Abstract
We examine big bang nucleosynthesis (BBN) in models with a time-varying gravitational constant , when this time variation is rapid on the scale of the expansion rate , i.e, . Such models can arise naturally in the context of scalar-tensor theories of gravity and result in additional terms in the Friedman equation. We examine two representative models: a step-function evolution for and a rapidly oscillating . In the former case, the additional terms in the Friedman equation tend to cancel the effects of an initial value of that differs from the present-day value. In the case of deuterium, this effect is large enough to reverse the sign of the change in (D/H) for a given change in the initial value of . For rapidly oscillating , the effect on the Friedman equation is similar to that of adding a vacuum energy density, and BBN allows upper limits to be placed on the product of the oscillation frequency and amplitude. The possibility that a rapidly oscillating could mimic a cosmological constant is briefly discussed.
- Received 13 December 2023
- Accepted 22 April 2024
DOI:https://doi.org/10.1103/PhysRevD.109.103521
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