Euclidean quantum gravity
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Gravitational decoherence Open
We discuss effects of loss of coherence in low energy quantum systems caused by or related to gravitation, referred to as gravitational decoherence. These effects, resulting from random metric fluctuations, for instance, promise to be acce…
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Entropy, extremality, euclidean variations, and the equations of motion Open
We study the Euclidean gravitational path integral computing the Rényi entropy and analyze its behavior under small variations. We argue that, in Einstein gravity, the extremality condition can be understood from the variational principle …
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Weak gravity conjecture Open
The weak gravity conjecture holds that in a theory of quantum gravity any gauge force must mediate interactions stronger than gravity for some particles. This statement has surprisingly deep and extensive connections to many different area…
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Aspects of asymptotic safety for quantum gravity Open
We study fixed points of quantum gravity with renormalisation group methods, and a procedure to remove convergence-limiting poles from the flow. The setup is tested within the $f(R)$ approximation for gravity by solving exact recursive rel…
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Global symmetry, Euclidean gravity, and the black hole information problem Open
A bstract In this paper we argue for a close connection between the non-existence of global symmetries in quantum gravity and a unitary resolution of the black hole information problem. In particular we show how the essential ingredients o…
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Quantum Gravity at the Corner Open
We investigate the quantum geometry of a 2d surface S bounding the Cauchy slices of a 4d gravitational system. We investigate in detail for the first time the boundary symplectic current that naturally arises in the first-order formulation…
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Colored discrete spaces: higher dimensional combinatorial maps and quantum gravity Open
In any dimension $D$, the Euclidean Einstein-Hilbert action, which describes gravity in the absence of matter, can be discretized over random discrete spaces obtained by gluing families of polytopes together in all possible ways. In the ph…
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Renormalization and Asymptotic Safety of Gravity in a Multi-Fold Universe: More Tracking of the Standard Model at the Cost of Supersymmetries, GUTs and Superstrings Open
In a multi-fold universe, gravity emerges from Entanglement through the multi-fold mechanisms. As a result, gravity-like effects appear in between entangled particles that they be real or virtual. Long range, massless gravity results from …
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Essential Quantum Einstein Gravity Open
The non-perturbative renormalisation of quantum gravity is investigated allowing for the metric to be reparameterised along the RG flow, such that only the essential couplings constants are renormalised. This allows us to identify a univer…
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On quantum gravity tests with composite particles Open
Models of quantum gravity imply a fundamental revision of our description of position and momentum that manifests in modifications of the canonical commutation relations. Experimental tests of such modifications remain an outstanding chall…
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Implementing quantum Ricci curvature Open
Quantum Ricci curvature has been introduced recently as a new, geometric\nobservable characterizing the curvature properties of metric spaces, without\nthe need for a smooth structure. Besides coordinate invariance, its key\nfeatures are s…
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The Hilbert space of quantum gravity is locally finite-dimensional Open
We argue in a model-independent way that the Hilbert space of quantum gravity is locally finite-dimensional. In other words, the density operator describing the state corresponding to a small region of space, when such a notion makes sense…
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Composite operators in asymptotic safety Open
We study the role of composite operators in the Asymptotic Safety program for quantum gravity. By including in the effective average action an explicit dependence on new sources we are able to keep track of operators which do not belong to…
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Quantum gravity of Kerr-Schild spacetimes and the logarithmic correction to Schwarzschild black hole entropy Open
In the context of effective field theory, we consider quantum gravity with minimally coupled massless particles. Fixing the background geometry to be of the Kerr-Schild type, we fully determine the one-loop effective action of the theory w…
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How to Wick rotate generic curved spacetime Open
It is an article of folklore that the collection of ideas identified as Euclidean quantum gravity may be derived from ordinary Lorentzian signature gravity by the procedure of Wick rotation. This note will attempt to shed some light on thi…
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Spacetime and Gravity are 2D around Planck Scales: A Universal Property of Consistent Quantum Gravity Open
