Abstract

In this paper we encode the perturbative BFKL leading logarithmic resummation, relevant for the Regge limit behavior of QCD scattering amplitudes, in the IR-regulated effective action which satisfies exact functional renormalization group equations. This is obtained using a truncation with a specific infinite set of non local vertices describing the multi-Regge kinematics (MRK). The goal is to use this framework to study, in the high energy limit and at larger transverse distances the transition to a much simpler effective local reggeon field theory, whose critical properties were recently investigated in the same framework. We perform a numerical analysis of the spectrum of the BFKL Pomeron deformed by the introduction of a Wilsonian infrared regulator to understand the properties of the leading poles (states) contributing to the high energy scattering.

Highlights

  • Of large distances, for which still very little can be derived from a fundamental QCD description

  • Some time ago [1, 2] we have started a program which aims at finding an interpolation between the perturbative QCD Pomeron (BFKL Pomeron) and the nonperturbative soft Pomeron which describes elastic proton-proton scattering at high energies

  • We have studied the flow of the so called Reggeon Field Theory (RFT) for a single Pomeron field and for a Pomeron coupled to an Odderon field, in particular the critical universal properties of these two QFTs and some features of the flow associated to the scale change

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Summary

The setup: the LO BFKL equation

We begin by recalling the massless color singlet BFKL equation [12,13,14,15] in the leading approximation (MRK). Let us start with the amputated BFKL Green’s function G(q , q − q ; q , q − q |ω) It is obtained as an infinite sum of ladder diagrams and satisfies the integral (Bethe-Salpeter like) equation: GBFKL(q , q − q ; q , q − q |ω) = KBFKL(q, q − q ; q , q − q ). The analytic expression of the LO BFKL kernel (the so called real part, induced by rapidity separated real gluon emissions) has the form: KBFKL(q , q − q ; q. This kernel is illustrated in figure 2a: The gluon trajectory function has the form:. The sum of the discrete set and the continuous part of eigenfunctions defines a complete set This Green’s function Gk satisfies the equation.

Regulators and the τ -derivative of the BFKL Geen’s function
An effective field theory for deriving the BFKL Green’s function
Elements of the field theory
RG flow equations
Two-point function
Vertex functions
Flow equation for the 4-point function
Flow equation for the 5-point and 6-point functions
Introducing the running coupling
A nonlinear equation for the τ -derivative of 4-point function
Eigenvalues and eigenfunctions in the forward direction
Running coupling
Summary and outlook
A Rapidity-dependence of propagators
Full Text
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