无芯壳模型中$^4$He光吸收截面的有限谱洛伦兹积分变换计算
Finite-spectrum Lorentz integral transform calculation of the $^{4}$He photoabsorption cross section in the no-core shell model
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中文总结 AI 辅助
本研究在从头算无芯壳模型中开发并验证了洛伦兹积分变换的有限谱实现，用于计算$^4$He光吸收截面，其结果与已有数据符合且有新特征，提供了可控的计算路径。
中文摘要 AI 辅助
我们在从头算无芯壳模型（NCSM）中开发并验证了洛伦兹积分变换（LIT）的有限谱实现，用于计算$^4$He的光吸收截面。在NCSM中显式计算了大量$1^-$本征态，并根据它们的激发能和对应的E1跃迁强度构建了LIT。这种有限谱方法是光吸收截面计算中LIT方法的常规非齐次方程和基于兰索斯的实现的补充。使用Daejeon16相互作用，我们提取了光吸收截面，并检验了其对模型空间截断、激发能截断和LIT参数的稳定性。通过将从离散NCSM谱得到的E1极化率和轫致辐射求和规则，与从提取的截面积分得到的相同量进行比较，评估了有限谱提取的可靠性。提取的截面捕捉了$^4$He光子核数据在巨偶极共振区域的主要特征，在低能上升段和主峰区域，与之前基于兰索斯评估的手征相互作用NCSM-LIT结果一致，而采用Daejeon16相互作用的当前计算呈现出更明显的高能肩峰。本工作提供了一条可控的有限谱NCSM-LIT路径，从显式计算的多体本征态和跃迁强度得到光吸收截面。
英文摘要
We develop and validate a finite-spectrum implementation of the Lorentz integral transform (LIT) within the \textit{ab initio} no-core shell model (NCSM) for calculating the photoabsorption cross section of $^4$He. A large set of $1^-$ eigenstates is explicitly calculated in the NCSM, and the LIT is constructed from their excitation energies and the corresponding $E1$ transition strengths. This finite-spectrum approach is complementary to conventional inhomogeneous-equation and Lanczos-based implementations of the LIT method for photoabsorption cross sections. Using the Daejeon16 interaction, we extract the photoabsorption cross section and examine its stability with respect to the model-space truncation, excitation-energy cutoff, and LIT parameters. The reliability of the finite-spectrum extraction is assessed by comparing the $E1$ polarizability and bremsstrahlung sum rule obtained from the discrete NCSM spectrum with the same quantities obtained by integrating the extracted cross section. The extracted cross section captures the principal features of the available $^4$He photonuclear data in the giant-dipole-resonance region and is consistent, in the low-energy rise and main-peak region, with earlier chiral-interaction NCSM-LIT results obtained from Lanczos-based evaluations, while the present calculation with the Daejeon16 interaction exhibits a more pronounced high-energy shoulder. The present work provides a controlled finite-spectrum NCSM-LIT route from explicitly calculated many-body eigenstates and transition strengths to photoabsorption cross sections.
