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 lambda in the observational range. Entropy and density perturbations can be produced.
Journal of High Energy Physics
- Pub Date:
- June 2000
- High Energy Physics - Theory;
- General Relativity and Quantum Cosmology;
- High Energy Physics - Phenomenology
- 30 pages, 1 figure. v2: minor changes, references added