Dynamical Lambda models of structure formation

Models of structure formation with a cosmological constant Lambda provide a good fit to the observed power spectrum of galaxy clustering. However, they suffer from several problems. Theoretically, it is difficult to understand why the cosmological constant is so small in Planck units. Observationally, while the power spectra of cold dark matter plus Lambda models have approximately the right shape, the COBE-normalized amplitude for a scale-invariant spectrum is too high, requiring galaxies to be antibiased relative to the mass distribution. Attempts to address the first problem have led to models in which a dynamical field supplies the vacuum energy, which is thereby determined by fundamental physics scales. We explore the implications of such dynamical Lambda models for the formation of large-scale structure. We find that there are dynamical models for which the amplitude of the COPE-normalized spectrum matches the observations. We also calculate the cosmic microwave background anisotropies in these models and show that the angular power spectra are distinguishable from those of standard cosmological constant models.