  The aim of the present work is to exhibit a new proof of the explicit
spectral expansion for the fourth moment of the Riemann zeta-function that was
established by the second named author a decade ago. Our proof is new,
particularly in the sense that it dispenses completely with the Kloostermania,
the spectral theory of sums of Kloosterman sums that was used in the former
proof. The argument is now constructed precisely upon the spectral structure of
the Lie group PSL(2,R). Main ingredients in our argument are the theory of
automorphic representations as well as the harmonic analysis on the big Bruhat
cell. In essence, this work of ours indicates a new way to view the Riemann
zeta-function.
