Renormalization group flow and fixed point of the lattice topological charge in the 2-d O(3) sigma-model

TL;DR

This paper investigates the renormalization group flow of the lattice topological charge in the 2D O(3) sigma-model, demonstrating that quantum fluctuations diminish after a few iterations, leading to a good approximation of the fixed point.

Contribution

It introduces a step-by-step renormalization group analysis of the lattice topological susceptibility, including a Symanzik-improved charge, and assesses the approximation validity for the fixed point.

Findings

Quantum fluctuations are suppressed after three RG iterations.

The Symanzik-improved charge effectively reduces renormalizations.

Assumption of slowly varying fields does not accurately approximate the fixed point.

Abstract

We study the renormalization group evolution up to the fixed point of the lattice topological susceptibility in the 2-d O(3) non-linear sigma-model. We start with a discretization of the continuum topological charge by a local charge density, polynomial in the lattice fields. Among the different choices we propose also a Symanzik--improved lattice topological charge. We check step by step in the renormalization group iteration the progressive dumping of quantum fluctuations, which are responsible for the additive and multiplicative renormalizations of the lattice topological susceptibility with respect to the continuum definition. We find that already after three iterations these renormalizations are negligible and an excellent approximation of the fixed point is achieved. We also check by an explicit calculation that the assumption of slowly varying fields in iterating the renormalization group does not lead to a good approximation of the fixed point charge operator.