On generalized theories of varying fine structure constant

Abstract

ABSTRACT We work with a class of scalar extended theory of gravity that can drive the present cosmic acceleration as well as accommodate a mild cosmic variation of the fine structure constant α. The motivation comes from a vintage theory developed by Bekenstein, Sandvik, Barrow, and Magueijo. The α variation is introduced by a real scalar field interacting with charged matter. We execute a cosmological reconstruction based on a parametrization of the present matter density of the Universe. Observational consistency is ensured by comparing the theoretical estimates with JLA + OHD + BAO data sets, using a Markov chain Monte Carlo simulation. An analysis of molecular absorption lines from HIRES and UVES spectrographs is considered as a reference for the variation of α at different redshifts. Two examples are discussed. The first explores a field-dependent kinetic coupling of the scalar field interacting with charged matter. The second example is a generalized Brans–Dicke formalism where the varying α is fitted as an effective matter field. This generates a simultaneous variation of the Newtonian constant G and α. The pattern of this variation may have a crucial role in cosmic expansion history.