Abstract

We define Mellin amplitudes for the fermion-scalar four point function and the fermion four point function. The Mellin amplitude thus defined has multiple components each associated with a tensor structure. In the case of three spacetime dimensions, we explicitly show that each component factorizes on dynamical poles onto components of the Mellin amplitudes for the corresponding three point functions. The novelty here is that for a given exchanged primary, each component of the Mellin amplitude may in general have more than one series of poles. We present a few examples of Mellin amplitudes for tree-level Witten diagrams and tree-level conformal Feynman integrals with fermionic legs, which illustrate the general properties.

Highlights

  • From the pioneering work of Mack [1, 2], followed up on later by Penedones and several others [3,4,5,6,7], we understand that Mellin space provides us with a natural representation to study conformal correlation functions

  • We have introduced Mellin amplitudes associated with correlators of spin half fermions and scalars

  • Such Mellin amplitudes have multiple components, each component being associated with an element of a chosen basis of tensor structures

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Summary

Introduction

From the pioneering work of Mack [1, 2], followed up on later by Penedones and several others [3,4,5,6,7], we understand that Mellin space provides us with a natural representation to study conformal correlation functions. The three point function of two fermions and a boson has multiple tensor structures This results in each component of the Mellin amplitude having more than one distinct series (two in our case) of poles corresponding to each primary operator exchanged in the OPE in a given channel. It must be noted that the pole structure of the Mellin amplitude is related to the choice of basis and is tunable as such After this preliminary analysis of the properties of the Mellin amplitude, we compute some Mellin amplitudes corresponding to tree level Witten diagrams and tree level conformal Feynman integrals. These examples illustrate the generic predictions on the pole structure considering the parity of the three point functions in each case. Calculations, methods and a short review of fermions in AdS are provided in the appendices

Review
Tensor structures
Definition
Pole structure: fermion-scalar four point function
Crossed channel
Pole structure: four fermion correlator
Witten diagrams
Contact Witten diagram
Scalar exchange Witten diagram with two external fermions
Scalar exchange Witten diagram with four external fermions
Spinor exchange Witten diagrams
Conformal Feynman integrals
Fermion-scalar four point function: contact diagram
Result
Fermion four point function: contact interaction
Fermion four point function: scalar propagator
Discussion
Counting tensor structures
Tensor structures: fermion four point function
Reduced Mellin amplitude and Mellin amplitude for the four fermion correlator
Mixed fermion scalar conformal blocks
Crossed channel poles in the four fermion Mellin amplitude
Fermions in AdS
Spinor exchange in AdS
C Feynman diagrams
Full Text
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