Difficulty of a spinning complex scalar field to be dark energy

We comment on the possibility of a spinning complex scalar field to be dark energy. We show that it deforms (almost) completely into a nontopological soliton state, a Q ball, and the equation of state becomes that of the matter or radiation, depending on the fate of the Q ball. Thus, the spinning complex scalar field is usually very difficult to play the role of the dark energy. We also show the general condition that the spinning complex scalar field can successfully be the dark energy. (C) 2001 Published by Elsevier Science B.V.