Microscopic constitutive theory for extraordinary NED–plasma propagation

Develop a microscopic constitutive model that combines the extraordinary nonlinear-electrodynamic vacuum response with the dielectric response of a material plasma, thereby determining a unique dispersion relation for extraordinary NED perturbations propagating through plasma.

Background

In vacuum, extraordinary perturbations in nonlinear electrodynamics propagate according to an effective optical metric defined only up to conformal transformations, because conformally related metrics have identical null trajectories. A material plasma introduces a dimensionful plasma-frequency term, which is not conformally invariant, so the vacuum characteristic conformal class does not uniquely determine propagation in the presence of plasma.

The paper therefore treats minimally coupled test radiation in an external plasma unambiguously using the background spacetime metric, while presenting the extraordinary NED–plasma continuation only as a phenomenological prescription. A microscopic constitutive theory is left necessary to establish the unique physical dispersion relation and make corresponding observational predictions.

References

Consequently, a unique dispersion relation combining the extraordinary NED cone with a material plasma cannot be inferred from the vacuum effective metric alone; it requires a microscopic constitutive model incorporating both the nonlinear vacuum response and the dielectric response of the medium.

— Two-scale magnetically charged regular black holes from nonlinear electrodynamics and a T-duality-inspired zero-point length  (2608.12541 - Ovgun et al., 12 Aug 2026) in Introduction, discussion of combining nonlinear electrodynamics with a material plasma