Abstract

S-matrix elements in flat space can be obtained from a large AdS-radius limit of certain CFT correlators. We present a method for constructing CFT operators which create incoming and outgoing scattering states in flat space. This is done by taking the flat limit of bulk operator reconstruction techniques. Using this method, we obtain explicit expressions for incoming and outgoing U(1) gauge fields. Weinberg soft photon theorems then follow from Ward identites of conserved CFT currents. In four bulk dimensions, gauge fields on AdS can be quantized with standard and alternative boundary conditions. Changing the quantization scheme corresponds to the S-transformation of SL(2, ℤ) electric-magnetic duality in the bulk. This allows us to derive both, the electric and magnetic soft photon theorems in flat space from CFT physics.

Highlights

  • Despite much progress in the understanding of quantum gravity in asymptotically Antide Sitter spaces [1, 2], good insight into a holographic description of gravity in Minkowski space is still elusive

  • We present a method for constructing CFT operators which create incoming and outgoing scattering states in flat space

  • In this note we report on results which aim to further clarify the structure of holography in asymptotically flat space-times making use of the large radius limit of AdS/CFT

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Summary

Introduction

Despite much progress in the understanding of quantum gravity in asymptotically Antide Sitter spaces [1, 2], good insight into a holographic description of gravity in Minkowski space is still elusive. We show that for the case of a U(1) gauge theory, Weinberg soft theorems can be understood as arising from Ward identities of a CFT in the strict large N limit. This will give a formula for scattering amplitudes of massive and massless scalars in terms of CFT correlation functions. We reconstruct scattering amplitudes of a theory in asymptotically flat spacetimes from the correlators of a conformal field theory in one lower dimension This task has been the subject of much work in the literature [4,5,6,7, 12, 21]. We will focus on the case of bulk scalar fields, leaving the discussion of gauge theories for section 3

Scattering amplitudes in flat space-time
Flat limit of HKLL operator: massless
Flat limit of HKLL operator: massive
Mapping of asymptotic regions
Photon scattering states
Inequivalent quantization schemes of scalar fields in AdS
Flat limit: magnetic boundary conditions
Flat limit: electric boundary conditions
Coulombic source terms
From conformal Ward identities to Weinberg soft theorems
Ward identities in CFT
Weinberg soft theorems as symmetries of the S-matrix
From CFT physics to soft theorems
From CFT physics to magnetic soft theorems
Conclusions
A Complex coordinates on S2
B Scalar HKLL operators
Reconstruction with “magnetic” boundary conditions
E AdS Liénard-Wiechert potentials
F Sample calculations
One-to-one scattering
One particle-state normalization
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