Random values of the cosmological constant

One way that an anthropic selection mechanism may be manifest in a physical theory involves multiple domains in the universe with different values of the physical parameters. If this mechanism is to be relevant for understanding the small observed value of the cosmological constant, it may involve a mechanism by which some contributions to the cosmological constant can be fixed at a continuous range of values in the different domains. I study the difficulties of four possible mechanisms. A commonly cited possibility, the Hubble damping of a scalar field with a very flat potential, is seen to require unnatural fine-tuning in the initial conditions. More promising is the possibility of having fixed random values of non-dynamical form fields, and a cosmological mechanism is suggested. Further requirements needed for a consistent cosmology are discussed.