利用有效场论寻找晕核中的Efimov现象
摘要
<sec><p indent="0mm">Halo nuclei are a class of exotic nuclear structures that appear near the nuclear drip lines, characterized by a tightly bound core and weakly bound valence nucleons. These nuclei exhibit unique properties due to the low separation energy of the valence nucleons compared to the core’s excitation energy, resulting in a significantly larger spatial distribution than the core itself. Effective field theory (EFT) provides a robust framework for studying these systems by constructing low-energy Lagrangians that treat the core and valence nucleons as degrees of freedom, capturing the long-range physics of halo nuclei. </sec><sec> The halo structure occurs because the valence nucleons tunnel through the potential barrier into classically forbidden regions, forming weakly bound or resonant states near the threshold. The simplest example of such a structure is the deuteron, which can be considered a one-neutron halo nucleus with a proton core. Similar two-body halo structures are found in nuclei such as <sup>19</sup>C and <sup>11</sup>Be (one-neutron halos) and <sup>17</sup>F and <sup>22</sup>Al (one-proton halos). In contrast, two-neutron or two-proton halo nuclei exhibit three-body dynamics. Some of them form Borromean systems where the entire system is bound, but any two-body subsystem is unbound. </sec><sec> EFT, based on the principle of scale separation, constructs Lagrangians at low energy scales, leveraging the large difference between short-range and long-range scales in halo nuclei. This allows the simplification of the core’s internal structure into a point particle model, focusing on the low-energy degrees of freedom. The halo EFT introduces independent fields for the valence nucleons and the core, constructing effective interactions through a power series expansion based on the ratio between scales of the halo and the core. The parameters, known as low-energy constants (LECs), implicitly incorporate the short-range physics, allowing for syst