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arXiv · 2603.27673

Avoiding recollapse in an open-AdS universe via a self-tuning-like mechanism

Yupeng Zhang·Shuxun Tian·Zhengxiang Li
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Abstract

We study whether an open FLRW universe with a negative cosmological constant can evade the eventual recollapse characteristic of an AdS-type universe. Within a power-law realization of Fab-Four theory, we solve the background equations numerically and analyze the asymptotic dynamics. For the representative branch and parameter choice studied here, we find that the scalar sector provides a self-tuning-like compensation for the negative Λ, while the curvature term remains unscreened. As a result, the universe can continue expanding instead of recollapsing. Instead, the universe evolves toward a curvature-dominated linear-expansion regime, a {\propto} t. To probe the underlying compensation mechanism, we further analyze an auxiliary zero-curvature subsystem using Poincaré compactification. In the Λ<0 domain, there exist background trajectories that approach a critical point at infinity. Near this point, the compensating scalar-Λ sector becomes stiff-like, w_{ϕ+Λ} {\to} 1, so that the system effective energy density redshifts faster than curvature (w_k = -1/3). Although this auxiliary analysis does not cover the full curved cosmology, it is consistent with and qualitatively supports the numerical finding that the net ϕ+Λ contribution becomes subdominant to curvature, thereby preventing recollapse despite Λ<0. This extends the application of the self-tuning mechanism to the AdS region and offers a possibility for the AdS Universe predicted by string theory to become a reality.

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Yupeng Zhang, Shuxun Tian, Zhengxiang Li. 2026-07-30. Avoiding recollapse in an open-AdS universe via a self-tuning-like mechanism. https://doi.org/10.1103/d2xt-vpnz

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