Testing $\Lambda$CDM cosmology in a binned universe: anomalies in the deceleration parameter

Understand

We study the reconstructed deceleration parameter splitting the data in different redshift bins, fitting both a cosmographic luminosity distance and also assuming a flat $\Lambda$CDM model, using the Pantheon+ sample of type Ia supernova data (SNIA).

• We observe tensions $\sim 2\sigma-3\sigma$ for different redshift and distance indicators if the full sample is used.
• However, those tensions disappear when the SNIA at $z<0.008$ are removed.
• If the data is splitted in 2 hemispheres according to our movement w.r.t CMB, a strange $3.8 \sigma$ tension appears in one of the samples between particular redshift bins.