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

Tuesday October 5, 2021
2:00 pm

 Presenter:  Gordan Krnjaic, Fermilab
 Series:  Nuclear, Particle, Astroparticle and Cosmology (NUPAC) Seminars
 Abstract:  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≈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.
 Host:  Francis-Yan Cyr-Racine
 Location:  Zoom

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