Highly anisotropic Bose-Einstein condensates: Crossover to lower dimensionality

We develop a simple analytical model based on a variational method to explain the properties of trapped cylindrically symmetric Bose-Einstein condensates of varying degrees of anisotropy, well into the regimes of effective one dimension and effective two dimensions. Our results are accurate in regimes where the Thomas-Fermi approximation breaks down and they are shown to be in agreement with recent experimental data. We also present analytic expressions for various ground-state properties and quasiparticle excitations valid for highly anisotropic condensates.