the production rate of carbon and oxygen in red giant stars to the fundamental constants of nature by considering the impact of variations in the light quark masses and the electromagnetic fine-structure constant on the reaction rate of the triple-alpha process. As carbon and oxygen are essential to lif…
The first excited $J^π=0^+$ state of $^{12}$C, the so-called Hoyle state, plays an essential role in a triple-$α$ ($^4$He) reaction, which is a main contributor to the synthesis of $^{12}$C in a burning star. We investigate the Coulomb screening effects on the energy shift of the Hoyle state in a thermal plasma environment using precise three-$α$ model calculations. The Coulomb screening effect between $α$ clusters are taken into account within the Debye-Hückel approximation. To generalize our study, we utilize two standard $α$-cluster models, which treat the Pauli principle between the $α$ pa…
Heavy Quarkonium in a weakly-coupled quark-gluon plasma below the melting temperature
我们计算了一个夸克-胶子等离子体中的重夸克偶素能级和衰变宽度，该等离子体的温度T和屏蔽质量m_D满足m α_s >> T >> m α_s^2>> m_D（m是重夸克质量），m α_s^5阶。我们首先顺序地积分出尺度m、m α_s和T，然后，我们使用区域积分技术在所得到的有效理论中进行计算。确定了一个共线区域，该区域以该顺序起作用。我们还讨论了我们的结果对重离子碰撞中重夸克偶素抑制的影响。
