Exact TTbar Deformation of Two-Dimensional Maxwell Theory

We study the partition function of T Tbar -deformed two-dimensional Maxwell theory by solving the relevant flow equation at the level of individual flux sectors. Summing exactly the "instanton" series, we obtain a well-defined expression for the partition function at arbitrary mu. For mu > 0, the spectrum of the theory experiences a truncation and the theory undergoes infinite-order quantum phase transitions associated with the vanishing of Polyakov-loop correlators. For mu < 0, the appearance of nonperturbative contributions in p drastically modifies the structure of the partition function.