2026/07/27 by Zhiqi Huang
Physics and Astronomy · #astro-ph.CO #gr-qc #hep-ph #hep-th
We combine the axiverse with a negative cosmological constant Λ, both originating from the string landscape, and apply an observation-time-weighted anthropic argument. Adopting a uniform prior on Λ and a typical string-motivated axion decay constant comparable to the reduced Planck scale, this framework predicts a ∼ 40% probability of observing 0.1 < Ωm < 0.9, thereby naturally resolving the long-standing fine-tuning and coincidence problems of dark energy. Unlike many scalar-field dark energy models, the anthropic Lambda-axion universe (ALAverse) statistically disfavors slow-roll dynamics, as slow-roll requires fine-tuning of the initial field displacement. Moreover, the negative cosmological constant renders fast-roll scenarios anthropically unfavorable, since they typically yield only a very brief observational window with positive dark energy density. Having ruled out both extremes, the ALAverse characteristically predicts a moderate-roll dynamics. We derive a two-parameter parametrization in terms of δΩ and |εs| that covers ALAverse solutions as well as a broad class of canonical and phantom field models. Current observational data yield δΩ= -0.0498 ± 0.0186, corresponding to a 2.7σ rejection of ΛCDM (δΩ= 0) and phantom models (δΩ> 0). The data also show a mild preference for the ALAverse over slow-roll quintessence, a trend that can be conclusively tested with future high-precision measurements of the Hubble diagram.