An internal polarization current in QCD string fragmentation provides a unified explanation of anomalous soft photons

Soft-photon yields in several hadronic reactions exceed conventional inner-bremsstrahlung estimates based on Low’s theorem, whereas leptonic channels and the lowest-energy hadronic measurement agree with QED. We show that a local nonperturbative electromagnetic polarization current generated during QCD string fragmentation is sufficient to account quantitatively for this excess-and-null pattern. The current is carried by fractionally occupied, constrained spacelike internal modes, which we call photonic-complement modes; they remain tied to timelike hadronization sources and do not occur as asymptotic states. Current conservation fixes the lowest-order parity-even transverse current, and its retarded response makes the additional amplitude 𝑂(𝑘), leaving the Low and Burnett–Kroll terms unchanged. Source occupation is described by a positive-semidefinite density matrix. For a complete timelike–spacelike pair, the coherence matrix is the Hadamard product of the two reduced coherence matrices, suppressing collective emission when shower histories become distinguishable. We implement the current in PYTHIA 8/Lund event records. A twoparameter global fit describes seven fixed-target excess and null measurements with 𝜒2 = 10.16 for five degrees of freedom. Fixing the parameters from WA102 and NA22 𝐾+𝑝 and predicting the remaining five reactions gives 𝜒2 = 10.44. A local component, fixed before the fixed-target analysis, reproduces the DELPHI rates, transverse-momentum spectrum, and neutral-to-charged multiplicity dependence within 4.3%, with acceptable ten-bin and sixteen-cell tests. These results establish a unified generator-level explanation of the existing data. The model predicts no additional source in 𝑒+𝑒- → 𝜇+𝜇- and no 5MeV meson-valence component in proton- or lepton-initiated reactions. Both null predictions directly test the proposed source without additional normalization or parameter adjustment.