Anomaly freedom in effective Loop Quantum Cosmology: pedagogical summary and generalized holonomy corrections

TL;DR

This paper thoroughly investigates the anomaly freedom of effective loop quantum cosmology with generalized holonomy corrections, emphasizing the importance of counter-terms for algebra closure and clarifying the conditions for consistent perturbative quantum gravity models.

Contribution

It provides a detailed analysis of anomaly freedom in effective loop quantum cosmology, highlighting the role of counter-terms and exploring ambiguities in holonomy corrections.

Findings

Counter-terms are essential for anomaly freedom in scalar perturbations.

Multiple methods can achieve a first-class constraint algebra, but ambiguities arise.

Detailed calculations clarify the assumptions needed for algebra closure.

Abstract

The issue of consistency is crucial in quantum gravity. It has recently been intensively addressed for effective symmetry-reduced models. In this article, we exhaustively study the anomaly freedom of effective loop quantum cosmology with generalized holonomy corrections, considering loop correction of the constraints at the perturbative order. We pedagogically explain why, although the holonomy correction -- including the details of the chosen scheme -- applied on the background part of the constraints is crucial, it becomes irrelevant when implemented on perturbative expansions, in the sense that all consequences are "absorbed" in the counter-terms used for the regularization. The possibility of closing the algebra of constraints without counter-terms is also studied. It is argued that, although enforcing a first-class algebra is a strong requirement, this can be achieved in several different ways, often overlooked, which generates ambiguities on the restriction of the form of the generalized holonomy correction. Those ambiguities are examined in details, leading to the conclusion that the consistency of the effective theory for cosmological perturbations, especially when considering scalar modes, cannot be achieved without counter-terms. We also take the opportunity of this work to clarify, as much as possible, all the required steps so that future works have a clear material at disposal. In particular, a highly detailed calculation of all the brackets is provided, emphasizing the (usually implicit) assumptions, hypotheses and manipulations required to ensure the closure of the algebra. Prospects for future works are underlined.