Real-Time Feynman Path Integral Realization of Instantons
  In Euclidean path integrals, quantum mechanical tunneling amplitudes are associated with instanton configurations. We explain how tunneling amplitudes are encoded in real-time Feynman path integrals. The essential steps are borrowed from Picard-Lefschetz theory and resurgence theory. 
Aleksey Cherman, Mithat Unsal
hep-th