On the Cosmological Constant Problems and the Astronomical Evidence for a Homogeneous Energy Density with Negative Pressure

Abstract

In this article the cosmological constant problems, as well as the astronomical evidence for a cosmologically significant homogeneous exotic energy density with negative pressure (quintessence), are reviewed for a broad audience of physicists and mathematicians. After a short history of the cosmological term it is explained why the (effective) cosmological constant is expected to obtain contributions from short-distance physics corresponding to an energy scale at least as large as the Fermi scale. The actual tiny value of the cosmological constant by particle physics standards represents, therefore, one of the deepest mysteries of present-day fundamental physics. In a second part I shall discuss recent astronomical evidence for a cosmologically significant vacuum energy density or an effective equivalent, called quintessence. Cosmological models, which attempt to avoid the disturbing cosmic coincidence problem, are also briefly reviewed.

51 pages, 4 figures, Invited lecture at the first {\it Séminaire Poincaré}, Paris, March 2002

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• Resource Letter: Dark Energy and the Accelerating Universe
• Global Existence of Solutions for the Einstein-Boltzmann System in a Bianchi Type I Space-Time
• Has Dark Energy really been discovered in the Lab?
• Stringy Instability of Topologically Non-Trivial Ads Black Holes and of desitter S-Brane Spacetimes
• Global existence of solutions for the Einstein-Boltzmann system with cosmological constant in the Robertson-Walker space-time for arbitrarily large initial data
• Cosmological Higgs fields
• Einstein-Schrodinger theory in the presence of zero-point fluctuations
• Global existence of solutions to the Einstein-massive scalar field equations with a cosmological constant for a perfect fluid on the flat Robertson-Walker space-time
• Does the cosmological constant stay hidden?