Non-degenerate and degenerate wormholes: a unified approach

A generalized notion of degenerate wormholes is introduced, defined by the vanishing of the metric determinant g on the throat and described by the polynomial, g 2 -regularized Einstein field equations. Building on this framework, we show that both the Einstein–Rosen bridge and the Klinkhamer defect wormhole are exact vacuum solutions of the regularized equations, valid globally including at the degenerate throat, while the Klinkhamer configuration additionally admits traversable geometries with b > 2M. In contrast, standard Morris–Thorne and thin-shell wormholes, governed by the conventional (non-regularized) Einstein equations, are intrinsically non-degenerate and necessarily supported by exotic stress–energy. Within a unified regularized system with matter, both thin-shell and Klinkhamer wormholes appear as two qualitatively distinct classes of states—non-degenerate with exotic matter versus degenerate with vacuum—sharing the Einstein–Rosen bridge as a common limiting configuration. This unified viewpoint clarifies why classical null-energy-condition no-go theorems apply only to the non-degenerate sector and suggests the possibility of stationary degenerate traversable wormholes that do not require NEC violation.