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We investigate the phase structure of four-dimensional quantum gravity coupled to Ising spins or Gaussian scalar fields by means of numerical simulations. The quantum gravity part is modelled by the summation over random simplicial…

High Energy Physics - Theory · Physics 2009-10-22 J. Ambjorn , Z. Burda , J. Jurkiewicz , C. F. Kristjansen

We analyze the one-loop effects of massive fields on 2-to-2 scattering processes involving gravitons. It has been suggested that in the presence of gravity, any local effective field theory description must break down at the "species…

High Energy Physics - Theory · Physics 2024-08-27 Simon Caron-Huot , Yue-Zhou Li

In this article we review the foundations and the present status of loop quantum gravity. It is short and relatively non-technical, the emphasis is on the ideas, and the flavor of the techniques. In particular, we describe the kinematical…

General Relativity and Quantum Cosmology · Physics 2011-02-02 Hanno Sahlmann

Loop quantum gravity is a physical theory which aims at unifying general relativity and quantum mechanics. It takes general relativity very seriously and modifies it via a quantisation. General relativity describes gravity in terms of…

General Relativity and Quantum Cosmology · Physics 2022-02-02 J. Manuel García-Islas

We investigate a certain distributional extension of the group of spatial diffeomorphisms in Loop Quantum Gravity. This extension, which is given by the automorphisms Aut(P) of the path groupoid P, was proposed by Velhinho and is inspired…

General Relativity and Quantum Cosmology · Physics 2009-11-18 Benjamin Bahr , Thomas Thiemann

We investigate the astrophysical and cosmological implications of the recently proposed idea of a running gravitational coupling on macroscopic scales. We find that when applied to the rotation curves of galaxies, their flatness requires…

High Energy Physics - Phenomenology · Physics 2016-08-15 Orfeu Bertolami , Juan García-Bellido

In this work, we study the classical and quantum properties of the unique commutative Lorentz-covariant connection for loop quantum gravity. This connection has been found after solving the second-class constraints inherited from the…

General Relativity and Quantum Cosmology · Physics 2011-08-12 Marc Geiller , Marc Lachieze-Rey , Karim Noui

We study the separability of the state space of loop quantum gravity. In the standard construction, the kinematical Hilbert space of the diffeomorphism-invariant states is nonseparable. This is a consequence of the fact that the knot-space…

General Relativity and Quantum Cosmology · Physics 2015-06-25 Winston Fairbairn , Carlo Rovelli

Motivated by the conduction properties of graphene discovered and studied in the last decades, we consider the quantum dynamics of a massless, charged, spin 1/2 relativistic particle in three dimensional space-time, in the presence of an…

High Energy Physics - Theory · Physics 2019-12-24 Ivan Morales , Bruno Neves , Zui Oporto , Olivier Piguet

Within the framework of loop quantum cosmology, there exists a semi-classical regime where spacetime may be approximated in terms of a continuous manifold, but where the standard Friedmann equations of classical Einstein gravity receive…

General Relativity and Quantum Cosmology · Physics 2009-11-10 James E. Lidsey

Loop quantum gravity is a mature theory. To proceed to explicit calculations in cosmology, it is necessary to make assumptions and simplifications based on the symmetries of the cosmological setting. Symmetry reduction is especially…

General Relativity and Quantum Cosmology · Physics 2016-08-03 Aurélien Barrau , Boris Bolliet

We present a separable version of Loop Quantum Gravity (LQG) based on an inductive system of cubic lattices. We construct semi-classical states for which the LQG operators -- the flux, the area and the volume operators -- have the right…

General Relativity and Quantum Cosmology · Physics 2009-11-24 Johannes Aastrup , Jesper M. Grimstrup

In this work we investigate the canonical quantization of 2+1 gravity with cosmological constant $\Lambda>0$ in the canonical framework of loop quantum gravity. The unconstrained phase space of gravity in 2+1 dimensions is coordinatized by…

General Relativity and Quantum Cosmology · Physics 2012-08-15 Karim Noui , Alejandro Perez , Daniele Pranzetti

A hidden gauge theory structure of quantum mechanics which is invisible in its conventional formulation is uncovered. Quantum mechanics is shown to be equivalent to a certain Yang-Mills theory with an infinite-dimensional gauge group and a…

High Energy Physics - Theory · Physics 2009-10-31 M. Reuter

We use the non-perturbative gauge field approach to study the effects of spin orbit coupling on the dynamic of magnetic moment. We present a general equation of motion (EOM) which unifies i) the spin orbit coupling effect derived from the…

Mesoscale and Nanoscale Physics · Physics 2007-05-25 S. G. Tan , M. B. A. Jalil , Xiong-Jun Liu

After a brief review of spin networks and their interpretation as wave functions for the (space) geometry, we discuss the renormalisation of the area operator in loop quantum gravity. In such a background independent framework, we propose…

General Relativity and Quantum Cosmology · Physics 2007-05-23 Etera R. Livine , Daniel R. Terno

Till now, the foundation of quantum physics is still mysterious. To explore the mysteries in the foundation of quantum physics, people always take it for granted that quantum processes must be some types of fields/objects on a rigid space.…

General Physics · Physics 2025-10-24 Su-Peng Kou

The restriction to invariant connections in a Friedmann-Robertson-Walker space-time is discussed via the analysis of the Dirac brackets associated with the corresponding gauge fixing. This analysis allows us to establish the proper…

General Relativity and Quantum Cosmology · Physics 2015-05-27 Francesco Cianfrani , Giovanni Montani

Canonical quantum gravity provides insights into the quantum dynamics as well as quantum geometry of space-time by its implications for constraints. Loop quantum gravity in particular requires specific corrections due to its quantization…

General Relativity and Quantum Cosmology · Physics 2015-05-14 Martin Bojowald

We investigate the construction of coherent states for quantum theories of connections based on graphs embedded in a spatial manifold, as in loop quantum gravity. We discuss the many subtleties of the construction, mainly related to the…

General Relativity and Quantum Cosmology · Physics 2015-06-04 Daniele Oriti , Roberto Pereira , Lorenzo Sindoni