arXiv subjects

Hicham Zejli

Publications and source records attributed to Hicham Zejli.

3 recordsLinked to original sources

arXiv2025

Characterization of exotic matter in PT-symmetric wormholes

In our previous work [H. Zejli, Int. J. Mod. Phys. D 34, 2550052 (2025), arXiv:2508.00035], we introduced a PT-symmetric wormhole model based on a bimetric geometry, capable of generating closed timelike curves (CTCs). In this paper, we extend the analysis to the null hypersurface at the throat of this modified Einstein-Rosen bridge, where two regular Eddington-Finkelstein metrics render the geometry traversable. Using the Barrabes--Israel formalism in Poisson's reformulation, we evaluate the null shell's surface stress-energy tensor $S^{αβ}$ from the jump of the transverse curvature, revealing a violation of the null energy condition: a lightlike membrane of exotic matter with negative surface energy density and positive tangential pressure. This exotic fluid acts as a repulsive source stabilizing the throat, ensuring consistency with the Einstein field equations, including conservation laws on the shell. Beyond the local characterization, we outline potential observational signatures: (i) gravitational-wave echoes from the photon-sphere cavity; (ii) horizon-scale imaging with duplicated and through-throat photon rings, and non-Kerr asymmetries; (iii) quantum effects such as PT-induced frequency pairing with possible QNM doublets and partial suppression of vacuum flux at the throat; and (iv) a relic cosmological population yielding an effective $Λ_{\mathrm{eff}}$ and seeding voids. Compared with timelike thin-shell constructions, our approach is based on a null junction interpreted as a lightlike membrane, combined with PT symmetry, providing a distinct route to traversability and clarifying the conditions under which CTCs can arise in a self-consistent framework.

gr-qc↗

arXiv2025

Closed timelike curves in PT-symmetric wormholes

We investigate a modified Einstein-Rosen wormhole model, made unidirectionally traversable through a bimetric geometry defined by two regular metrics, g(+) and g(-), and characterized by PT symmetry combining time reversal (t -> -t) and spatial inversion (x -> -x). In this framework, two distinct spacetime regions are identified at the wormhole throat (r = alpha) via PT symmetry, forming a single spacetime sheet. This model employs Eddington-Finkelstein coordinates to eliminate coordinate singularities at the throat, enabling traversability with a lightlike membrane of exotic matter at the junction to satisfy the Einstein field equations, similar to other traversable wormhole models. We extend this model by coupling two such wormholes to generate closed timelike curves (CTCs), made possible by the opposing causal orientations defined by the two metrics, while adhering to Novikov's self-consistency principle. An effective theory is developed for a scalar field crossing the wormhole, yielding PT-symmetric Klein-Gordon equations with a real energy spectrum ensured by pseudo-unitarity, consistent with quantum mechanical dynamics. These results open new avenues for exploring the effects of PT symmetry on causality and the quantization of scalar fields in traversable geometries.

physics.gen-ph↗

arXiv2024

PT-symmetry in one-way wormholes

In a recent paper, we studied a modified version of the Einstein-Rosen bridge. This modified bridge is traversable and works as a one-way membrane: a particle on the first sheet falling toward the throat will reach it in finite time (in Eddington coordinates), and will continue its trajectory on the second sheet. In this paper, we show that the particle undergoes a PT-symmetry as it crosses the throat. This could lead to observable effects thanks to an additional ingredient proposed by Einstein and Rosen: congruent points on the two sheets are identified. We propose a bimetric model to realize this identification for our modified bridge.

gr-qc↗