Revisiting the temperature evolution law of the CMB with gaussian processes

TL;DR

This paper uses Gaussian Process regression to analyze CMB temperature evolution, revealing potential deviations from the standard law at low redshifts and tensions with direct measurements, suggesting possible new physics or variations in fundamental constants.

Contribution

It introduces a novel application of Gaussian Processes to reconstruct CMB temperature evolution from observational data, highlighting potential deviations and tensions with established measurements.

Findings

Potential deviations from the standard temperature-redshift relation at low z

A ~2σ tension with COBE/FIRAS measurements of T_CMB(0)

Implications for variations in fundamental constants like α

Abstract

In this work, we perform a statistical inference of the classical background law governing the evolution of the temperature of the cosmic microwave background radiation (CMB), given by $T_{\rm CMB}(z) = T_0(1 + z)$. To this end, we employ Gaussian Process (GP) regression techniques to reconstruct the temperature evolution based on two observational datasets: (i) CMB-Sunyaev-Zel'dovich (SZ) cluster measurements and (ii) CMB-interstellar medium (ISM) interaction data. Our analysis reveals interesting results that may suggest potential deviations from the standard temperature-redshift relation, particularly at low redshifts ($z < 0.5$), where discrepancies up to $\sim$2$\sigma$ are observed. Additionally, we identify a mild but noteworthy tension, also at the $\sim$2$\sigma$ level, between our GP inferred value of the present-day CMB temperature, $T_{\rm CMB}(z=0)$, and the precise direct measurement from the COBE/FIRAS experiment. We also explore possible phenomenological implications of our findings, including interpretations associated with possible variations in fundamental constants, such as the fine-structure constant $\alpha$, which could provide a physical explanation for the observed deviations at low redshift.