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| Format: | Preprint |
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2026
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| Online Access: | https://arxiv.org/abs/2601.02426 |
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| _version_ | 1866917185824227328 |
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| author | Li, Cong |
| author_facet | Li, Cong |
| contents | We study collinear factorization in strong electromagnetic backgrounds within SCET for a class of modifications where the photon propagator keeps the vacuum pole structure and $i\varepsilon$ prescription, while the background enters only through a numerator tensor $Δ_{μν}(k)$. We show that the set of Landau pinch surfaces and leading momentum regions is unchanged, so the leading-power (LP) factorized form is preserved. Moreover, the LP cusp kernel depends on the background solely through the longitudinal contraction $n^μ\bar n^νΔ_{μν}(k)$ in the soft region; if it vanishes (or is power suppressed), the LP soft kernel reduces to the vacuum. As an application, for an occupancy-number modification with the physical polarization-sum tensor $g_{Tμν}(k;n)$, transversality implies $n^μ\bar n^νΔ_{μν}=0$, so genuine background sensitivity starts only beyond LP. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2601_02426 |
| institution | arXiv |
| publishDate | 2026 |
| record_format | arxiv |
| spellingShingle | On the Stability of Leading-Power Factorization under Photon Propagator Numerator Modifications Li, Cong High Energy Physics - Phenomenology High Energy Physics - Theory We study collinear factorization in strong electromagnetic backgrounds within SCET for a class of modifications where the photon propagator keeps the vacuum pole structure and $i\varepsilon$ prescription, while the background enters only through a numerator tensor $Δ_{μν}(k)$. We show that the set of Landau pinch surfaces and leading momentum regions is unchanged, so the leading-power (LP) factorized form is preserved. Moreover, the LP cusp kernel depends on the background solely through the longitudinal contraction $n^μ\bar n^νΔ_{μν}(k)$ in the soft region; if it vanishes (or is power suppressed), the LP soft kernel reduces to the vacuum. As an application, for an occupancy-number modification with the physical polarization-sum tensor $g_{Tμν}(k;n)$, transversality implies $n^μ\bar n^νΔ_{μν}=0$, so genuine background sensitivity starts only beyond LP. |
| title | On the Stability of Leading-Power Factorization under Photon Propagator Numerator Modifications |
| topic | High Energy Physics - Phenomenology High Energy Physics - Theory |
| url | https://arxiv.org/abs/2601.02426 |