Recent experimental and theoretical advancements have led to significant progress in our understanding of the electromagnetic structure of nucleons (), nucleon excitations (), and other baryons. These breakthroughs have been made possible by the capabilities of modern facilities, enabling the induction of photo- and electro-excitation of nucleon resonances. These experiments have specifically probed the evolution of their electromagnetic structure across a range of squared momentum transfer scales, from up to or . These experimental advances have sparked notable developments in theoretical approaches. New theoretical methods have been tested and proven to be robust, marking the beginning of a new era in our understanding on baryons. This includes the study of newly discovered exotic hadrons with various multiquark components. We present a comprehensive review of progress in experimental data on reactions. Additionally, we discuss various analyses and theoretical results, such as quark models in combination (or not) with meson cloud excitations of the baryon quark cores, lattice QCD, Dyson–Schwinger equations, chiral effective field theory, the large limit, and AdS/CFT correspondence, among others. Some of these methods have matured in their predictive power, offering new perspectives on exotic hadrons with multiquark components. We place special emphasis on both the low- and large- regions to reinforce crucial physical constraints on observables that hold in these limits. Furthermore, we illustrate that the combination of lattice QCD with chiral effective field theory and quark models, respectively, proves beneficial in interpreting data and applying constraints within those different regimes. As a practical contribution and for future reference, we review the formulas for helicity amplitudes, multipole form factors and the relations between these two sets of functions for transitions to resonances with general spin . These formulas are ubiquitous and play a pivotal role in experimental and theoretical studies on baryon structure. Notably, the multipole transition form factors for resonances momentum serve as valuable tools to test perturbative QCD results in the large- region, thanks to the correlations between electric and magnetic transition form factors.

中文翻译：

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重子共振的电磁跃迁形状因子

最近的实验和理论进展使我们对核子 ()、核子激发 () 和其他重子的电磁结构的理解取得了重大进展。这些突破是通过现代设施的能力实现的，能够诱导核子共振的光激发和电激发。这些实验专门探讨了其电磁结构在一系列平方动量传递尺度（从 到 或 ）上的演变。这些实验进展引发了理论方法的显着发展。新的理论方法已经过测试并被证明是可靠的，标志着我们对重子的理解进入了一个新时代。这包括对新发现的具有各种多夸克成分的奇异强子的研究。我们对反应实验数据的进展进行了全面的回顾。此外，我们还讨论了各种分析和理论结果，例如与重子夸克核心的介子云激发相结合（或不结合）的夸克模型、晶格 QCD、戴森-施温格方程、手性有效场理论、大极限和 AdS/ CFT 通信等。其中一些方法的预测能力已经成熟，为具有多夸克成分的奇异强子提供了新的视角。我们特别强调低区域和大区域，以加强对保持在这些限制内的可观测量的关键物理约束。此外，我们还说明，晶格 QCD 分别与手性有效场理论和夸克模型相结合，证明有利于解释数据并在这些不同的范围内应用约束。作为实际贡献和供将来参考，我们回顾了螺旋振幅、多极形状因子的公式以及这两组函数之间的关系，用于过渡到一般自旋共振。这些公式无处不在，在重子结构的实验和理论研究中发挥着关键作用。值得注意的是，由于电和磁转变形状因子之间的相关性，共振动量的多极转变形状因子可以作为测试大区域中微扰 QCD 结果的宝贵工具。