A hint of matter underdensity at low $z$?
  The $\Lambda$CDM cosmological model provides to first approximation a good
description of the universe, but various tensions with data, most notably
Hubble tension, persist. In this work we confront $\Lambda$CDM with the
Pantheon Type Ia supernovae dataset and perform a two-parameter fit of the
distance modulus for a running cut-off $z_{\textrm{max}}$. We observe that in a
window between $z_{\textrm{max}} \approx 0.1$ and $z_{\textrm{max}} \approx
0.16$ there is a 1 - 2 $\sigma$ discrepancy with the Planck value $\omega_m =
0.315 \pm 0.007$, which points to a potential matter underdensity. For
high-energy theorists, the analysis appears to support the de Sitter Swampland
conjecture.
