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arXiv 2606.23331nucl-thphysics.comp-ph
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从少体密度到散射可观测量及其在轻核中的应用

Scattering Observables from Few-Body Densities and Application in Light Nuclei

University of St. Thomas(圣托马斯大学);The Columbian College of Arts and Sciences of The George Washington University(乔治华盛顿大学哥伦比亚文理学院)

Alexander Long

AI总结:

将过渡密度振幅方法应用于轻核散射,通过核密度与过程核的卷积实现计算加速,并开发了Fortran程序包DensityScattering。

摘要:

Griesshammer等人提出的过渡密度振幅(TDA)方法被应用于计算轻核(氢3、氦3、氦4和锂6)的康普顿散射、阈值中性π介子光生和弹性π介子散射的散射可观测量。在该形式中,振幅分解为一个不可约的少体核(编码探针与活性核子的相互作用)和一个过渡密度振幅(携带核结构信息)。由于密度对每个核和动量转移计算一次,然后与任何过程特定的核卷积,相同的核输入在反应中重复使用,相比于直接评估节省了大量计算。这种分解在公开可用的Fortran套件DensityScattering中实现,该套件是本研究的一部分;研究人员实现新反应只需以规定格式提供相应的核,密度处理、积分、量子数求和和输出的基础设施已提供。TDA使用Reinert、Krebs和Epelbaum在截断450和500 MeV下的半局域动量空间规则化手征势从核波函数构建。对于锂6,无核壳模型波函数在相似性重正化群(SRG)变换下演化;为本研究共同开发的反向变换方案(“SRG-And-Back”)将密度返回到物理动量尺度,从而保持原始手征序。诱导的不确定性通过与精确氦4结果在2%水平上的验证,锂6康普顿散射的收敛研究将残余不确定性限制在6%以下。

英文摘要:

The Transition Density Amplitude (TDA) method of Griesshammer et al. is applied to compute scattering observables for Compton scattering, threshold neutral pion photoproduction, and elastic pion scattering on the light nuclei Hydrogen 3, Helium 3, Helium 4, and Lithium 6. In this formalism the amplitude factorizes into an irreducible few-body kernel, which encodes the interaction of the probe with the active nucleons, and a transition density amplitude, which carries the nuclear structure information. Because the densities are computed once per nucleus and momentum transfer and then convolved with any process-specific kernel, the same nuclear input is reused across reactions, yielding substantial computational savings over direct evaluation. This factorization is realized in the publicly available Fortran suite DensityScattering, developed as part of the present work; a researcher implementing a new reaction need only supply the corresponding kernel in a prescribed format, with infrastructure for density handling, integration, quantum-number summation, and output already provided. The TDAs are constructed from nuclear wave functions using the semilocal momentum-space regularized chiral potential of Reinert, Krebs, and Epelbaum at cutoffs of 450 and 500 MeV. For Lithium 6, no-core shell model wave functions are evolved under a Similarity Renormalization Group (SRG) transformation; a back-transformation scheme ("SRG-And-Back"), co-developed for the present work, returns the densities to the physical momentum scale and thereby preserves the original chiral ordering. The induced uncertainty is validated against exact Helium 4 results at the 2% level, and convergence studies for Lithium 6 Compton scattering bound the residual uncertainty below 6%.

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