QCD unitarity constraints on Reggeon Field Theory

TL;DR

This paper investigates how QCD unitarity constrains Reggeon Field Theory, revealing that common models like BFKL and JIMWLK do not satisfy these constraints, and introduces a toy model that does.

Contribution

It identifies unitarity constraints on QCD Reggeon Field Theory and constructs a toy model satisfying these constraints, contrasting with existing models.

Findings

BFKL, JIMWLK, and Braun's Hamiltonian violate unitarity constraints

A new toy model satisfying unitarity constraints is developed

The toy model approaches a black disk limit at high energy

Abstract

We point out that the $s$-channel unitarity of QCD imposes meaningful constraints on a possible form of the QCD Reggeon Field Theory. We show that neither the BFKL nor JIMWLK nor Braun's Hamiltonian satisfy the said constraints. In a toy, zero transverse dimensional case we construct a model that satisfies the analogous constraint and show that at infinite energy it indeed tends to a "black disk limit" as opposed to the model with triple Pomeron vertex only, routinely used as a toy model in the literature.