2000/04/30 by Raphael Bousso, Joseph Polchinski
Physics and Astronomy · #hep-th #astro-ph #gr-qc #hep-ph
paper · pdf · doi:10.1088/1126-6708/2000/06/006
published as JHEP 0006:006,2000 · 30 pages, 1 figure. v2: minor changes, references added
arxiv created 2000/06/26 · arxiv updated 2009/11/30
A four-form gauge flux makes a variable contribution to the cosmological constant. This has often been assumed to take continuous values, but we argue that it has a generalized Dirac quantization condition. For a single flux the steps are much larger than the observational limit, but we show that with multiple fluxes the allowed values can form a sufficiently dense `discretuum'. Multiple fluxes generally arise in M theory compactifications on manifolds with non-trivial three-cycles. In theories with large extra dimensions a few four-forms suffice; otherwise of order 100 are needed. Starting from generic initial conditions, the repeated nucleation of membranes dynamically generates regions with a cosmological constant in the observational range. Entropy and density perturbations can be produced.