Observational signatures of dark energy produced in an ancestor vacuum: Forecast for galaxy surveys

TL;DR

This paper explores a model where dark energy arises from quantum fluctuations in an ancestor vacuum, predicting a distinctive evolution of the equation of state and potential observational signatures in galaxy surveys.

Contribution

It introduces a novel dark energy model based on bubble nucleation and quantum fluctuations, linking dark energy to residual effects from an ancestor vacuum and analyzing its observational implications.

Findings

Dark energy's equation of state approaches -1 in the future.

Dark energy effectively increases the magnitude of negative spatial curvature.

Galaxy surveys alone have limited constraints due to parameter degeneracy.

Abstract

We study observational consequences of the model for dark energy proposed in [1] (Aoki et al., Phys.Rev. D97 (2018) no.4, 043517). We assume our universe has been created by bubble nucleation, and consider quantum fluctuations of an ultralight scalar field. Residual effects of fluctuations generated in an ancestor vacuum (de Sitter space in which the bubble was formed) is interpreted as dark energy. Its equation of state parameter w(z) has a characteristic form, approaching -1 in the future, but -1/3 in the past. A novel feature of our model is that dark energy effectively increases the magnitude of the negative spatial curvature in the evolution of the Hubble parameter, though it does not alter the definition of the angular diameter distance. We perform Fisher analysis and forecast the constraints for our model from future galaxy surveys by Square Kilometre Array and Euclid. Due to degeneracy between dark energy and the spatial curvature, galaxy surveys alone can determine these parameters only for optimistic choices of their values, but combination with other independent observations, such as CMB, will greatly improve the chance of determining them.