  In our previous paper [1, 2], we proposed a probabilistic argument to explain
the reason why the cosmological constant is very small in 4D. It is natural to
ask if the result can be generalized to D-dimension. Moreover, in higher
dimensional theory motivated by string theory the Gauss-Bonnet term plays an
important role. Therefore, in this paper, we generalize our result to arbitrary
D dimensions including the Gauss-Bonnet term. As a result, we have two main
results. We find that the Euclidean action of the bounce, B, describing the
decay of a de Sitter vacuum, is proportional to $\Lambda^{-\frac{1}{2}(D-2)}$,
which has a pole as $\Lambda \rightarrow 0$ where $\Lambda$ is the cosmological
constant of the parent vacuum. This result is similar to the result in 4D. The
other result is that we find a new decay channel, describing up-tunnelling from
anti-de Sitter into de Sitter. The meaning of this new decay channel in the
string landscape should be explored in the future.
