Evidence for Maximal Acceleration and Singularity Resolution in Covariant Loop Quantum Gravity

Rovelli, Carlo; Vidotto, Francesca

doi:10.1103/physrevlett.111.091303

Cited by 60 publications

(45 citation statements)

References 37 publications

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“…30,31 Recently it has been found in loop quantum gravity as well. 32 It is also invoked to regularize black hole entropy. 33 Other classical and quantum arguments were used to support the existence of MA.…”

Section: Introductionmentioning

confidence: 99%

Unruh temperature with maximal acceleration

Benedetto

Feoli

2015

Mod. Phys. Lett. A

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Section: Introductionmentioning

confidence: 99%

Unruh temperature with maximal acceleration

Benedetto

Feoli

2015

Mod. Phys. Lett. A

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“…The classical curvature singularity at the center of BHs is cured in the quantum theory by nonperturbative effects. In Loop Quantum Gravity singularity resolution has been studied extensively [10,11,12]. Quantum discreteness plays a fundamental role: this is not just a space discreteness, but a spacetime discreteness, that modifies both the kinematics and the dynamics of the theory.…”

Section: Quantum Gravitymentioning

confidence: 99%

Quantum Insights on Primordial Black Holes as Dark Matter

Vidotto¹

2018

Proceedings of 2nd World Summit: Exploring the Dark Side of the Universe — PoS(EDSU2018)

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A recent understanding on how quantum effects may affect black-hole evolution opens new scenarios for dark matter, in connection with the presence of black holes in the very early universe. Quantum fluctuations of the geometry allow for black holes to decay into white holes via a tunnelling. This process yields to an explosion and possibly to a long remnant phase, that cures the information paradox. Primordial black holes undergoing this evolution constitute a peculiar kind of decaying dark matter, whose lifetime depends on their mass M and can be as short as M 2 . As smaller black holes explode earlier, the resulting signal have a peculiar fluence-distance relation. I discuss the different emission channels that can be expected from the explosion (sub-millimetre, radio, TeV) and their detection challenges. In particular, one of these channels produces an observed wavelength that scales with the redshift following a unique flattened wavelength-distance function, leaving a signature also in the resulting diffuse emission. I conclude presenting the first insights on the cosmological constraints, concerning both the explosive phase and the subsequent remnant phase.

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“…The first of them is, obviously, the fact that the big bang singularity is systematically removed (and there are good hints that this is a general feature of LQG [7]). Second, this approach has been extended to non-flat FLRW metrics as well as to anisotropic models such as Bianchi models, to show that the bounce remains [4] (note that the presence of the bounce is robust against different sort of classical content of the universe since it is here a purely quantum gravitational feature).…”

Section: Pos(ffp14)161mentioning

confidence: 99%

A brief overview of loop quantum cosmology

Grain

2016

Proceedings of Frontiers of Fundamental Physics 14 — PoS(FFP14)

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Loop quantum cosmology (a symmetry-reduced quantum model of the Universe inspired by loop quantum gravity) extends the inflationary paradigm to the Planck era: the big bang singularity is replaced by a quantum bounce naturally followed by inflation. Testing for these models requires to compute the amount of cosmological perturbations produced in this quantum background and subsequently derives their footprints on the cosmic microwave background. This proceedings proposes a very brief summary of this road from quantum gravity to cosmological observables, focusing on the case of a loop-quantum model of flat FLRW spaces with cosmological perturbations. The background evolution, passing through a bounce, is first presented. The case of cosmic inhomogeneities in a perturbative treatment about a quantum background are then discussed (with an emphasis on two specific theoretical constructions), and there respective predictions in terms of primordial power spectra for the tensor modes are outlined. PoS(FFP14)161A brief overview of loop quantum cosmology Julien GrainIntroduction-Loop quantum cosmology (LQC) [1] is a tentative approach to built a quantum model of the Universe inspired by the ideas of loop quantum gravity (LQG) -a non-perturbative quantization of general relativity-[2], thus allowing for extending the inflationary paradigm to the Planck era where quantum gravity effects are no more negligible. This approach relies on minisuperspace ideas: the entire phase space of general relativity is reduced thanks to the isotropy and homogeneity symmetries, meaning that only FLRW metric are considered. This reduced phase space is then quantized using the loop representation. At a quantum level, the big bang singularity issue is solved for the transition to the null volume is forbidden, leading to the replacement of the big bang singularity by a quantum big bounce. This is understood at a more effective level by a regularization of the curvature. Classically, the curvature can be computed from holonomies evaluated around a plaquette and then, by shrinking the area of the plaquette to zero. (The FLRW space can be paved by identical plaquettes thanks to isotropy and homogeneity.) However, the kinematical Hilbert space in LQG is given by eigenstates of geometric (area and volume) operators which have discrete spectra. This leads to a minimal area gap and the area of the plaquette around which holonomies are evaluated cannot be shrinked to zero anymore, thus preventing the curvature to diverge. This is captured in the effective, modified Friedmann equation (for a flat FLRW metric with holonomy correction only):, with ρ c a maximal energy density precisely set by the minimal area gap (ρ c is of the order of the Planck energy density, though its explicit value depends on the value of the Barbero-Immirzi parameter, γ). In the effective picture, the bounce occurs when the Hubble parameter, H := (ȧ/a), vanishes, that is when the energy density of the content of the universe reaches ρ c . The classical equation is recovered for ρ...

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Evidence for Maximal Acceleration and Singularity Resolution in Covariant Loop Quantum Gravity

Abstract: A simple argument indicates that covariant loop gravity (spinfoam theory) predicts a maximal acceleration, and hence forbids the development of curvature singularities. This supports the results obtained for cosmology and black holes using canonical methods.

Cited by 60 publications

References 37 publications

Unruh temperature with maximal acceleration

Unruh temperature with maximal acceleration

Quantum Insights on Primordial Black Holes as Dark Matter

A brief overview of loop quantum cosmology

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