O(N) Quintessence with a Cosine-Type Potential

We propose a quintessence model with a cosine-type potential, in which the scalar field Ф^a possesses an O(N) internal symmetry. The most prominent feature of this model is that it will not reduce to a cosmological constant even when |Ф^a| is spatially uniform and time-independent. Since different value of the potential parameter will lead to different cosmic microwave background anisotropies which may be detectable in the future satellite experiments, one can decide by observations whether the cosine-type quintessence consists of one scalar field or many fields with a symmetry constraint.