2002/09/13 by Maqbool Ahmed, Scott Dodelson, Patrick B. Greene +2 · 119 citations
Mathematics · Physics and Astronomy · #Ansatz #Astrophysics #Black Holes and Theoretical Physics #Computer science #Constant (computer programming) #Cosmological constant #Cosmological constant problem #Cosmology #Cosmology and Gravitation Theories #Dark energy #Mathematical physics #Mathematics #Metric expansion of space #Physics #Pure mathematics #Relativity and Gravitational Theory #Theoretical physics #Unimodular matrix #Universe #astro-ph #gr-qc #hep-th
paper · pdf · doi:10.1103/physrevd.69.103523
published in Physical review. D. Particles, fields, gravitation, and cosmology/Physical review. D. Particles and fields 69(10) (American Physical Society) · 10 pages, 4 figures, LaTeX
arxiv created 2002/09/13 · openalex publication_date 2004/05/27 · arxiv updated 2009/11/30 · openalex created_date 2020/07/02 · openalex updated_date 2026/08/05
A variety of observations indicate that the Universe is dominated by ``dark energy'' with negative pressure, one possibility for which is a cosmological constant. If the dark energy is a cosmological constant, a fundamental question is, why has it become relevant at so late an epoch, making today the only time in the history of the Universe at which the cosmological constant is of the order of the ambient density. We explore an answer to this question drawing on ideas from unimodular gravity, which entails fluctuations in the cosmological constant, and causal set theory, which predicts a specific magnitude for the fluctuations. The resulting ansatz provides a cosmological ``constant'' which fluctuates about zero, remaining always comparable to the ambient energy density.