Fundamental physics with ESPRESSO: Constraining a simple parametrisation for varying α

¹ Instituto de Astrofísica e Ciências do Espaço, Faculdade de Ciências da Universidade de Lisboa, Campo Grande, 1749-016 Lisboa, Portugal
e-mail: vitor.dafonseca@alunos.fc.ul.pt
² Departamento de Física da Faculdade de Ciências da Universidade de Lisboa, Edifício C8, 1749-016 Lisboa, Portugal
³ ECEO, Universidade Lusófona de Humanidades e Tecnologias, Campo Grande, 376, 1749-024 Lisboa, Portugal
⁴ INAF – Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34143 Trieste, Italy
⁵ Institute for Fundamental Physics of the Universe, Via Beirut 2, 34151 Miramare, Trieste, Italy
⁶ Instituto de Astrofísica de Canarias (IAC), Calle Vía Láctea s/n, 38205 La Laguna, Tenerife, Spain
⁷ Departamento de Astrofísica, Universidad de La Laguna (ULL), 38206 La Laguna, Tenerife, Spain
⁸ Instituto de Astrofísica e Ciências do Espaço, CAUP, Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
⁹ Centro de Astrofísica da Universidade do Porto, Rua das Estrelas, 4150-762 Porto, Portugal
¹⁰ Faculdade de Ciências e Tecnologia, Universidade Nova de Lisboa, 2829-516 Caparica, Portugal
¹¹ Istituto Nazionale di Fisica Nucleare, Sezione di Trieste, Via Bonomea 265, 34136 Trieste, Italy
¹² Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Victoria 3122, Australia
¹³ Observatoire Astronomique de l’Université de Genève, Chemin Pegasi 51, Sauverny 1290, Switzerland
¹⁴ Departamento de Física e Astronomia, Faculdade de Ciências, Universidade do Porto, Rua Campo Alegre, 4169-007 Porto, Portugal
¹⁵ INAF – Osservatorio Astrofisico di Torino, via Osservatorio 20, 10025 Pino Torinese, Italy
¹⁶ Centro de Astrobiología (CSIC-INTA), Crta. Ajalvir km 4, 28850 Torrejón de Ardoz, Madrid, Spain

Received: 15 April 2022
Accepted: 15 July 2022

Abstract

Context. The spectrograph ESPRESSO recently obtained a limit on the variation of the fine-structure constant, α, through measurements along the line of sight of a bright quasar with a precision of 1.36 ppm at 1σ level. This imposes new constraints on cosmological models with a varying α. We assume such a model where the electromagnetic sector is coupled to a scalar field dark energy responsible for the current acceleration of the Universe. We parametrise the variation of α with two extra parameters, one defining the cosmological evolution of the quintessence component and the other fixing the coupling with the electromagnetic field.

Aims. The objective of this work is to constrain these parameters with both astrophysical and local probes. We also carried out a comparative analysis of how each data probe may constrain our parametrisation.

Methods. We performed a Bayesian analysis by comparing the predictions of the model with observations. The astrophysical datasets are composed of quasar spectra measurements, including the latest ESPRESSO data point, as well as Planck observations of the cosmic microwave background. We combined these with local results from atomic clocks and the MICROSCOPE experiment.

Results. The constraints placed on the quintessence parameter are consistent with a null variation of the field, and are therefore compatible with a ΛCDM cosmology. The constraints on the coupling to the electromagnetic sector are dominated by the Eötvös parameter local bound.

Conclusions. More precise measurements with ESPRESSO will be extremely important to study the cosmological evolution of α as it probes an interval of redshift not accessible to other types of observations. However, for this particular model, current available data favour a null variation of α resulting mostly from the strong MICROSCOPE limits.