Stabilizing the gravitational action and Coleman's solution to the   cosmological constant problem
  We use the 5-th time action formalism introduced by Halpern and Greensite to stabilize the unbounded Euclidean 4-D gravity in two simple minisuperspace models. In particular, we show that, at the semiclassical level ($\hbar \rightarrow 0$), we still have as a leading saddle point the $S^4$ solution and the Coleman peak at zero cosmological constant, for a fixed De Witt supermetric. At the quantum (one-loop) level the scalar gravitational modes give a positive semi-definite Hessian contribution to the 5-D partition function, thus removing the Polchinski phase ambiguity. 
Alberto Carlini and Maurizio Martellini