In this paper we characterize the nonvanishing of the central critical valu
e of the third symmetric power L-functions of irreducible cuspidal automorp
hic representations Pi of GL(2)(A) in terms of the occurrence of Pi in the
spectral decomposition of the tensor product of two automorphic theta repre
sentations on the cubic cover of GL(2)(A), which was constructed by Kazhdan
and Patterson in [KP].