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Neural S-matrix bootstrap II: solvable 4d amplitudes with particle production

Mehmet Asim Gumus, Damien Leflot, Piotr Tourkine, Alexander Zhiboedov

29/1/26 Published in : arXiv:2601.22145

We study a model for nonperturbative unitarization of the four-point contact scalar amplitude in four dimensions. It is defined through an infinite sum of planar diagrams, constructed using two-particle unitarity and crossing symmetry. We reformulate the problem in terms of a set of nonlinear integral equations obeyed by the single and double discontinuities of the amplitude. We then solve them using a neural-network ansatz trained by minimizing a physics-informed loss functional. We obtain a one-parameter family of amplitudes, which exhibit rich structure: sizeable particle production, nontrivial emergent Regge behavior, Landau curves, a logarithmic decay at high energy and fixed angle. Finally, we go beyond the two-particle-reducible setup by treating the multi-particle data -- supported above the multi-particle Landau curves due to multi-particle unitarity -- as a dynamical variable. We demonstrate that it can be tuned to suppress low-spin particle production -- a phenomenon we call Aks screening -- at the cost of generating larger and oscillatory double spectral density in the multi-particle region.

Entire article

Phase I & II research project(s)

  • String Theory
  • Field Theory

Phase III direction(s)

  • Holography and bulk-boundary correspondence

Energy correlators in four-dimensional gravity

Quantum Invariants of Ribbon Surfaces in 4-Dimensional 2-Handlebodies

  • Leading house

  • Co-leading house


The National Centres of Competence in Research (NCCRs) are a funding scheme of the Swiss National Science Foundation

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