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We develop the $T$-flow renormalization group scheme to access the low-temperature many-body physics of open quantum systems by literally lowering the temperature of the environment.

We show how to translate a perturbation expansion for the easier to compute time-nonlocal memory kernel $\mathcal{K}$ into a corresponding expansion for the more complicated time-local generator $\mathcal{G}$.

We present intriguing exact relations between quantities that describe the time-evolution of quite generic open quantum systems. Combined with our fixed-point equation this leads to powerful insights into various approximation strategies.

We show that the “trivial” resonant level model actually provides a rich source of examples for interesting dynamics by solving it in 5 different ways.