Some attempts of easing the critical Hubble tension present in modern cosmology have resorted to using variations of fundamental constants, such as the fine-structure constant, at the time of recombination. In this article we demonstrate that there are critical hurdles to construct such viable models using scalar fields, due to the striking precision of local constraints on the fine-structure constant stability. These hurdles demonstrate that in single-field models one has to extremely fine-tune the shape of the potential and/or the initial conditions. Indeed, for single-field models in a potential that is not fine-tuned we can put a generic bound at recombination of $\mathrm{\Delta }\alpha /\alpha <5\times {10}^{-4}$ (95% CL).

中文翻译：

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重组时精细结构常数变化与局部观察不相容

缓解现代宇宙学中存在的临界哈勃张力的一些尝试已诉诸于在重组时使用基本常数的变化，例如精细结构常数。在本文中，我们证明了使用标量场构建此类可行模型存在关键障碍，因为精细结构常数稳定性的局部约束具有惊人的精度。这些障碍表明，在单场模型中，必须对势的形状和/或初始条件进行极其微调。事实上，对于未微调势的单场模型，我们可以在重组时设置一个通用界限$\mathrm{\Delta }\alpha /\alpha <5\times {10}^{-4}$（95% CL）。