The inconsistent Hubble constant values derived from cosmic microwave background (CMB) observations and from local distance-ladder measurements may suggest new physics beyond the standard ACDM paradigm. It has been found in earlier studies that, at least phenomenologically, non-standard recombination histories can reduce the ≳ 4δ Hubble tension to ∼ 2δ. Following this path, we vary physical and phenomenological parameters in RECFAST, the standard code to compute ionization history of the universe, to explore possible physics beyond standard recombination. We find that the CMB constraint on the Hubble constant is sensitive to the hydrogen ionization energy and 2s → 1s two-photon decay rate, both of which are atomic constants, and is insensitive to other details of recombination. Thus, the Hubble tension is very robust against perturbations of recombination history, unless exotic physics modifies the atomic constants during the recombination epoch.

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非标准重组可以解决哈勃张力吗？

从宇宙微波背景（CMB）观测值和局部距离阶梯测量值得出的不一致的哈勃常数值，可能暗示了标准ACDM范式之外的新物理学。在较早的研究中发现，至少从现象学上来说，非标准的重组历史可以将≳4δ哈勃张力降低至〜2δ。遵循这条路径，我们改变了RECFAST中的物理和现象学参数，RECFAST是计算宇宙电离历史的标准代码，以探索标准重组以外的可能物理学。我们发现哈勃常数的CMB约束对氢电离能和2 s →1 s敏感双光子衰减率，两者都是原子常数，并且对其他重组细节不敏感。因此，哈勃张力对重组历史的扰动是非常强大的，除非在重组时期外来物理改变了原子常数。