Bright-like soliton solution in quasi-one-dimensional BEC in third order   on interaction radius
  Nonlinear Schr\"{o}dinger equations and corresponding quantum hydrodynamic (QHD) equations are widely used in studying ultracold boson-fermion mixtures and superconductors. In this article, we show that a more exact account of interaction in Bose-Einstein condensate (BEC), in comparison with the Gross-Pitaevskii (GP) approximation, leads to the existence of a new type of solitons. We use a set of QHD equations in the third order by the interaction radius (TOIR), which corresponds to the GP equation in a first order by the interaction radius. The solution for the soliton in a form of expression for the particle concentration is obtained analytically. The conditions of existence of the soliton are studied. It is shown what solution exists if the interaction between the particles is repulsive. Particle concentration of order of $10^{12}$-$10^{14}$ $cm^{-3}$ has been achieved experimentally for the BEC, the solution exists if the scattering length is of the order of 1 $\mu$m, which can be reached using the Feshbach resonance. It is one of the limit case of existence of new solution. The corresponding scattering length decrease with the increasing of concentration of particles. The investigation of effects in the TOIR approximation gives a more detail information on interaction potentials between the atoms and can be used for a more detail investigation into the potential structure. 
P. A. Andreev, L. S. Kuzmenkov
cond-mat.quant-gas