  We study two-point functions of local operators and their spectral
representation in UV complete quantum field theories in generic dimensions
focusing on conserved currents and the stress-tensor. We establish the
connection with the central charges of the UV and IR fixed points. We re-derive
c-theorems in 2d and show the absence of their direct analogs in higher
dimensions. We conclude by focusing on quantum field theories with a mass gap.
We study the stress tensor two-particle form factor, derive implications of
unitarity and define concrete bootstrap problems in generic dimensions.
