  We study the analytic structure of the S-matrix which is obtained from the
reduced Wheeler-DeWitt wave function describing spherically symmetric
gravitational collapse of massless scalar fields. The simple poles in the
S-matrix occur in the Euclidean spacetime, and the Euclidean Wheeler-DeWitt
equation is a variant of the Calogero models, which is discussed in connection
with conformal mechanics and a quantum instanton.
