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Title: Dark energy models in the w-w{sup '} plane

Abstract

We examine the behavior of dark energy models in the plane defined by w (the equation of state parameter for the dark energy) and w{sup '} (the derivative of w with respect to the logarithm of the scale factor). For nonphantom barotropic fluids with positive squared sound speed, we find that w{sup '}<3w(w+1), the opposite of the bound on quintessence models previously derived by Caldwell and Linder. Thus, these barotropic models and quintessence models for the dark energy occupy disjoint regions in the w-w{sup '} plane. We also derive two new bounds for quintessence models in the w-w{sup '} plane: the first is a general bound for any scalar field with a monotonic potential, while the second improves on the Caldwell-Linder bound for tracker quintessence models. Observationally distinguishing barotropic models from quintessence models requires {sigma}(w{sup '}) < or approx. 1+w.

Authors:
 [1]
  1. Department of Physics and Astronomy, Vanderbilt University, Nashville, Tennessee 37235 (United States)
Publication Date:
OSTI Identifier:
20776719
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. D, Particles Fields; Journal Volume: 73; Journal Issue: 4; Other Information: DOI: 10.1103/PhysRevD.73.043502; (c) 2006 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; COSMOLOGY; EQUATIONS OF STATE; FLUID MECHANICS; NONLUMINOUS MATTER; POTENTIALS; SCALAR FIELDS; SOUND WAVES; VELOCITY

Citation Formats

Scherrer, Robert J. Dark energy models in the w-w{sup '} plane. United States: N. p., 2006. Web. doi:10.1103/PhysRevD.73.043502.
Scherrer, Robert J. Dark energy models in the w-w{sup '} plane. United States. doi:10.1103/PhysRevD.73.043502.
Scherrer, Robert J. Wed . "Dark energy models in the w-w{sup '} plane". United States. doi:10.1103/PhysRevD.73.043502.
@article{osti_20776719,
title = {Dark energy models in the w-w{sup '} plane},
author = {Scherrer, Robert J.},
abstractNote = {We examine the behavior of dark energy models in the plane defined by w (the equation of state parameter for the dark energy) and w{sup '} (the derivative of w with respect to the logarithm of the scale factor). For nonphantom barotropic fluids with positive squared sound speed, we find that w{sup '}<3w(w+1), the opposite of the bound on quintessence models previously derived by Caldwell and Linder. Thus, these barotropic models and quintessence models for the dark energy occupy disjoint regions in the w-w{sup '} plane. We also derive two new bounds for quintessence models in the w-w{sup '} plane: the first is a general bound for any scalar field with a monotonic potential, while the second improves on the Caldwell-Linder bound for tracker quintessence models. Observationally distinguishing barotropic models from quintessence models requires {sigma}(w{sup '}) < or approx. 1+w.},
doi = {10.1103/PhysRevD.73.043502},
journal = {Physical Review. D, Particles Fields},
number = 4,
volume = 73,
place = {United States},
year = {Wed Feb 15 00:00:00 EST 2006},
month = {Wed Feb 15 00:00:00 EST 2006}
}
  • Important observables to reveal the nature of dark energy are the equation of state w and its time derivative in units of the Hubble time w{sup '}. Recently, it was shown that the simplest scalar field models of dark energy (quintessence) occupy rather narrow regions in the w-w{sup '} plane. We extend the w-w{sup '} plane to w<-1 and derive bounds on w{sup '} as a function of w for tracker phantom dark energy. We also derive bounds on tracker k-essence. The observational window for w{sup '} for w<-1 is not narrow, {sigma}(w{sup '}) < or approx. 6(1+w)
  • No abstract prepared.
  • The w-w{sup '} plane, defined by the equation of state parameter for the dark energy and its derivative with respect to the logarithm of the scale factor, is useful to the study of classifying the dynamical dark energy models. In this note, we examine the evolving behavior of the two-field quintom models with w crossing the w=-1 barrier in the w-w{sup '} plane. We find that these models can be divided into two categories, type A quintom in which w changes from >-1 to <-1 and type B quintom in which w changes from <-1 to >-1 as the universemore » expands.« less
  • We apply the bulk holographic dark energy in general 5D two-brane models. We extract the Friedmann equation on the physical brane and we show that in the general moving-brane case the effective 4D holographic dark energy behaves as a quintom for a large parameter-space area of a simple solution subclass. We find that w{sub {Lambda}} was larger than -1 in the past while its present value is w{sub {Lambda}{sub 0}} Almost-Equal-To -1.05, and the phantom bound w{sub {Lambda}} = -1 was crossed at z{sub p} Almost-Equal-To 0.41, a result in agreement with observations. Such a behavior arises naturally, without themore » inclusion of special fields or potential terms, but a fine-tuning between the 4D Planck mass and the brane tension has to be imposed.« less
  • Spanning the whole functional space of cosmologies with any admissible DE state equations w(a) seems a need, in view of forthcoming observations, namely those aiming to provide a tomography of cosmic shear. In this paper I show that this duty can be eased and that a suitable use of results for constant-w cosmologies can be sufficient. More in detail, I ''assign'' here six cosmologies, aiming to span the space of state equations w(a) = w{sub o}+w{sub a}(1−a), for w{sub o} and w{sub a} values consistent with WMAP5 and WMAP7 releases and run N-body simulations to work out their non-linear fluctuationmore » spectra at various redshifts z. Such spectra are then compared with those of suitable auxiliary models, characterized by constant w. For each z a different auxiliary model is needed. Spectral discrepancies between the assigned and the auxiliary models, up to k ≅ 2–3 h Mpc{sup −1}, are shown to keep within 1 %. Quite in general, discrepancies are smaller at greater z and exhibit a specific trend across the w{sub o} and w{sub a} plane. Besides of aiming at simplifying the evaluation of spectra for a wide range of models, this paper also outlines a specific danger for future studies of the DE state equation, as models fairly distant on the w{sub 0}-w{sub a} plane can be easily confused.« less