Two interpretations of thin-shell instantons

Understand

For O(4)-symmetric instantons, there are two complementary interpretations for their analytic continuations.

• One is the nothing-to-something interpretation, where the initial and final hypersurfaces are disconnected by Euclidean manifolds.
• The other is the something-to-something interpretation, introduced by Brown and Weinberg, where the initial and final hypersurfaces are connected by the Euclidean manifold.
• These interpretations have their own pros and cons and hence they are complementary.