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 matt er or radiation, depending on the fate of the Q ball. Thus, the spinning co mplex scalar field is usually very difficult to play the role of the dark e nergy. We also show the general condition that the spinning complex scalar field can successfully be the dark energy. (C) 2001 Published by Elsevier S cience B.V.