Cosmological variation of the fine structure constant from an ultralight scalar field: The effects of mass

Abstract

Cosmological variation of the fine structure constant a due to the evolution of a spatially homogeneous ultralight scalar field (m;H0) during the matter and L dominated eras is analyzed. Agreement of Da/a with the value suggested by recent observations of quasar absorption lines is obtained by adjusting a single parameter, the coupling of the scalar field to matter. Asymptotically a(t) in this model goes to a constant value a ’a 0 in the early radiation and the late L dominated eras. The coupling of the scalar field to ~nonrelativistic! matter drives a slightly away from a in the epochs when the density of matter is important. Simultaneous agreement with the more restrictive bounds on the variation uDa/au from the Oklo natural fission reactor and from meteorite samples can be achieved if the mass of the scalar field is on the order of 0.5‐0.6HL , where HL5V L H0. Depending on the scalar field mass,a may be slightly smaller or larger than a 0 at the times of big bang nucleosynthesis, the emission of the cosmic microwave background, the formation of early solar system meteorites, and the Oklo reactor. The effects on the evolution of a due to nonzero mass for the scalar field are emphasized. An order of magnitude improvement in the laboratory technique could lead to a detection of (a ˙/a) 0.