Abstract
We investigate observational constraints on a specific one-parameter extension to the minimal quintessence model, where the quintessence field acquires a quadratic coupling to the scalar curvature through a coupling constant xi . The value of xi is highly suppressed in typical tracker models if the late-time cosmic acceleration is driven at some field values near the Planck scale. We test xi in a second class of models in which the field value today becomes a free model parameter. We use the combined data from type-Ia supernovae, cosmic microwave background, baryon acoustic oscillations and matter power spectrum, to weak lensing measurements and find a best-fit value xi {>}0.289 where xi = 0 is excluded outside the 95% confidence region. The effective gravitational constant G_mathrm{eff} subject to the hint of a non-zero xi is constrained to -0.003< 1- G_mathrm{eff}/G < 0.033 at the same confidence level on cosmological scales, and it can be narrowed down to 1- G_mathrm{eff}/G < 2.2 times 10^{-5} when combining with Solar System tests.
Highlights
Quintessence with sufficiently flat potentials exhibits attractor solutions such that wide ranges of initial conditions approach the scalar field dominated universe ( φ = 1)
We have considered one of the simplest extensions to the CDM model based on a quintessence field with a nonminimal coupling ξ to gravity
We have in particular focused on the class of models with very weak restrictions on the today’s field value φ0 so that both ξ and φ0 can be treated as free model parameters
Summary
Constraints on the value of ω have been widely studied from the CMB anisotropy and structure formations [36,37,38,39,40], the parametrized post-Newtonian parameters [41,42,43,44], and the big-bang nucleosynthesis [45,46,47] These constraints in terms put a tight bound on the non-minimal coupling as |ξ | < 10−2 in the inverse power-law model of the [14] type, given that the scalar field must reach a Planck scale (φ0 ∼ 1019 GeV) after rolling on the track from arbitrary initial conditions [22].
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