Quintessence with O ( N ) symmetry

We study a new class of quintessence models, in which the scalar field possesses an O ( N ) internal symmetry. We give a critical condition of instability for the potential against Q ball formation. We find that the most widely used potentials of quintessence do not satisfy the above condition, and therefore, the O ( N ) quintessence with these potentials will not lead to Q ball formation. It is worth noting that the O ( N ) quintessence with a cosine-type potential is especially interesting in that the angular contribution is not negligible.