scholarly journals Causality and gravity

2021 ◽  
Vol 2021 (11) ◽  
Author(s):  
John F. Donoghue ◽  
Gabriel Menezes
Keyword(s):  
Field Theory ◽  
Quantum Gravity ◽  
Effective Field Theory ◽  
Causal Structure ◽  
Effective Field ◽  
Common Features ◽  
Quadratic Gravity

Abstract We show how uncertainty in the causal structure of field theory is essentially inevitable when one includes quantum gravity. This includes the fact that lightcones are ill-defined in such a theory. This effect is small in the effective field theory regime, where it is independent of the UV completion of the theory, but grows with energy and represents an unknown uncertainty for a generic UV completion. We include details of the causality uncertainty which arises in a particular UV completion, i.e. quadratic gravity. We describe how the mechanisms uncovered in the effective field theory treatment, and some of those in quadratic gravity, could be common features of quantum gravity.

scholarly journals Singularity Theorems in the Effective Field Theory for Quantum Gravity at Second Order in Curvature

Universe ◽  
2020 ◽  
Vol 6 (10) ◽  
pp. 171
Author(s):  
Folkert Kuipers ◽  
Xavier Calmet
Keyword(s):  
Field Theory ◽  
Quantum Gravity ◽  
Effective Field Theory ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Effective Field ◽  
Second Order ◽  
Jordan Frame ◽  
Singularity Theorems ◽  
Massive Spin

In this paper, we discuss singularity theorems in quantum gravity using effective field theory methods. To second order in curvature, the effective field theory contains two new degrees of freedom which have important implications for the derivation of these theorems: a massive spin-2 field and a massive spin-0 field. Using an explicit mapping of this theory from the Jordan frame to the Einstein frame, we show that the massive spin-2 field violates the null energy condition, while the massive spin-0 field satisfies the null energy condition, but may violate the strong energy condition. Due to this violation, classical singularity theorems are no longer applicable, indicating that singularities can be avoided, if the leading quantum corrections are taken into account.

scholarly journals Nonlocality in quantum gravity and the breakdown of effective field theory

2021 ◽  
Author(s):  
Nicolás Valdés-Meller
Keyword(s):  
Field Theory ◽  
Black Holes ◽  
Quantum Gravity ◽  
Effective Field Theory ◽  
Degrees Of Freedom ◽  
Effective Field ◽  
Length Scales ◽  
Effective Metric

We argue that quantum gravity is nonlocal, first by recalling well-known arguments that support this idea and then by focusing on a point not usually emphasized: that making a conventional effective field theory (EFT) for quantum gravity is particularly difficult, and perhaps impossible in principle. This inability to realize an EFT comes down to the fact that gravity itself sets length scales for a problem: when integrating out degrees of freedom above some cutoff, the effective metric one uses will be different, which will itself re-define the cutoff. We also point out that even if the previous problem is fixed, naïvely applying EFT in gravity can lead to problems — we give a particular example in the case of black holes.

scholarly journals Effective field theory of quantum gravity coupled to scalar electrodynamics

2016 ◽  
Vol 33 (9) ◽  
pp. 095008
Author(s):  
L Ibiapina Bevilaqua ◽  
A C Lehum ◽  
A J da Silva
Keyword(s):  
Field Theory ◽  
Quantum Gravity ◽  
Effective Field Theory ◽  
Effective Field

nflation from the Persepective of Quantum Gravity

2020 ◽  
Vol 29 (11) ◽  
pp. 26-30
Author(s):  
Seoktae KOH ◽  
Jinn-Ouk GONG ◽  
Min-Seok SEO
Keyword(s):  
Field Theory ◽  
Quantum Gravity ◽  
Effective Field Theory ◽  
Model Building ◽  
Quantum Fluctuations ◽  
De Sitter Space ◽  
Effective Field ◽  
De Sitter ◽  
Space Model

A brief review on inflation is given from the quantum gravity perspective. Using the effective field theory, we discuss quantum fluctuations and how they evolve into classical perturbations. We then list some limitations on de Sitter space model building and unresolved issues of inflation theory, together with persepectives.

scholarly journals SHAPE DYNAMICS AND EFFECTIVE FIELD THEORY

2013 ◽  
Vol 28 (13) ◽  
pp. 1330017 ◽  
Author(s):  
TIM A. KOSLOWSKI
Keyword(s):  
Field Theory ◽  
General Relativity ◽  
Quantum Gravity ◽  
Effective Field Theory ◽  
Conformal Geometry ◽  
Effective Field ◽  
Shape Dynamics ◽  
Weyl Invariance ◽  
Exact Renormalization Group ◽  
Canonical Quantum Gravity

Shape dynamics is a gauge theory based on spatial diffeomorphism- and Weyl-invariance which is locally indistinguishable from classical general relativity. If taken seriously, it suggests that the space–time geometry picture that underlies general relativity can be replaced by a picture based on spatial conformal geometry. This classically well-understood trading of gauge symmetries opens new conceptual avenues in many approaches to quantum gravity. This paper focusses on the general implications for quantum gravity and effective field theory and considers the application of the shape dynamics picture in the exact renormalization group approaches to gravity, loop- and polymer-quantization approaches to gravity and low energy effective field theories. Also, the interpretation of known results is discussed through the shape dynamics picture, particularly holographic renormalization and the problem of time in canonical quantum gravity.

scholarly journals Constraints on discrete global symmetries in quantum gravity

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Passant Ali ◽  
Astrid Eichhorn ◽  
Martin Pauly ◽  
Michael M. Scherer
Keyword(s):  
Field Theory ◽  
Quantum Gravity ◽  
Global Symmetries ◽  
Effective Field Theory ◽  
Effective Field ◽  
Fine Tuning ◽  
Theory Approach ◽  
Perturbative Regime

Abstract The question whether global symmetries can be realized in quantum-gravity-matter-systems has far-reaching phenomenological consequences. Here, we collect evidence that within an asymptotically safe context, discrete global symmetries of the form ℤn, n > 4, cannot be realized in a near-perturbative regime. In contrast, an effective-field-theory approach to quantum gravity might feature such symmetries, providing a mechanism to generate mass hierarchies in the infrared without the need for additional fine-tuning.

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