{"paper":{"title":"Dark Energy in the $w-c_s^2$ Plane","arxiv_id":"2608.17208","primary_cat":"astro-ph.CO","submitted_at":"2026-08-17T23:44:59+00:00","version_compiled":"v2"},"notice":"Every quoted sentence is the authors' text from the arXiv listing abstract. Labels and probabilities are the outputs of classifier-1.13.0 on the question bank abstract-p1-20260923, exactly as returned. No sentence in this record was written by a language model.","schema":"pith.compiled-record/v0","status":"compiled","abstract":{"source":"arXiv listing abstract v2","sentences":[{"i":0,"p":0.98,"id":"s0","own":true,"role":"contribution","text":"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 $c_s^2$.","hedge":{"p":0.99,"label":"asserted"},"own_p":0.94,"main_claim_p":0.08,"quantitative":false,"quantitative_p":0.04,"role_probabilities":{"gap":0.0,"method":0.02,"result":0.0,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.98,"interpretation":0.0}},{"i":1,"p":0.62,"id":"s1","own":true,"role":"contribution","text":"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.","hedge":{"p":1.0,"label":"asserted"},"own_p":0.8,"main_claim_p":0.09,"quantitative":false,"quantitative_p":0.18,"role_probabilities":{"gap":0.0,"method":0.09,"result":0.01,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.62,"interpretation":0.28}},{"i":2,"p":0.79,"id":"s2","own":true,"role":"contribution","text":"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.","hedge":{"p":1.0,"label":"asserted"},"own_p":0.93,"main_claim_p":0.08,"quantitative":false,"quantitative_p":0.06,"role_probabilities":{"gap":0.0,"method":0.21,"result":0.0,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.79,"interpretation":0.0}},{"i":3,"p":0.86,"id":"s3","own":true,"role":"result","text":"We derive a direct connection between the present-day value $F_0$, $H_0$, and $\\sigma_8$, and show that the microphysical flow parameter enables a hierarchy of increasingly stringent consistency tests that substantially reduce the viable dark energy theory space.","hedge":{"p":1.0,"label":"asserted"},"own_p":0.95,"main_claim_p":0.6,"quantitative":false,"quantitative_p":0.19,"role_probabilities":{"gap":0.0,"method":0.0,"result":0.86,"background":0.0,"limitation":0.0,"future_work":0.0,"contribution":0.12,"interpretation":0.02}},{"i":4,"p":0.66,"id":"s4","own":true,"role":"result","text":"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 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