Towards a Realistic Model of Dark Atoms to Resolve the Hubble Tension

Understand

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.