Quantization of four-form fluxes and dynamical neutralization of the cosmological constant

Abstract

A four-form gauge flux makes a variable contribution to the cosmological\nconstant. This has often been assumed to take continuous values, but we argue\nthat it has a generalized Dirac quantization condition. For a single flux the\nsteps are much larger than the observational limit, but we show that with\nmultiple fluxes the allowed values can form a sufficiently dense `discretuum'.\nMultiple fluxes generally arise in M theory compactifications on manifolds with\nnon-trivial three-cycles. In theories with large extra dimensions a few\nfour-forms suffice; otherwise of order 100 are needed. Starting from generic\ninitial conditions, the repeated nucleation of membranes dynamically generates\nregions with a cosmological constant in the observational range. Entropy and\ndensity perturbations can be produced.\n