This book studies solutions of the Polubarinova-Galin and Löwner-Kufarev
equations, which describe the evolution of a viscous fluid (Hele-Shaw)
blob, after the time when these solutions have lost their physical
meaning due to loss of univalence of the mapping function involved. When
the mapping function is no longer locally univalent interesting phase
transitions take place, leading to structural changes in the data of the
solution, for example new zeros and poles in the case of rational maps.
This topic intersects with several areas, including mathematical
physics, potential theory and complex analysis. The text will be
valuable to researchers and doctoral students interested in fluid
dynamics, integrable systems, and conformal field theory.