Abstract
We study a rapidly oscillating scalar field with potential nonminimally coupled to the Ricci scalar via a term of the form in the action. In the weak coupling limit, we calculate the effect of the nonminimal coupling on the time-averaged equation of state parameter . The change in is always negative for and always positive for (which includes the case where the oscillating scalar field could serve as dark energy), while it can be either positive or negative for intermediate values of . Constraints on the time variation of force this change to be infinitesimally small at the present time whenever the scalar field dominates the expansion, but constraints in the early universe are not as stringent. The rapid oscillation induced in also produces an additional contribution to the Friedman equation that behaves like an effective energy density with a stiff equation of state, but we show that, under reasonable assumptions, this effective energy density is always smaller than the density of the scalar field itself.
- Received 10 October 2017
DOI:https://doi.org/10.1103/PhysRevD.97.023530
© 2018 American Physical Society