scholarly journals Non-Cauchy surface foliations and their expected connection to quantum gravity theories

2019 ◽  
Vol 1275 ◽  
pp. 012046
Author(s):  
Merav Hadad
Keyword(s):  
Quantum Gravity ◽  
Cauchy Surface ◽  
Gravity Theories

scholarly journals Noisy effects in interferometric quantum gravity tests

2017 ◽  
Vol 15 (08) ◽  
pp. 1740014 ◽  
Author(s):  
F. Benatti ◽  
R. Floreanini ◽  
S. Olivares ◽  
E. Sindici
Keyword(s):  
Quantum Gravity ◽  
Weak Coupling ◽  
Scale Effects ◽  
External Environment ◽  
Planck Scale ◽  
Canonical Commutation Relations ◽  
Commutation Relations ◽  
Photon Propagation ◽  
Gravity Theories ◽  
Planck Scale Effects

Quantum-enhanced metrology is boosting interferometer sensitivities to extraordinary levels, up to the point where table-top experiments have been proposed to measure Planck-scale effects predicted by quantum gravity theories. In setups involving multiple photon interferometers, as those for measuring the so-called holographic fluctuations, entanglement provides substantial improvements in sensitivity. Entanglement is however a fragile resource and may be endangered by decoherence phenomena. We analyze how noisy effects arising either from the weak coupling to an external environment or from the modification of the canonical commutation relations in photon propagation may affect this entanglement-enhanced gain in sensitivity.

scholarly journals POSSIBLE POLARIZATION AND SPIN-DEPENDENT ASPECTS OF QUANTUM GRAVITY

2008 ◽  
Vol 17 (03n04) ◽  
pp. 495-504 ◽  
Author(s):  
D. V. AHLUWALIA ◽  
N. G. GRESNIGT ◽  
ALEX B. NIELSEN ◽  
D. SCHRITT ◽  
T. F. WATSON
Keyword(s):  
Quantum Gravity ◽  
Structure Formation ◽  
Spin Dependence ◽  
Strong Polarization ◽  
Heisenberg Algebras ◽  
Gravity Effects ◽  
Gravity Theories

We argue that quantum gravity theories that carry a Lie-algebraic modification of the Poincaré and Heisenberg algebras inevitably provide inhomogeneities that may serve as seeds for cosmological structure formation. Furthermore, in this class of theories one must expect a strong polarization and spin dependence of various quantum gravity effects.

Renormalization and unitarity in higher derivative and nonlocal gravity theories

2015 ◽  
Vol 30 (03n04) ◽  
pp. 1540005 ◽  
Author(s):  
E. T. Tomboulis
Keyword(s):  
Quantum Gravity ◽  
Fixed Points ◽  
Fourth Order ◽  
Entire Functions ◽  
Gravitational Action ◽  
Asymptotic Safety ◽  
Higher Derivative ◽  
Fixed Order ◽  
Gravity Theories

We review and discuss higher derivative and nonlocal theories of quantum gravity focusing on their UV and unitarity properties. We first consider the general fourth-order gravitational action, then actions containing derivatives up to any given fixed order, and discuss their UV divergences, fixed points and concomitant unitarity issues. This leads to a more general discussion of "asymptotic safety" and unitarity, which motivates the introduction of nonlocal theories containing derivatives to all orders arising from the expansion of entire functions. For such theories good UV behavior is visible at any finite truncation, but unitarity emerges only when derivatives to all orders are included.

scholarly journals A quantized spacetime based on Spin(3,1) symmetry

2016 ◽  
Vol 25 (13) ◽  
pp. 1645004
Author(s):  
Pisin Chen ◽  
Hsu-Wen Chiang ◽  
Yao-Chieh Hu
Keyword(s):  
String Theory ◽  
Quantum Gravity ◽  
Uncertainty Principle ◽  
Loop Quantum Gravity ◽  
Generalized Uncertainty Principle ◽  
Spin Network ◽  
Fundamental Symmetry ◽  
New Type ◽  
Gravity Theories

We introduce a new type of the spacetime quantization based on the spinorial description suggested by loop quantum gravity. Specifically, we build our theory on a string theory inspired [Formula: see text] worldsheet action. Because of its connection with quantum gravity theories, our proposal may in principle link back to string theory, connect to loop quantum gravity where SU(2) is suggested as the fundamental symmetry, or serve as a Lorentzian spin network. We derive the generalized uncertainty principle and demonstrate the holographic nature of our theory. Due to the quantization of spacetime, geodesics in our theory are fuzzy, but the fuzziness is shown to be much below conceivable astrophysical bounds.

scholarly journals Covariant Space-Time Line Elements in the Friedmann-Lemaitre-Robertson-Walker Geometry

