scholarly journals Influence of the measure on simplicial quantum gravity in four dimensions

1992 ◽  
Vol 69 (5) ◽  
pp. 713-716 ◽  
Author(s):  
Wolfgang Beirl ◽  
Erwin Gerstenmayer ◽  
Harold Markum
Keyword(s):  
Quantum Gravity ◽  
Four Dimensions

scholarly journals LARGE QUANTUM GRAVITY EFFECTS: CYLINDRICAL WAVES IN FOUR DIMENSIONS

2000 ◽  
Vol 09 (06) ◽  
pp. 669-686 ◽  
Author(s):  
MARÍA E. ANGULO ◽  
GUILLERMO A. MENA MARUGÁN
Keyword(s):  
Quantum Gravity ◽  
Symmetry Axis ◽  
Point Of View ◽  
Three Dimensions ◽  
Asymptotic Region ◽  
Four Dimensions ◽  
Cylindrical Waves ◽  
Significant Difference ◽  
Gravity Effects ◽  
Linearly Polarized

Linearly polarized cylindrical waves in four-dimensional vacuum gravity are mathematically equivalent to rotationally symmetric gravity coupled to a Maxwell (or Klein–Gordon) field in three dimensions. The quantization of this latter system was performed by Ashtekar and Pierri in a recent work. Employing that quantization, we obtain here a complete quantum theory which describes the four-dimensional geometry of the Einstein–Rosen waves. In particular, we construct regularized operators to represent the metric. It is shown that the results achieved by Ashtekar about the existence of important quantum gravity effects in the Einstein–Maxwell system at large distances from the symmetry axis continue to be valid from a four-dimensional point of view. The only significant difference is that, in order to admit an approximate classical description in the asymptotic region, states that are coherent in the Maxwell field need not contain a large number of photons anymore. We also analyze the metric fluctuations on the symmetry axis and argue that they are generally relevant for all of the coherent states.

Exploration of simplicial quantum gravity in four dimensions

1992 ◽  
Vol 26 ◽  
pp. 575-577 ◽  
Author(s):  
Wolfgang Beirl ◽  
Erwin Gersienmayer ◽  
Harald Markum
Keyword(s):  
Quantum Gravity ◽  
Four Dimensions

scholarly journals Quantum corrections in 4d N = 1 infinite distance limits and the weak gravity conjecture

2021 ◽  
Vol 2021 (3) ◽  
Author(s):  
Daniel Klaewer ◽  
Seung-Joo Lee ◽  
Timo Weigand ◽  
Max Wiesner
Keyword(s):  
Quantum Gravity ◽  
Weak Coupling Limit ◽  
Quantum Corrections ◽  
Classical Level ◽  
Four Dimensions ◽  
Weakly Coupled ◽  
The Masses ◽  
Perturbative Corrections ◽  
Weak Gravity ◽  
Kaluza Klein

Abstract We study quantum corrections in four-dimensional theories with N = 1 supersymmetry in the context of Quantum Gravity Conjectures. According to the Emergent String Conjecture, infinite distance limits in quantum gravity either lead to decompactification of the theory or result in a weakly coupled string theory. We verify this conjecture in the framework of N = 1 supersymmetric F-theory compactifications to four dimensions including perturbative α′ as well as non-perturbative corrections. After proving uniqueness of the emergent critical string at the classical level, we show that quantum corrections obstruct precisely those limits in which the scale of the emergent critical string would lie parametrically below the Kaluza-Klein scale. Limits in which the tension of the asymptotically tensionless string sits at the Kaluza-Klein scale, by contrast, are not obstructed.In the second part of the paper we study the effect of quantum corrections for the Weak Gravity Conjecture away from the strict weak coupling limit. We propose that gauge threshold corrections and mass renormalisation effects modify the super-extremality bound in four dimensions. For the infinite distance limits in F-theory the classical super-extremality bound is generically satisfied by a sublattice of states in the tower of excitations of an emergent heterotic string. By matching the F-theory α′-corrections to gauge threshold corrections of the dual heterotic theory we predict how the masses of this tower must be renormalised in order for the Weak Gravity Conjecture to hold at the quantum level.

scholarly journals Fakeons, quantum gravity and the correspondence principle

2019 ◽  
Author(s):  
Damiano Anselmi
Keyword(s):  
Quantum Gravity ◽  
Correspondence Principle ◽  
Special Role ◽  
Quantum Field Theories ◽  
Quantum Field ◽  
Classical Action ◽  
Four Dimensions ◽  
The Standard Model ◽  
Matter Sector

The correspondence principle made of unitarity, locality and renormalizability has been very successful in quantum field theory. Among the other things, it helped us build the standard model. However, it also showed important limitations. For example, it failed to restrict the gauge group and the matter sector in a powerful way. After discussing its effectiveness, we upgrade it to make room for quantum gravity. The unitarity assumption is better understood, since it allows for the presence of physical particles as well as fake particles (fakeons). The locality assumption is applied to an interim classical action, since the true classical action is nonlocal and emerges from the quantization and a later process of classicization. The renormalizability assumption is refined to single out the special role of the gauge couplings. We show that the upgraded principle leads to an essentially unique theory of quantum gravity. In particular, in four dimensions, a fakeon of spin 2, together with a scalar field, is able to make the theory renormalizable while preserving unitarity. We offer an overview of quantum field theories of particles and fakeons in various dimensions, with and without gravity.

scholarly journals Cosmological Constant from Condensation of Defect Excitations

Universe ◽  
2018 ◽  
Vol 4 (7) ◽  
pp. 81 ◽  
Author(s):  
Bianca Dittrich
Keyword(s):  
Hilbert Space ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
Quantum Cosmology ◽  
Condensed Matter ◽  
Three Dimensional ◽  
Class Constraint ◽  
Four Dimensions ◽  
Dimensional Gravity ◽  
Constraint Algebra

A key challenge for many quantum gravity approaches is to construct states that describe smooth geometries on large scales. Here we define a family of (2+1)-dimensional quantum gravity states which arise from curvature excitations concentrated at point like defects and describe homogeneously curved geometries on large scales. These states represent therefore vacua for three-dimensional gravity with different values of the cosmological constant. They can be described by an anomaly-free first class constraint algebra quantized on one and the same Hilbert space for different values of the cosmological constant. A similar construction is possible in four dimensions, in this case the curvature is concentrated along string-like defects and the states are vacua of the Crane-Yetter model. We will sketch applications for quantum cosmology and condensed matter.

scholarly journals Higher derivative quantum gravity near four dimensions

2005 ◽  
Vol 35 (4b) ◽  
pp. 1099-1103 ◽  
Author(s):  
Guilherme de Berredo-Peixoto ◽  
Ilya L. Shapiro
Keyword(s):  
Quantum Gravity ◽  
Four Dimensions ◽  
Higher Derivative
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