A long-standing problem in QFT and quantum gravity is the construction of an âIR-finite" S-matrix. In the gravitational case, the existence of these âinfrared divergencesâ is intimately tied to the âmemory effectâ (i.e. the permanent displacement of test masses due to the passage of a gravitational wave).
In this talk, I shall explain the origin of these connections and illustrate that the construction of an IR-finite S-matrix requires the inclusion of states with memory (which do not lie in the standard Fock space).
In massive QED an elegant solution to this problem was provided by Faddeev and Kulish who constructed an incoming/outgoing Hilbert space of charged particles âdressedâ with memory.
We illustrate the "preferred status'' of such states and their relationship to the superselection/decoherence structure of QED. However, we show that this construction fails [...]
Gautam Satishchandran (Princeton): Infrared Finite Scattering Theory in QFT and Quantum Gravity
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