  The current expansion rate of the Universe, the Hubble constant $H_0$, is an
important cosmological quantity. However, two different ways to measure its
value do not agree -- building a low-redshift distance ladder leads to a higher
value of $H_0$ than inferring it from high-redshift observations in a
$\Lambda$CDM cosmology. Most approaches to solve this tension either act at
very low redshift by modifying the local distance ladder, or at high redshift
by introducing new physics that changes the normalization of the inverse
distance ladder. Here we discuss a way to address the Hubble tension at
intermediate redshifts instead. By keeping the low- and high-redshift
normalizations unchanged, we find a violation of the distance duality in the
redshift range where luminosity and angular diameter distances overlap. We
'solve' this problem by introducing a redshift-dependent systematic effect that
brings the luminosity distance into agreement with the angular diameter
distance. The resulting expansion history is no longer compatible with
$\Lambda$CDM, but this can be fixed with a dynamical dark energy component. In
this way, we are able to solve the Hubble tension at intermediate redshifts.

Cosmology and Nongalactic Astrophysics