Towards a Realistic Model of Dark Atoms to Resolve the Hubble Tension – on August 25, 2021 at 10:00 am

It has recently been shown that a subdominant hidden sector of atomic dark
matter in the early universe can resolve the Hubble tension while maintaining
good agreement with most precision cosmological observables. However, such a
solution 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 reheat temperatures in both
sectors arise from the decays of an Affleck-Dine scalar field, whose branching
ratios automatically ensure that the reheat 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 that resolve the
Hubble tension.
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