Transition from three dimensions to one dimension in Bose gases at zero temperature

We investigate the effects of dimensional reduction in Bose gases induced by a strong harmonic confinement in the transverse cylindric radial direction. By using a generalized Lieb-Liniger theory, based on a variational treatment of the transverse width of the Bose gas, we analyze the transition from a three-dimensional Bose-Einstein condensate to the one-dimensional Tonks-Girardeau gas. The sound velocity and the frequency of the lowest compressional mode give a clear signature of the regime involved. We also study the case of negative scattering length deriving the phase diagram of the Bose gas (uniform, single soliton, multisoliton, and collapsed) in toroidal confinement.