Q-balls in atomic Bose-Einstein condensates

Relativistic scalar field theories with a conserved global charge Q often possess (meta)stable spherically symmetric soliton solutions, called Q-balls. We elaborate on the perfect formal analogy which exists between Q-balls, and spherically symmetric solitons in certain non-relativistic atomic Bose-Einstein condensates, for which the dominant interatomic interaction can be tuned attractive. The stability of such atomic Q-balls depends on higher-order interatomic interactions, which can render the Q-balls absolutely stable for large Q. In a harmonic trap, present in existing experiments, the Q-ball solution is modified in an essential way. If the trap is significantly prolongated in one direction, however, then genuine solitons do appear, and some of the Q-ball properties studied in a relativistic cosmological context, such as their formation and collisions, can also be addressed experimentally.