The Cosmological Constant and the String Landscape

Abstract

Theories of the cosmological constant fall into two classes, those in which the vacuum energy is fixed by the fundamental theory and those in which it is adjustable in some way. For each class we discuss key challenges. The string theory landscape is an example of an adjustment mechanism. We discuss the status of this idea, and future directions.

35 pages, 2 figures. Rapporteur talk at the 23rd Solvay Conference in Physics, December, 2005. v2: Small changes. Author notes that this is not a review article but a discussion of a few specific issues

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• Effective Actions for Regge Piecewise Flat Quantum Gravity
• Cosmological Constant of the $(p+1)$-Dimensional World, Embedded in the $d$-Dimensional Bulk Space
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• Gravastar-like black hole solutions in $q$-theory
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• String Theory Bounds on the Cosmological Constant, the Higgs mass, and the Quark and Lepton Masses
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• The Universe as a Set of Topological Fluids with Hierarchy and Fine Tuning of Coupling Constants in Terms of Graph Manifolds
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