Decoupling redshift: The key to conciliate global and local estimates of the Universe expansion rate

¹ Departamento de Física, Universidade do Estado do Rio Grande do Norte - Av. Professor Antônio Campos s/n, 59610-210, Mossoró, RN, Brazil
² Departamento de Física, Universidade Federal Rural do Rio de Janeiro - Rodovia BR 465, km 07, s/n 23890-971, Seropédica, RJ, Brazil
³ Programa de Pós- Graduação Interdisciplinar em Física Aplicada, Instituto de Física, Universidade Federal do Rio de Janeiro - Av. Athos da Silveira Ramos, 149, 21941-972, Rio de Janeiro, RJ, Brazil
⁴ Departamento de Física, Universidade Federal de Juiz de Fora - Rua José Lourenço Kelmer, s/n, 36036-330, Juiz de Fora, MG, Brazil

Received: 15 August 2020
Accepted: 1 March 2021

Abstract

To explain the discrepancy between the local and the global estimates of the Universe expansion rate, H₀, becomes one of the most challenging problems in contemporary cosmology. Underestimated systematic errors as well as new physics beyond the standard ΛCDM model, has been invoked to solve, or at least alleviate, this problem. In this paper we show that we can conciliate the local measurement of the Hubble constant with its global estimate in a very simple way without making any of these assumptions. This is achieved if we deal with the decoupling redshift, , as a free parameter. By noting that the dependence of the cosmic microwave background (CMB) observables on H₀ comes from the decoupling redshift we show that, by incorporating a missing parameter, the electron fraction , to the functional form, local and global estimates of H₀ agree with each other perfectly. The effect of introducing is the same that treat as free parameter which should be fitted along with the model parameters. The CMB data and the local estimates of H₀ are reconciled if , a value higher than the value obtained from the usual calculations.