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UID:1528@qft.physik.hu-berlin.de
DTSTART;TZID=Europe/Berlin:20210127T130000
DTEND;TZID=Europe/Berlin:20210127T140000
DTSTAMP:20210118T100154Z
URL:https://qft.physik.hu-berlin.de/next-seminars/alexander-zhiboedov-cern
 -2/
SUMMARY:Alexander Zhiboedov CERN - 
DESCRIPTION:Prof. Alexander Zhiboedov (CERN)\n\nTitle: Scattering from prod
 uction in 2d\n\nAbstract:\n\nIn 1968\, Atkinson proved the existence of fu
 nctions that satisfy all S-matrix axioms in four spacetime dimensions. His
  proof is constructive and to our knowledge it is the only result of this
  type. Remarkably\, the methods to construct such functions used in the pr
 oof were never implemented in practice. In the talk\, we describe implemen
 tation of these methods in the simpler setting of two-dimensional S-matri
 ces. We solve the problem of reconstructing the scattering amplitude start
 ing from a given particle production probability. We do this by implement
 ing two numerical iterative schemes (fixed-point iteration and Newton's me
 thod)\, which\, by iterating unitarity and dispersion relations\, converg
 e to solutions to the S-matrix axioms. We characterize the region in the a
 mplitude-space in which our algorithms converge\, and discover a fractal 
 structure connected to the so-called CDD ambiguities which we call "CDD fr
 actal". To our surprise\, the question of convergence naturally connects 
 to the recent study of the coupling maximization in the two-dimensional S-
 matrix bootstrap. The methods exposed here pave the way for applications t
 o higher dimensions\, and expose some of the potential challenges that wi
 ll have to be overcome.
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DTSTART:20201025T020000
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