Is there evidence for a hotter Universe?
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Regular Article - Theoretical Physics
Is there evidence for a hotter Universe? Carlos A. P. Bengaly1,a , Javier E. Gonzalez2,b , Jailson S. Alcaniz1,2,3,c 1
Observatório Nacional, Rio de Janeiro, RJ 20921-400, Brazil Departamento de Física, Universidade Federal do Rio Grande do Norte, Natal, RN 59072-970, Brazil 3 Instituto Nacional de Pesquisas Espaciais/CRN, Natal, RN 59076-740, Brazil
2
Received: 13 August 2020 / Accepted: 4 October 2020 © The Author(s) 2020
Abstract The measurement of present-day temperature of the Cosmic Microwave Background (CMB), T0 = 2.72548± 0.00057 K (1σ ), 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, H0 , obtained from measurements of the CMB temperature fluctuations assuming the standard ΛCDM model exhibit a large (4.1σ ) tension when compared with low-redshift, model-independent observations. Recently, some authors argued that a slightly change in T0 could alleviate or solve the H0 -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 ≥ 1.9σ from the T0 values required to solve the H0 tension. This result reinforces the idea that a solution of the H0 -tension problem in fact requires either a better understanding of the systematic errors on the H0 measurements or new physics.
1 Introduction About 3 decades ago, the frequency spectrum of the Cosmic Microwave Background (CMB) radiation was measured by the Far-InfraRed Absolute Spectrophotometer (FIRAS) [1]. Over a large range of frequencies, the spectrum obtained was an almost perfect blackbody at a temperature T0 2.73 K, which is the best blackbody spectrum ever measured. Later on, the FIRAS data were recalibrated using the Wilkinson Microwave Anisotropy Probe observations, resulting in one a e-mail:
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c e-mail:
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of the most precise measurements in Cosmology [2] (henceforth F09) T0 = (2.72548 ± 0.00057) K (1σ ).
(1)
More recently, measurements of the temperature fluctuations of the 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 (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 also confirmed the description of the universe provided by the ΛCDM model. In spite of the r
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