Tunneling in Λ decaying cosmologies and the cosmological constant problem -: art. no. 063514.

The tunneling rate, with an exact prefactor, is calculated to first order in (h) over bar for an empty closed Friedmann-Robertson-Walker universe with a decaying cosmological term Lambda similar to R-m (R is the scale factor and m is a parameter 0 less than or equal to m less than or equal to 2). This model is equivalent to a cosmology with the equation of state p(chi)=(m/3-1)rho(chi). The calculations are performed by applying the dilute-instanton approximation on the corresponding Duru-Kleinert path integral. It is shown that the highest tunneling rate occurs for m = 2 corresponding to the cosmic string matter universe. The most probable cosmological term obtained, such as the one obtained by Strominger, accounts for a possible solution to the cosmological constant problem. [S0556-2821(99)03016-7].