Revisiting the quasi-molecular mechanism of recombination
  The quasi-molecular mechanism of recombination, recently suggested by
Kereselidze et al., is a non-standard process where an electron and two
neighboring protons in the early universe directly form an ionized hydrogen
molecule in a highly excited state, which then descends to lower levels or
dissociates. It has been suggested that the increased binding energy due to the
participation of a second proton may lead to an earlier cosmic recombination
that alleviates the Hubble tension. Revisiting the quasi-molecular channel of
recombination in more details, we find that the original work significantly
overestimated the probability of finding a pair of adjacent protons in the
relevant epoch ($z\sim $ a few thousand). Our new estimation suggests that the
quasi-molecular mechanism of recombination cannot be the primary cause of the
Hubble tension.
