2004/10/31 by Wayne Hu · 8 citations
Physics and Astronomy · #Black Holes and Theoretical Physics #Cosmology and Gravitation Theories #Galaxies: Formation, Evolution, Phenomena #astro-ph
paper · pdf · doi:10.1103/physrevd.71.047301
published as Phys.Rev.D71:047301,2005 · 4 pages, 2 figures; changes reflect PRD published version
arxiv created 2005/01/27 · openalex publication_date 2005/02/02 · arxiv updated 2011/05/12 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/28
Dark energy constraints have forced viable alternatives that differ substantially from a cosmological constant \ensuremathΛ to have an equation of state w that evolves across the phantom divide set by \ensuremathΛ. Naively, crossing this divide makes the dark energy gravitationally unstable, a problem that is typically finessed by unphysically ignoring the perturbations. While this procedure does not affect constraints near the favored cosmological constant model it can artificially enhance the confidence with which alternative models are rejected. Similar to the general problem of stability for w<0, the solution lies in the internal degrees of freedom in the dark energy sector. We explicitly show how to construct a two scalar field model that crosses the phantom divide and mimics the single field behavior on either side to substantially better than 1% in all observables. It is representative of models where the internal degrees of freedom keep the dark energy smooth out to the horizon scale independently of the equation of state.