Gradient-flowed thermal correlators: how much flow is too much?

TL;DR

This paper investigates the impact of gradient flow on thermal correlators in QCD, identifying conditions under which flow improves data quality without contamination, and providing guidelines for safe application.

Contribution

It offers a perturbative analysis of gradient flow effects on thermal correlators, establishing a threshold for safe flow levels in lattice QCD calculations.

Findings

Gradient flow minimally affects correlators below a certain threshold.

Beyond the threshold, correlators are rapidly contaminated.

Provides a practical prescription for safe gradient flow application.

Abstract

Gradient flow has been proposed in the lattice community as a tool to reduce the sensitivity of operator correlation functions to noisy UV fluctuations. We test perturbatively under what conditions doing so may contaminate the results. To do so, we compute gradient-flowed electric field two-point correlators and stress tensor one- and two-point correlators at finite temperature in QCD. Gradient flow has almost no influence on the value of correlators until a (temperature- and separation-dependent) level of flow is reached, after which the correlator is rapidly compromised. We provide a prescription for how much flow is "safe."