The Tension of Space as Dark Energy: Dynamics and Phenomenology

We propose a phenomenological framework in which the observed late-time dark-energy sector is interpreted as the intrinsic tension of space itself. Motivated by recent observational hints that the dark-energy equation of state may exhibit mild low-redshift evolution, we begin from an intrinsic membrane description of spacetime and show that a uniform space tension contributes to the gravitational field equations with precisely the tensor structure of vacuum energy. We then consider its Dirac–Born–Infeld completion, which naturally introduces a hidden Abelian $U(1)$ gauge sector on the membrane of space. Within this setting, we study a late-time hidden symmetry-breaking transition $U(1{)}_h\to {\mathbb{Z}}_n$, which reorganizes hidden magnetic energy into a coarse-grained flux-tube reservoir. If this reservoir exchanges energy with the dynamical part of the space-tension sector, the effective dark-energy density becomes time dependent and acquires a nontrivial equation of state. At the background level, the model yields a simple proof-of-concept realization of mild running dark energy and admits a transient crossing of the phantom divide. We compare the resulting evolution with a compressed observational benchmark in the effective Chevallier–Polarski–Linder plane. Although the minimal single-reservoir realization does not exactly reproduce the benchmark target, it generates a phenomenologically relevant low-redshift evolution and points toward a late hidden-sector transition together with a substantial hidden defect population. The construction should therefore be viewed not as a complete theory of dark energy, but as a physically transparent proof of concept.