Analytic Perturbation Theory for QCD observables

TL;DR

This paper develops an analytic perturbation theory for QCD that provides a unified, singularity-free framework for analyzing observables in both Euclidean and Minkowskian regions, improving convergence and consistency in the infrared region.

Contribution

It introduces a self-consistent scheme called Analytic Perturbation Theory (APT) that relates effective coupling functions and non-power expansions across space- and time-like domains, incorporating quark thresholds.

Findings

The global APT scheme yields slightly different results for the strong coupling constant compared to traditional methods.

The approach removes unphysical singularities from QCD observables, enhancing convergence in the infrared.

Preliminary estimates show a few percent difference in the five-flavor region for the QCD coupling constant.

Abstract

The connection between ghost-free formulations of RG-invariant perturbation theory in the both Euclidean and Minkowskian regions is studied. Our basic tool is the "double spectral representation", similar to definition of Adler function, that stems from first principles of local QFT. It relates real functions defined in the Euclidean and Minkowskian regions. On this base we establish a simple relation between -- The trick of resummation of the $\pi^2$-terms (known from early 80s) for the invariant QCD coupling and observables in the time-like region and -- Invariant Analytic Approach (devised a few years ago) with the "analyticized" coupling $\alpha_{\rm an}(Q^2)$ and nonpower perturbative expansion for observables in the space-like domain which are free of unphysical singularities . As a result, we formulate a self-consistent scheme, Analytic Perturbation Theory (APT), that relates a renorm-invariant, effective coupling functions $\alpha_{an}(Q^2) $ and $\tilda{alpha}(s),$ as well as non-power perturbation expansions for observables in both space- and time-like domains, that are free of extra singularities and obey better convergence in the infrared region. Then we consider the quark threshold crossing and devise a global APT scheme for the data analysis in the whole accessible space-like and time-like domain with various numbers of active quarks. Preliminary estimates indicate that this global scheme produces results a bit different, sometimes even in the five-flavour region, on a few per cent level for $\bar{\alpha}_s$ -- from the usual one, thus influencing the total picture of the QCD parameter correlation.