摘要: 基于协变密度泛函（CDF）理论，核物质四阶对称能可以被分解为动能部分，同位旋单态势能部分以及同位旋三重态势能部分。交换项的引入明显改变了同位旋单态势能部分和同位旋三重态势能部分的密度行为，特别是来自同位旋标量介子-核子耦合道的交换项贡献提供了一个压制作用。作为一种有益的尝试，引入广义的对称能，可以更直观地统一描述核物质各阶对称能效应。


The density dependence of nuclear fourth-order symmetry energy S₄ is studied within the covariant density functional (CDF) theory in terms of the kinetic energy, isospin-singlet, and isospin-triplet potential energy parts of the energy density functional. When the Fock diagram is introduced, it is found that both isospin-singlet and isospin-triplet components of the potential energy plays important roles in determining the fourth-order symmetry energy. Especially, an extra suppression, which comes from the Fock terms via isoscalar meson-nucleon coupling channels, is revealed in the isospin-triplet potential part of the fourth-order symmetry energy. As an useful attempt, the generalized symmetry energy is introduced to describe the various orders of nuclear symmetry energies in a visual and self-consistent way.