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On-shell reduction of spin-zero Duffin–Kemmer–Petiau covariants and implications for the relativistic impulse approximation

Year: 2026
Type: article
Abstract: We analyze the on-shell content of the local Lorentz covariants of the five-dimensional spin-zero Duffin–Kemmer–Petiau algebra in elastic spin-zero–spin-1/2 scattering. The scalar, vector, and tensor structures are reduced explicitly to the two independent amplitudes allowed by the physical parity-conserving process. The two scalar structures are proportional on shell, the genuine nonminimal vector i [ P, β μ ] is longitudinal and vanishes after contraction with the conserved fermion vector current, and the projected vectors Pβ μ and β μ P each reduce to one half of the minimal-vector contribution. The tensor covariants introduce no additional on-shell directions. We discuss the consequences for the four invariant choices used in meson–nucleus optical-potential calculations and show that different nuclear equations can arise only after on-shell-equivalent representatives are promoted to optical operators and iterated beyond the order at which the elementary impulse approximation is fixed. These results provide a systematic basis for distinguishing genuinely independent elementary amplitudes from representation-dependent effects generated by the optical embedding.
DOI: 10.1016/j.physletb.2026.141112
Language: English
Open Access status: diamond
OpenAlex ID: W7224131563
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