This short paper shows that General Relativity (GR) combined with Quantum Physics implies spacetime and quantum gravity with 2D degrees of freedom at very small scales.The result is obtained independently of any other assumption on the und…
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Four-Derivative Quantum Gravity Beyond Perturbation Theory Open
In this work we investigate the ultraviolet behavior of Euclidean four-derivative quantum gravity beyond perturbation theory. In addition to a perturbative fixed point, we find an ultraviolet fixed point that is non-trivial in all coupling…
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The canonical frame of purified gravity Open
In the recently introduced gauge theory of translations, dubbed Coincident General Relativity (CGR), gravity is described with neither torsion nor curvature in the spacetime affine geometry. The action of the theory enjoys an enhanced symm…
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Form Factors in Quantum Gravity - contrasting non-local, ghost-free gravity and Asymptotic Safety Open
Form factors constitute the key building block when organising the gravitational dynamics in terms of a curvature expansion. They generalise the concept of momentum-dependent couplings to curved spacetime. Moreover, they may capture modifi…
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Towards coarse graining of discrete Lorentzian quantum gravity Open
A first step towards implementing a notion of coarse graining in an\nintrinsically Lorentzian, discrete quantum- gravity approach, namely causal set\nquantum gravity is taken. It makes use of an abstract notion of scale, based on\ncounting…
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Universal Pattern in Quantum Gravity at Infinite Distance Open
Quantum gravitational effects become significant at a cutoff that can be much lower than the Planck scale whenever there is a large number of light fields. This is expected to occur at any perturbative limit of an effective field theory co…
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Complex, Lorentzian, and Euclidean simplicial quantum gravity: numerical methods and physical prospects Open
Evaluating gravitational path integrals in the Lorentzian has been a long-standing challenge due to the numerical sign problem. We show that this challenge can be overcome in simplicial quantum gravity. By deforming the integration contour…
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Coupling Fields to 3D Quantum Gravity via Chern-Simons Theory Open
We propose a mechanism that couples matter fields to three-dimensional quantum gravity, which can be used for theories with a positive or negative cosmological constant. Our proposal is rooted in the Chern-Simons formulation of three-dimen…
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Form Factors in Quantum Gravity - contrasting non-local, ghost-free\n gravity and Asymptotic Safety Open
Form factors constitute the key building block when organising the\ngravitational dynamics in terms of a curvature expansion. They generalise the\nconcept of momentum-dependent couplings to curved spacetime. Moreover, they may\ncapture mod…
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Near-horizon quantum dynamics of 4D Einstein gravity from 2D Jackiw-Teitelboim gravity Open
We study quantum fluctuations in the light-cone metric of the 4D Einstein-Hilbert action via dimensional reduction to Jackiw-Teitelboim (JT) gravity. In particular, we show that, in Einstein gravity, the causal development of a region in f…
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Anomaly freedom in perturbative models of Euclidean loop quantum gravity Open
Euclidean gravity provides an interesting test system for an analysis of\ncosmological perturbations in an effective Hamiltonian constraint with holonomy\nmodifications from loop quantum gravity. This paper presents a discussion of\nscalar…
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Geometric operators in the asymptotic safety scenario for quantum gravity Open
We consider geometric operators, such as the geodesic length and the volume\nof hypersurfaces, in the context of the Asymptotic Safety scenario for quantum\ngravity. We discuss the role of these operators from the Asymptotic Safety\nperspe…
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Perturbatively renormalizable quantum gravity Open
The Wilsonian renormalization group (RG) requires Euclidean signature. The conformal factor of the metric then has a wrong-sign kinetic term, which has a profound effect on its RG properties. In particular, around the Gaussian fixed point,…
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Why Do Elementary Particles Have Such Strange Mass Ratios?—The Importance of Quantum Gravity at Low Energies Open
When gravity is quantum, the point structure of space-time should be replaced by a non-commutative geometry. This is true even for quantum gravity in the infra-red. Using the octonions as space-time coordinates, we construct pre-spacetime,…
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Towards a Unitary, Renormalizable, and Ultraviolet-Complete Quantum Theory of Gravity Open
For any fundamental quantum field theory, unitarity, renormalizability, and\nrelativistic invariance are considered to be essential properties. Unitarity is\ninevitably connected to the probabilistic interpretation of the quantum theory,\n…