Towards a Realistic Model of Dark Atoms to Resolve the Hubble Tension
  It has recently been shown that a subdominant hidden sector of atomic dark
matter in the early universe provides a novel avenue towards resolving the
Hubble ($H_0$) tension while maintaining good agreement with Cosmic Microwave
Background era observables. However, such a mechanism requires a hidden sector
whose energy density ratios are the same as in our sector and whose
recombination also takes place at redshift $z \approx 1100$, which presents an
apparent fine tuning. We introduce a realistic model of this scenario that
dynamically enforces these coincidences without fine tuning. In our setup, the
hidden sector contains an identical copy of Standard Model (SM) fields, but has
a smaller Higgs vacuum expectation value (VEV) and a lower temperature. The
baryon asymmetries and reheating temperatures in both sectors arise from the
decays of an Affleck-Dine scalar field, whose branching ratios automatically
ensure that the reheating temperature in each sector is proportional to the
corresponding Higgs VEV. The same setup also naturally ensures that the
Hydrogen binding energy in each sector is proportional to the corresponding
VEV, so the ratios of binding energy to temperature are approximately equal in
the two sectors. Furthermore, our scenario predicts a correlation between the
SM/hidden temperature ratio and the atomic dark matter abundance and
automatically yields values for these quantities favored by concordant early-
and late-universe measurements of $H_0$.
