scholarly journals How to hide a cosmological constant

2019 ◽  
Vol 28 (14) ◽  
pp. 1943004 ◽  
Author(s):  
Steven Carlip
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Cosmological Constant ◽  
Planck Scale ◽  
Quantum Field ◽  
Vacuum Fluctuations ◽  
And Topology ◽  
Spacetime Foam

Naive calculations in quantum field theory suggest that vacuum fluctuations should induce an enormous cosmological constant. What if these estimates are right? I argue that even a huge cosmological constant might be hidden in Planck-scale fluctuations of geometry and topology — what Wheeler called “spacetime foam” — while remaining virtually invisible macroscopically.

scholarly journals NEGATIVE ENERGY DENSITIES IN QUANTUM FIELD THEORY

2010 ◽  
Vol 25 (11) ◽  
pp. 2355-2363 ◽  
Author(s):  
L. H. FORD
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Energy Density ◽  
Negative Energy ◽  
Mean Value ◽  
Quantum Field ◽  
Two Dimensional ◽  
Vacuum Fluctuations ◽  
Negative Energy Density ◽  
Dimensional Spacetime

Quantum field theory allows for the suppression of vacuum fluctuations, leading to sub-vacuum phenomena. One of these is the appearance of local negative energy density. Selected aspects of negative energy will be reviewed, including the quantum inequalities which limit its magnitude and duration. However, these inequalities allow the possibility that negative energy and related effects might be observable. Some recent proposals for experiments to search for sub-vacuum phenomena will be discussed. Fluctuations of the energy density around its mean value will also be considered, and some recent results on a probability distribution for the energy density in two dimensional spacetime are summarized.

scholarly journals Null Wave Front and Ryu–Takayanagi Surface

Entropy ◽  
2020 ◽  
Vol 22 (11) ◽  
pp. 1297
Author(s):  
Jun Tsujimura ◽  
Yasusada Nambu
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Cosmological Constant ◽  
Minimal Surface ◽  
Wave Front ◽  
Entanglement Entropy ◽  
Necessary Condition ◽  
Quantum Field ◽  
Wave Fronts ◽  
Sufficient And Necessary Condition

The Ryu–Takayanagi formula provides the entanglement entropy of quantum field theory as an area of the minimal surface (Ryu–Takayanagi surface) in a corresponding gravity theory. There are some attempts to understand the formula as a flow rather than as a surface. In this paper, we consider null rays emitted from the AdS boundary and construct a flow representing the causal holographic information. We present a sufficient and necessary condition that the causal information surface coincides with Ryu–Takayanagi surface. In particular, we show that, in spherical symmetric static spacetimes with a negative cosmological constant, wave fronts of null geodesics from a point on the AdS boundary become extremal surfaces and therefore they can be regarded as the Ryu–Takayanagi surfaces. In addition, from the viewpoint of flow, we propose a wave optical formula to calculate the causal holographic information.

Quantization and topology: SL(2,R)-de Sitter invariant fields in two dimensions

2020 ◽  
Vol 35 (02n03) ◽  
pp. 2040018
Author(s):  
Henri Epstein ◽  
Ugo Moschella
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Two Dimensions ◽  
Quantum Field ◽  
Two Dimensional ◽  
De Sitter ◽  
Cosmological Background ◽  
Local Commutativity ◽  
And Topology ◽  
The Many

We explore the interplay between quantization, local commutativity and the analyticity properties of the two-point functions of a quantum field in a non trivial topological cosmological background in the example of the two-dimensional de Sitter manifold and its double covering. The global topological differences make the many of the well-known features of de Sitter quantum field theory disappear. In particular there is nothing like a Bunch-Davies vacuum and there are no [Formula: see text]-invariant fields whose mass is less than 1/2.

scholarly journals On the quantum field theory of the gravitational interactions

2018 ◽  
Author(s):  
Damiano Anselmi
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Cosmological Constant ◽  
Gauge Coupling ◽  
Cosmological Term ◽  
Power Counting ◽  
Quantum Field ◽  
Higher Derivative ◽  
S Matrix ◽  
Local Quantum

We study the main options for a unitary and renormalizable, local quantum field theory of the gravitational interactions. The first model is a Lee-Wick superrenormalizable higher-derivative gravity, formulated as a nonanalytically Wick rotated Euclidean theory. We show that, under certain conditions, the $S$ matrix is unitary when the cosmological constant vanishes. The model is the simplest of its class. However, infinitely many similar options are allowed, which raises the issue of uniqueness. To deal with this problem, we propose a new quantization prescription, by doubling the unphysical poles of the higher-derivative propagators and turning them into Lee-Wick poles. The Lagrangian of the simplest theory of quantum gravity based on this idea is the linear combination of $R$, $R_{\mu \nu}R^{\mu \nu }$, $R^{2}$ and the cosmological term. Only the graviton propagates in the cutting equations and, when the cosmological constant vanishes, the $S$ matrix is unitary. The theory satisfies the locality of counterterms and is renormalizable by power counting. It is unique in the sense that it is the only one with a dimensionless gauge coupling.

scholarly journals Infrared surprises in the de Sitter universe

2016 ◽  
Vol 25 (09) ◽  
pp. 1641020 ◽  
Author(s):  
Ugo Moschella
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Cosmological Constant ◽  
Quantum Field ◽  
De Sitter ◽  
Sitter Universe ◽  
De Sitter Universe

We describe a few unexpected features of de Sitter quantum field theory (QFT) that have no Minkowskian counterparts. These phenomena show that even when the cosmological constant is tiny a Minkowskian way of fast thinking about de Sitter can lead to mistakes and that de Sitter QFT is essentially different from standard relativistic (Minkowskian) QFT.

Final remarks on Part II

2021 ◽  
pp. 503-503
Author(s):  
Iosif L. Buchbinder ◽  
Ilya L. Shapiro
Keyword(s):  
Field Theory ◽  
Quantum Field Theory ◽  
Quantum Gravity ◽  
Cosmological Constant ◽  
General Situation ◽  
Quantum Field ◽  
Gravitational Effects ◽  
Higher Derivative ◽  
Perfect Model ◽  
Perturbative Quantum

This brief concluding chapter summarizes the general situation in semiclassical theory and quantum gravity. Even in the framework of the usual perturbative quantum field theory, there are several approaches leading to theoretically satisfactory models of quantum gravitational effects, starting from quantum field theory in curved spacetime. Here, the expression “satisfactory” does not mean perfectness, as there is no theoretically perfect model of quantum gravity. The chapter then goes on to review the main unsolved problems of quantum gravity, such as higher-derivative ghosts and instabilities and the cosmological constant problem. It concludes with the hope that the basic aspects of the models presented in this book will be useful for anyone who intends to start working in this fascinating area.

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