Status  Confirmed 
Seminar Series  STRLPTENSHE 
Subjects  hepth 
Date  Friday 11 December 2020 
Time  14:00 
Institute  LPTENS 
Seminar Room  GoToMeeting 
Speaker's Last Name  Paulos 
Speaker's First Name  Miguel 
Speaker's Email Address  
Speaker's Institution  ENS, CNRS 
Title  Landau diagrams in AdS and Smatrices from conformal correlators 
Abstract  Quantum field theories in AdS generate conformal correlation functions on the boundary, and in the limit where AdS is nearly flat one should be able to extract an Smatrix from such correlators. We discuss a particularly simple positionspace procedure to do so. It features a direct map from boundary positions to (onshell) momenta and thereby relates cross ratios to Mandelstam invariants. This recipe succeeds in several examples, includes the momentumconserving delta functions, and can be shown to imply the two proposals in arXiv:1607.06109 based on Mellin space and on the OPE data. Interestingly the procedure does not always work: the Landau singularities of a Feynman diagram are shown to be part of larger regions, to be called `bad regions', where the flatspace limit of the Witten diagram diverges. To capture these divergences we introduce the notion of Landau diagrams in AdS. As in flat space, these describe onshell particles propagating over large distances in a complexified space, with a form of momentum conservation holding at each bulk vertex. As an application we recover the anomalous threshold of the fourpoint triangle diagram at the boundary of a bad region. 
arXiv Preprint Number  2007.13745 
Comments  Connection details posted here shortly before the talk 
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