2021 ◽  
Author(s):  
David Escors ◽  
Grazyna Kochan
Keyword(s):  
Quantum Gravity ◽  
Uncertainty Principle ◽  
Lorentz Invariance ◽  
Space Time ◽  
Planck Length ◽  
Time Line ◽  
Geometric Uncertainty ◽  
Expected Length ◽  
Gravity Theories ◽  
Line Elements

Most quantum gravity theories endow space-time with a discreet nature by space quantization on the order of Planck length (lp ). This discreetness could be demonstrated by confirmation of Lorentz invariance violations (LIV) manifested at length scales proportional to lp. In this paper, space-time line elements compatible with the uncertainty principle are calculated for a homogeneous, isotropic expanding Universe represented by the Friedmann-Lemaitre-Robertson-Walker solution to General Relativity (FLRW or FRW metric). To achieve this, the covariant geometric uncertainty principle (GeUP) is applied as a constraint over geodesics in FRW geometries. A generic expression for the quadratic proper space-time line element is derived, proportional to Planck length-squared and dependent on two contributions. The first is associated to the energy-time uncertainty, and the second depends on the Hubble function. The results are in agreement with space-time quantization on the expected length orders, according to quantum gravity theories and experimental constraints on LIV.

scholarly journals GRAVITY IN QUANTUM SPACE–TIME

2010 ◽  
Vol 19 (14) ◽  
pp. 2385-2392 ◽  
Author(s):  
GIOVANNI AMELINO-CAMELIA ◽  
NICCOLÒ LORET ◽  
GIANLUCA MANDANICI ◽  
FLAVIO MERCATI
Keyword(s):  
Quantum Gravity ◽  
Gravitational Collapse ◽  
Particle Physics ◽  
Space Time ◽  
Valuable Insight ◽  
Quantum Space ◽  
Particle Propagation ◽  
Gravity Theories

The literature on quantum-gravity-inspired scenarios for the quantization of space–time has so far focused on particle-physics-like studies. This is partly justified by the present limitations of our understanding of quantum gravity theories, but we here argue that valuable insight can be gained through semi-heuristic analyses of the implications for gravitational phenomena of some results obtained in the quantum space–time literature. In particular, we show that the types of description of particle propagation that emerged in certain quantum space–time frameworks have striking implications for gravitational collapse and for the behavior of gravity at large distances.

scholarly journals Time-independence of gravitational Rényi entropies and unitarity in quantum gravity

2021 ◽  
Vol 2021 (10) ◽  
Author(s):  
Donald Marolf ◽  
Zhencheng Wang
Keyword(s):  
Quantum Gravity ◽  
Saddle Points ◽  
Cauchy Surface ◽  
Convergence Condition ◽  
Point Of View ◽  
Back Reaction ◽  
Unitary Evolution ◽  
Invariant Surfaces ◽  
Rényi Entropies ◽  
Renyi Entropies

Abstract The Hubeny-Rangamani-Takayanagi surface γHRT computing the entropy S(D) of a domain of dependence D on an asymptotically AdS boundary is known to be causally inaccessible from D. We generalize this gravitational result to higher replica numbers n > 1 by considering the replica-invariant surfaces (aka ‘splitting surfaces’) γ of real-time replica-wormhole saddle-points computing Rényi entropies Sn(D) and showing that there is a sense in which D must again be causally inaccessible from γ when the saddle preserves both replica and conjugation symmetry. This property turns out to imply the Sn(D) to be independent of any choice of any Cauchy surface ΣD for D, and also that the Sn(D) are independent of the choice of boundary sources within D. This is a key hallmark of unitary evolution in any dual field theory. Furthermore, from the bulk point of view it adds to the evidence that time evolution of asymptotic observables in quantum gravity is implemented by a unitary operator in each baby universe superselection sector. Though we focus here on pure Einstein-Hilbert gravity and its Kaluza-Klein reductions, we expect the argument to extend to any two-derivative theory who satisfies the null convergence condition. We consider both classical saddles and the effect of back-reaction from quantum corrections.

scholarly journals The quantum echo of the early universe

2015 ◽  
Vol 93 (9) ◽  
pp. 968-970 ◽  
Author(s):  
Ana Blasco ◽  
Luis J. Garay ◽  
Mercedes Martín-Benito ◽  
Eduardo Martín-Martínez
Keyword(s):  
Quantum Gravity ◽  
Early Universe ◽  
Space Time ◽  
Quantum Fields ◽  
Gravitational Effects ◽  
History Of ◽  
Gravity Theories

We show that the fluctuations of quantum fields as seen by late comoving observers are significantly influenced by the history of the early Universe, and therefore they transmit information about the nature of space–time in timescales when quantum gravitational effects were non-negligible. We discuss how this may be observable even nowadays and thus used to build falsifiability tests of quantum gravity theories.

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