Can cosmological observations uniquely determine the nature of dark energy ?

Abstract

The observational effect of all minimally coupled scalar field models of dark energy can be determined by the behavior of the following two parameters : (1) equation of state parameter $w$, which relates dark energy pressure to its energy density, and (2) effective speed of sound $c_e^2$, which relates dark energy pressure fluctuation to its density fluctuation. In this paper we show that these two parameters do not uniquely determine the form of a scalar field dark energy Lagrangian even after taking into account the perturbation in the scalar field. We present this result by showing that two different forms of scalar field Lagrangian can lead to the same values for these paired parameters. It is well known that from the background evolution the Lagrangian of the scalar field dark energy cannot be uniquely determined. The two models of dark energy presented in this paper are indistinguishable from the evolution of background as well as from the evolution of perturbations from a FRW metric.

9 pages, 2 figures, few references added

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Cited by in corpus (12)

• Refining inflation using non-canonical scalars
• Primordial black holes and gravitational waves from non-canonical inflation
• A note on perfect scalar fields
• Cosmic acceleration in non-canonical scalar field model - An interacting scenario
• Sound speed of scalar field dark energy: weak effects and large uncertainties
• A short review on clustering dark energy
• A comparison of perturbations in fluid and scalar field models of dark energy
• Dynamics of generalized tachyon field
• Perturbed dark energy: classical scalar field versus tachyon
• A new generic evolution for $k$-essence dark energy with $w\approx -1$
• Tachyonic vs Quintessence dark energy: linear perturbations and CMB data
• Constraints on non-canonical chaotic inflation from ACT DR6 and BICEP/Keck data