Quantum gravity: a progress report

Carlip, Steven

doi:10.1088/0034-4885/64/8/301

Cited by 356 publications

(427 citation statements)

References 354 publications

(484 reference statements)

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“…We refer to the range of couplings satisfying all these requirements 25 as the DTsurface in the five-dimensional space {a, x, ξ , z 3 , z 2 }. In figure 2, we display a small portion 25 We do not include the constraints of stability under radiative corrections (section 8) or lying in the catchment basis of the UVFP (section 9).…”

Section: Jhep05(2016)185mentioning

confidence: 99%

Induced gravity II: grand unification

Einhorn

Jones

2016

J. High Energ. Phys.

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As an illustration of a renormalizable, asymptotically-free model of induced gravity, we consider an SO(10) gauge theory interacting with a real scalar multiplet in the adjoint representation. We show that dimensional transmutation can occur, spontaneously breaking SO(10) to SU(5)⊗U(1), while inducing the Planck mass and a positive cosmological constant, all proportional to the same scale v. All mass ratios are functions of the values of coupling constants at that scale. Below this scale (at which the Big Bang may occur), the model takes the usual form of Einstein-Hilbert gravity in de Sitter space plus calculable corrections. We show that there exist regions of parameter space in which the breaking results in a local minimum of the effective action giving a positive dilaton (mass) 2 from two-loop corrections associated with the conformal anomaly. Furthermore, unlike the singlet case we considered previously, some minima lie within the basin of attraction of the ultraviolet fixed point. Moreover, the asymptotic behavior of the coupling constants also lie within the range of convergence of the Euclidean path integral, so there is hope that there will be candidates for sensible vacua. Although open questions remain concerning unitarity of all such renormalizable models of gravity, it is not obvious that, in curved backgrounds such as those considered here, unitarity is violated. In any case, any violation that may remain will be suppressed by inverse powers of the reduced Planck mass.

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Section: Jhep05(2016)185mentioning

confidence: 99%

Induced gravity II: grand unification

Einhorn

Jones

2016

J. High Energ. Phys.

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“…One could try to choose a specific gauge in accordance to the invariance associated with the algebra (3.8)-(3.10), then solve the constraints (3.4) and (3.5), and finally quantize the resulting system with the "true" degrees of freedom. It turns out that in general the final equations are tractable only perturbatively, and lead to ultraviolet divergences (for further details see, for example, [13,14]). …”

Section: Time In General Relativitymentioning

confidence: 99%

Time Paradox in Quantum Gravity

Macı́as

Quevedo

Quantum Gravity

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Abstract. The aim of this work is to review the concepts of time in quantum mechanics and general relativity to show their incompatibility. We show that the absolute character of Newtonian time is present in quantum mechanics and also partially in quantum field theories which consider the Minkowski metric as the background spacetime. We discuss the problems which this nondynamical concept of time causes in general relativity that is characterized by a dynamical spacetime. Mathematics Subject Classification (2000). Primary 46N50; Secondary 85A99.

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“…There are many different approaches to quantum gravity [23][24][25] based on different principles. Some approaches, such as loop quantum gravity, 26 stress the gauge structure from the diffeomorphism of the spacetime and try to build a quantum theory where the whole space-time is emergent.…”

Section: The Strategy Of Our Approachmentioning

confidence: 99%

Emergence of helicity ±2 modes (gravitons) from qubit models

Wen

2012

Nuclear Physics B

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Gauge symmetry is commonly regarded as one of the founding principles of nature. But recent studies of topological/quantum order suggest that gauge symmetry can emerge as a low energy property of a qubit model that have no gauge symmetry at all at lattice scale. This suggests that gauge symmetry may not be a founding principle, but merely a property of a quantum ground state with long range quantum entanglements.The general equivalence principle and the associated diffeomorphism gauge symmetry are also regarded as a founding principles of nature. So one may wonder, can diffeomorphism gauge symmetry also emerge as a low energy property of certain topological/quantum order in a qubit model? In this paper, we designed qubit models (or quantum spin models) on 3D lattice and showed that, for the first time, gapless helicity ±2 excitations (ie the gravitons) can emerge as the only low energy excitation in our models. We showed that the emergence of gapless helicity ±2 excitations in our models leads to the emergence of, at least, linearized diffeomorphism gauge symmetry hµν → hµν + ∂µfν + ∂νfµ at low energies.In the first qubit model (called the L-type model), we show that helicity ±2 gapless excitations appear as the only type of low energy excitations using a reliable semiclassical approach. The dispersion of the gapless helicity ±2 is found to be ǫ k ∝ |k| 3 . The appearance of the gapless helicity ±2 modes suggests that the ground state of the qubit model is a new state of matter. In the second model (called the N-type model) the collective modes are strongly interacting and there is no reliable approach to understand its low energy dynamics. Using a spin-wave/quantum-freeze approach (which is shown to reproduce the correct emergent U (1) gauge theory in a quantum rotor model), we argue that the second model may contain helicity ±2 gapless excitations as the only type of low energy excitations with a linear dispersion ω ∝ k.Both models have emergent low energy diffeomorphism gauge symmetry which leads to the associated gapless helicity ±2 excitations. We believe that those properties are topologically robust: any translation invariant perturbations cannot break the emergent diffeomorphism gauge symmetry and cannot generate a gap for those helicity ±2 excitations. Our results shed light on the quest to find a quantum theory of gravity -a quantum model with a finite cutoff whose ground state supports gravitons (ie helicity ±2 gapless excitations with a linear ǫ k ∝ |k| dispersion). Contents

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Quantum gravity: a progress report

Cited by 356 publications

References 354 publications

Induced gravity II: grand unification

Induced gravity II: grand unification

Time Paradox in Quantum Gravity

Emergence of helicity ±2 modes (gravitons) from qubit models

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