Is there evidence for a hotter Universe?

Carlos A P Bengaly,Jailson S Alcaniz,Javier E Gonzalez

doi:10.1140/epjc/s10052-020-08522-6

Abstract

The measurement of present-day temperature of the Cosmic Microwave Background (CMB), T_0 = 2.72548 pm 0.00057 K (1sigma ), made by the Far-InfraRed Absolute Spectrophotometer (FIRAS) as recalibrated by the Wilkinson Microwave Anisotropy Probe (WMAP), is one of the most precise measurements ever made in Cosmology. On the other hand, estimates of the Hubble Constant, H_0, obtained from measurements of the CMB temperature fluctuations assuming the standard varLambda CDM model exhibit a large (4.1sigma ) tension when compared with low-redshift, model-independent observations. Recently, some authors argued that a slightly change in T_0 could alleviate or solve the H_0-tension problem. Here, we investigate evidence for a hotter or colder universe by performing an independent analysis from currently available temperature-redshift T(z) measurements. Our analysis (parametric and non-parametric) shows a good agreement with the FIRAS measurement and a discrepancy of ge 1.9sigma from the T_0 values required to solve the H_0 tension. This result reinforces the idea that a solution of the H_0-tension problem in fact requires either a better understanding of the systematic errors on the H_0 measurements or new physics.

Highlights

T0 = (2.72548 ± 0.00057) K (1σ ). (1)More recently, measurements of the temperature fluctuations of the Cosmic Microwave Background (CMB) across the sky have been used to provide stringent constraints on the other cosmological parameters, such as the Hubble constant [3]H0 = (67.36 ± 0.54) km s−1 Mpc−1 (1σ ), (2)a value that was obtained assuming a flat Λ-Cold Dark Matter (ΛCDM) model from the 2018 data release of the Planck Collaboration
A value that was obtained assuming a flat Λ-Cold Dark Matter (ΛCDM) model from the 2018 data release of the Planck Collaboration. Other cosmological probes, such as distance measurements from Type Ia Supernovae [4] and the baryonic acoustic oscillation (BAO) signal from galaxy clustering observations [5] have confirmed the description of the universe provided by the ΛCDM model
In spite of the remarkable concordance among the estimates and measurements of the standard model parameters from different probes, the Planck estimate of the Hubble Constant exhibits a 4.1σ tension with measurements of the current expansion rate from low-redshift standard candles, which were obtained in a model independent-way by the SH0ES experiment [6,7], H0 = (73.5 ± 1.4) km s−1 Mpc−1 (1σ )

Summary

Introduction

A value that was obtained assuming a flat Λ-Cold Dark Matter (ΛCDM) model from the 2018 data release of the Planck Collaboration (hereafter P18) Other cosmological probes, such as distance measurements from Type Ia Supernovae [4] and the baryonic acoustic oscillation (BAO) signal from galaxy clustering observations [5] have confirmed the description of the universe provided by the ΛCDM model. Such a large tension is not reconciled with extensions of the standard cosmology, even though several theoretical attempts have been proposed In some case, they are not able to satisfactorily explain the H0 tension without creating additional discrepancies with the measurements of other parameters [8] and references therein) Another possible route to explain this tension consists in revising the fundamental prior assumptions in cosmological measurements, as recently done by [9] ( IAL20). T0 was indirectly estimated from Planck observations using gravitational lensing and the inte-

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