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| Natura: | Preprint |
| Pubblicazione: |
2025
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| Accesso online: | https://arxiv.org/abs/2507.18234 |
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| _version_ | 1866909859800154112 |
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| author | Pascalutsa, Vladimir |
| author_facet | Pascalutsa, Vladimir |
| contents | The Burkhardt--Cottingham sum rule is an exact superconvergence relation for a spin-structure function, derived from general principles of light absorption and scattering, and valid at any momentum transfer $Q^2$. I illustrate how a class of such relations emerges from the Siegert point, an unphysical kinematical point where both the probe and the target are at rest. From light-by-light scattering, new sum rules for $γ^\ast γ^\ast$ fusion are emerging, valid for arbitrary photon virtualities. Regarding the convergence of these relations, there is a simple argument for the suppression of longitudinal photon polarizations at high energy. Among its consequences is the prediction of $σ_L/ σ_T \to 0$ at high energy, for the ratio of unpolarized nucleon photoabsorption cross sections. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2507_18234 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | New superconvergence relations for spin and tensor structure functions of $γγ$ fusion Pascalutsa, Vladimir High Energy Physics - Phenomenology High Energy Physics - Theory Nuclear Theory The Burkhardt--Cottingham sum rule is an exact superconvergence relation for a spin-structure function, derived from general principles of light absorption and scattering, and valid at any momentum transfer $Q^2$. I illustrate how a class of such relations emerges from the Siegert point, an unphysical kinematical point where both the probe and the target are at rest. From light-by-light scattering, new sum rules for $γ^\ast γ^\ast$ fusion are emerging, valid for arbitrary photon virtualities. Regarding the convergence of these relations, there is a simple argument for the suppression of longitudinal photon polarizations at high energy. Among its consequences is the prediction of $σ_L/ σ_T \to 0$ at high energy, for the ratio of unpolarized nucleon photoabsorption cross sections. |
| title | New superconvergence relations for spin and tensor structure functions of $γγ$ fusion |
| topic | High Energy Physics - Phenomenology High Energy Physics - Theory Nuclear Theory |
| url | https://arxiv.org/abs/2507.18234 |