Causality, unitarity and stability in quantum gravity: a non-perturbative perspective

Platania, Alessia

doi:10.1007/jhep09(2022)167

Cited by 23 publications

(9 citation statements)

References 209 publications

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“…RG approaches to quantum gravity like AS fully support and provide a framework for the required Λ behavior discussed in this work, [3,[28][29][30][31]. Quantum corrections (nonperturbative) result in an effective gravity action with a varying CC, Λ, which depends on the characteristics of the system under consideration.…”

Section: Asymptotic Safety (As)mentioning

confidence: 73%

Phenomenological footprints of Λ varying gravity theories inspired from quantum gravity models in the multi-messenger era

Good,

Zarikas

2023

Class. Quantum Grav.

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An interesting phenomenological consequence of $\Lambda$ varying gravity theories inspired by quantum gravity models is reported. The treatment in the present work is quite general and applicable to several different actions with $\Lambda$ varying, especially those used in RG approaches to quantum gravity. An effective gravitational action with a scale varying cosmological constant, $\Lambda$, which depends on the system's characteristics, like the length and the energy density, is the key feature. If the system is an astrophysical object, like a cluster of galaxies, a black hole, etc, non-negligible corrections arise to several observable quantities.Distinctive footprints could refer to luminosity distance and strong/weak lensing measurements, among others. The present study focuses on the SNIa luminosity distance observable.

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Section: Asymptotic Safety (As)mentioning

confidence: 73%

Phenomenological footprints of Λ varying gravity theories inspired from quantum gravity models in the multi-messenger era

Good,

Zarikas

2023

Class. Quantum Grav.

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“…The reason is that the approximation intrinsic to the derivative expansion leads to inverse propagators which are polynomial in the momentum. Hence it is difficult to address questions about stability and the potential presence of ghosts within this approximation [66,67].…”

Section: Derivative and Curvature Expansionmentioning

confidence: 99%

The Functional Renormalization Group in Quantum Gravity

Saueressig¹

2023

Preprint

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The gravitational asymptotic safety program envisions a high-energy completion of the gravitational interactions by an interacting renormalization group fixed point, the Reuter fixed point. The primary tool for investigating this scenario are functional renormalization group equations, foremost the Wetterich equation. This equation implements the idea of the Wilsonian renormalization group by integrating out quantum fluctuations shell-by-shell in momentum space and gives access to the theory's renormalization group flow beyond the realm of perturbation theory. This chapter gives a pedagogical introduction to the gravitational asymptotic safety program with a specific focus on clarifying conceptual points which led to confusion in the past. We provide a step-by-step introduction to the Wetterich equation and its most commonly used non-perturbative approximations. This exposition also introduces recent developments including the minimal essential scheme and N-type cutoffs. The use of the Wetterich equation in explicit computations is illustrated within the Einstein-Hilbert truncation which constitutes the simplest non-perturbative approximation of the gravitational renormalization group flow. We conclude with a brief summary and comments on recent developments originating from other quantum gravity programs.

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“…The potential for stable motion in the presence of interacting ghosts has, of course, been previously considered. (While we will be concerned only with classical theories, we refer to [6,8,[17][18][19][20][21][22][23][24][25][26][27] for proposals at the quantum level.) At the classical level, it has been argued that theories with ghosts can be considered "benign", provided that the runaway is sufficiently mild and the motion can be extended to the infinite future [25,[28][29][30][31].…”

Section: Jcap11(2023)031mentioning

confidence: 99%

Global and local stability for ghosts coupled to positive energy degrees of freedom

Deffayet,

Held,

Mukohyama

et al. 2023

J. Cosmol. Astropart. Phys.

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Negative kinetic energies correspond to ghost degrees of freedom, which are potentially of relevance for cosmology, quantum gravity, and high energy physics. We present a novel wide class of stable mechanical systems where a positive energy degree of freedom interacts with a ghost. These theories have Hamiltonians unbounded from above and from below, are integrable, and contain free functions. We show analytically that their classical motion is bounded for all initial data. Moreover, we derive conditions allowing for Lyapunov stable equilibrium points. A subclass of these stable systems has simple polynomial potentials with stable equilibrium points entirely due to interactions with the ghost. All these findings are fully supported by numerical computations which we also use to gather evidence for stability in various nonintegrable systems.

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Causality, unitarity and stability in quantum gravity: a non-perturbative perspective

Cited by 23 publications

References 209 publications

Phenomenological footprints of Λ varying gravity theories inspired from quantum gravity models in the multi-messenger era

Phenomenological footprints of Λ varying gravity theories inspired from quantum gravity models in the multi-messenger era

The Functional Renormalization Group in Quantum Gravity

Global and local stability for ghosts coupled to positive energy degrees of freedom

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