Dark Energy in the w−cs2 Plane
Abstract
We introduce a unified framework for dark energy diagnostics based on the joint phase space of the equation of state w and the sound speed cs2. The resulting w−cs2 plane provides a minimal extension beyond background cosmology, capturing both the expansion history and perturbative properties within a single representation. Building on this framework, we define the microphysical flow parameter F=dcs2/dw, which encodes the dynamical relation between background evolution and perturbative response. We derive a direct connection between the present-day value F0, H0, and σ8, and show that the microphysical flow parameter enables a hierarchy of increasingly stringent consistency tests that substantially reduce the viable dark energy theory space. We further demonstrate how trajectories in the w−cs2 plane distinguish models that are nearly degenerate at the level of w(a), including canonical quintessence, Chaplygin gas models, and noncanonical scalar field realizations. This framework provides a compact phenomenological bridge between dark energy microphysics and future perturbation-sensitive observations, establishing F0 as a useful discriminator of the kinetic structure underlying cosmic acceleration.
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BibTeX
@misc{trivedi2026dark,
title = {{Dark Energy in the $w-c_s^2$ Plane}},
author = {Oem Trivedi and Robert J. Scherrer and Alfredo Gurrola},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2608.17208},
eprint = {2608.17208},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2608.17208},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Dark Energy in the w−c_s^2 Plane
AU - Oem Trivedi
AU - Robert J. Scherrer
AU - Alfredo Gurrola
PY - 2026
DA - 2026/09/01
PB - arXiv
DO - 10.48550/arxiv.2608.17208
UR - https://arxiv.org/abs/2608.17208
AB - We introduce a unified framework for dark energy diagnostics based on the joint phase space of the equation of state w and the sound speed c_s^2. The resulting w−c_s^2 plane provides a minimal extension beyond background cosmology, capturing both the expansion history and perturbative properties within a single representation. Building on this framework, we define the microphysical flow parameter F=dc_s^2/dw, which encodes the dynamical relation between background evolution and perturbative response. We derive a direct connection between the present-day value F_0, H_0, and σ_8, and show that the microphysical flow parameter enables a hierarchy of increasingly stringent consistency tests that substantially reduce the viable dark energy theory space. We further demonstrate how trajectories in the w−c_s^2 plane distinguish models that are nearly degenerate at the level of w(a), including canonical quintessence, Chaplygin gas models, and noncanonical scalar field realizations. This framework provides a compact phenomenological bridge between dark energy microphysics and future perturbation-sensitive observations, establishing F_0 as a useful discriminator of the kinetic structure underlying cosmic acceleration.
ER -