Hot thermal universe endowed with massive dark vector fields and the
  Hubble tension
  The value of Hubble constant inferred from Planck measurements of
anisotropies in the cosmic microwave background is at $4.4\sigma$ tension with
direct astronomical measurements at low redshifts. Very recently, it has been
conjectured that this discrepancy may be reconciled if a small fraction of the
dark matter is described by three mutually orthogonal vector fields of the same
mass. We study the thermal description of this model and use the
observationally-inferred primordial fractions of baryonic mass in $^4{\rm He}$
to constrain its phase space. We show that while the sterile vector fields may
help to alleviate a little bit the existing tension in the measurements of the
Hubble parameter, they cannot eliminate the discrepancy between low- and
high-redshift observations.
