Exploring a coupling between dark energy and photons: cosmic dynamics and the variation of α

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2024, Tutor: Adrià Gómez Valent Dynamical dark energy (DE) is an alternative to a positive cosmological constant Λ. In this work we model the DE dynamics by means of a quintessence scalar field, considering a coupling between DE and photons that triggers the cosmological evolution of the fine structure constant α. We derive the coupled system of differential equations that rules the universe expansion at the background level and solve it numerically. We also constrain the model with state-of-the-art cosmological data and obtain strong upper bounds on the parameters that control the DE dynamics and the coupling with the electromagnetic sector. Finally, we compare the fitting results with those obtained from ΛCDM and uncoupled quintessence. As original contribution of our work, we have developed a code that is publicly available in [https://github.com/amunozna/alpha_phi_CDM_coupling.git].