Testing Acdm Cosmology In A Binned Universe: Anomalies In The Deceleration Parameter

We study the reconstructed deceleration parameter splitting the data in different redshift bins, fitting both a cosmographic luminosity distance and also assuming a flat ΛCDM model, using the Pantheon+ sample of type Ia supernova data (SNIA). We observe tensions ∼2σ−3σ 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 3.8σ tension appears in one of the samples between particular redshift bins. Finally, considering posterior distribution as Gaussian, general linear model prefers a positive slope for q0 across redshift bins opposed to a zero slope expected in a ΛCDM universe. We discuss possible explanations for our results and the influence of lowest redshift SNIA data in cosmological analysis.