Oscillating scalar fields in extended quintessence

Dan Li, Shi Pi, and Robert J. Scherrer
Phys. Rev. D 97, 023530 – Published 25 January 2018

Abstract

We study a rapidly oscillating scalar field with potential V(ϕ)=k|ϕ|n nonminimally coupled to the Ricci scalar R via a term of the form (18πG0ξϕ2)R in the action. In the weak coupling limit, we calculate the effect of the nonminimal coupling on the time-averaged equation of state parameter γ=(p+ρ)/ρ. The change in γ is always negative for n2 and always positive for n<0.71 (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 n. Constraints on the time variation of G 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 G 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

Physics Subject Headings (PhySH)

Gravitation, Cosmology & Astrophysics

Authors & Affiliations

Dan Li1,2, Shi Pi3, and Robert J. Scherrer2

  • 1School of Science, Zhejiang University of Science and Technology (ZUST), 318 LiuHe Road, Hangzhou 310023, China
  • 2Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235, USA
  • 3Center for Gravitational Physics, Yukawa Institute for Theoretical Physics, Kyoto University, Kyoto 606-8502, Japan

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Issue

Vol. 97, Iss. 2 — 15 January 2018

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