Elastic positivity from a modified forward dispersion relation constrains the twelve dim-8 Wilson coefficients of the photon–dark-photon EFT to a spectrahedral cone, with hierarchies for non-forward mixed amplitudes and distinct loci for kinetic-mixing and dark-axion UV completions.
The Positivity Geometry of Photon--Dark-Photon Effective Field Theories
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abstract
We derive positivity bounds on the complete dimension-eight effective field theory of photons and a massless dark photon. The mixed gauge sector contains twelve CP-even Wilson coefficients and an enlarged helicity-amplitude structure. Using a modified forward-limit dispersion relation, we analytically obtain non-trivial linear and non-linear elastic positivity constraints that define a spectrahedral geometry. We analyze implications of these bounds on non-forward amplitudes and discuss where kinetic-mixing and dark-axion-portal UV completions populate this geometry.
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The Positivity Geometry of Photon--Dark-Photon Effective Field Theories
Elastic positivity from a modified forward dispersion relation constrains the twelve dim-8 Wilson coefficients of the photon–dark-photon EFT to a spectrahedral cone, with hierarchies for non-forward mixed amplitudes and distinct loci for kinetic-mixing and dark-axion UV completions.