scholarly journals Signature change in loop quantum gravity: Two-dimensional midisuperspace models and dilaton gravity

2017 ◽  
Vol 95 (12) ◽  
Author(s):  
Martin Bojowald ◽  
Suddhasattwa Brahma
Keyword(s):  
Quantum Gravity ◽  
Loop Quantum Gravity ◽  
Two Dimensional ◽  
Dilaton Gravity ◽  
Signature Change

scholarly journals Signature change in two-dimensional black-hole models of loop quantum gravity

2018 ◽  
Vol 98 (2) ◽  
Author(s):  
Martin Bojowald ◽  
Suddhasattwa Brahma
Keyword(s):  
Black Hole ◽  
Quantum Gravity ◽  
Loop Quantum Gravity ◽  
Two Dimensional ◽  
Signature Change ◽  
Dimensional Black Hole

scholarly journals Quantum gravity and the cosmological constant: Lessons from two-dimensional dilaton gravity

2013 ◽  
Vol 87 (8) ◽  
Author(s):  
Jan Govaerts ◽  
Simone Zonetti
Keyword(s):  
Quantum Gravity ◽  
Cosmological Constant ◽  
Two Dimensional ◽  
Dilaton Gravity

scholarly journals Dilaton gravity, Poisson sigma models and loop quantum gravity

2009 ◽  
Vol 26 (3) ◽  
pp. 035018 ◽  
Author(s):  
Martin Bojowald ◽  
Juan D Reyes
Keyword(s):  
Quantum Gravity ◽  
Sigma Models ◽  
Loop Quantum Gravity ◽  
Dilaton Gravity

scholarly journals Quantum Holography from Fermion Fields

2021 ◽  
Vol 3 (3) ◽  
pp. 576-591
Author(s):  
Paola Zizzi
Keyword(s):  
Quantum Gravity ◽  
Degrees Of Freedom ◽  
Loop Quantum Gravity ◽  
Boundary Surface ◽  
Holographic Principle ◽  
Dimensional Sphere ◽  
Two Dimensional ◽  
Fuzzy Sphere ◽  
Fermion Fields ◽  
Planck Unit

In this paper, we demonstrate, in the context of Loop Quantum Gravity, the Quantum Holographic Principle, according to which the area of the boundary surface enclosing a region of space encodes a qubit per Planck unit. To this aim, we introduce fermion fields in the bulk, whose boundary surface is the two-dimensional sphere. The doubling of the fermionic degrees of freedom and the use of the Bogolyubov transformations lead to pairs of the spin network’s edges piercing the boundary surface with double punctures, giving rise to pixels of area encoding a qubit. The proof is also valid in the case of a fuzzy sphere.

scholarly journals Quantum gravity near the apparent horizon and two-dimensional dilaton gravity

1998 ◽  
Vol 57 (4) ◽  
pp. 2415-2420
Author(s):  
Ichiro Oda
Keyword(s):  
Quantum Gravity ◽  
Apparent Horizon ◽  
Two Dimensional ◽  
Dilaton Gravity

scholarly journals Quantum Holography from Fermion Fields

2021 ◽  
Author(s):  
Paola Zizzi
Keyword(s):  
Quantum Gravity ◽  
Degrees Of Freedom ◽  
Loop Quantum Gravity ◽  
Boundary Surface ◽  
Dimensional Sphere ◽  
Two Dimensional ◽  
Fuzzy Sphere ◽  
Fermion Fields ◽  
Planck Unit ◽  
Bogoliubov Transformations

We demonstrate, in the context of Loop Quantum Gravity, the Quantum Holographic Principle, according to which the area of the boundary surface enclosing a region of space encodes a qubit per Planck unit. To this aim, we introduce fermion fields in the bulk, whose boundary surface is the two-dimensional sphere. The doubling of the fermionic degrees of freedom and the use of the Bogoliubov transformations lead to pairs of spin network’s edges piercing the boundary surface with double punctures, giving rise to pixels of area encoding a qubit. The proof is also valid in the case of a fuzzy sphere.

scholarly journals Some implications of signature-change in cosmological models of loop quantum gravity

2015 ◽  
Vol 2015 (08) ◽  
pp. 052-052 ◽  
Author(s):  
Martin Bojowald ◽  
Jakub Mielczarek
Keyword(s):  
Quantum Gravity ◽  
Loop Quantum Gravity ◽  
Cosmological Models ◽  
Signature Change

scholarly journals Black-Hole Models in Loop Quantum Gravity

Universe ◽  
2020 ◽  
Vol 6 (8) ◽  
pp. 125
Author(s):  
Martin Bojowald
Keyword(s):  
Black Hole ◽  
Quantum Gravity ◽  
Loop Quantum Gravity ◽  
Space Time ◽  
Classical Solutions ◽  
General Covariance ◽  
White Hole ◽  
Signature Change ◽  
Generalized Covariance ◽  
Line Elements

Dynamical black-hole scenarios have been developed in loop quantum gravity in various ways, combining results from mini and midisuperspace models. In the past, the underlying geometry of space-time has often been expressed in terms of line elements with metric components that differ from the classical solutions of general relativity, motivated by modified equations of motion and constraints. However, recent results have shown by explicit calculations that most of these constructions violate general covariance and slicing independence. The proposed line elements and black-hole models are therefore ruled out. The only known possibility to escape this sentence is to derive not only modified metric components but also a new space-time structure which is covariant in a generalized sense. Formally, such a derivation is made available by an analysis of the constraints of canonical gravity, which generate deformations of hypersurfaces in space-time, or generalized versions if the constraints are consistently modified. A generic consequence of consistent modifications in effective theories suggested by loop quantum gravity is signature change at high density. Signature change is an important ingredient in long-term models of black holes that aim to determine what might happen after a black hole has evaporated. Because this effect changes the causal structure of space-time, it has crucial implications for black-hole models that have been missed in several older constructions, for instance in models based on bouncing black-hole interiors. Such models are ruled out by signature change even if their underlying space-times are made consistent using generalized covariance. The causal nature of signature change brings in a new internal consistency condition, given by the requirement of deterministic behavior at low curvature. Even a causally disconnected interior transition, opening back up into the former exterior as some kind of astrophysical white hole, is then ruled out. New versions consistent with both generalized covariance and low-curvature determinism are introduced here, showing a remarkable similarity with models developed in other approaches, such as the final-state proposal or the no-transition principle obtained from the gauge-gravity correspondence.

scholarly journals Loop quantum gravity, signature change, and the no-boundary proposal

2020 ◽  
Vol 102 (10) ◽  
Author(s):  
Martin Bojowald ◽  
Suddhasattwa Brahma
Keyword(s):  
Quantum Gravity ◽  
Loop Quantum Gravity ◽  
Signature Change

scholarly journals Review on hermiticity of the volume operators in Loop Quantum Gravity

2019 ◽  
Vol 51 (5) ◽  
Author(s):  
S. Ariwahjoedi ◽  
I. Husin ◽  
I. Sebastian ◽  
F. P. Zen
Keyword(s):  
Quantum Gravity ◽  
Loop Quantum Gravity
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