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Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity

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A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Foundations of Quantum Mechanics and Quantum Gravity".

Deadline for manuscript submissions: 22 August 2024 | Viewed by 6955

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Special Issue Editors

Dr. Korumilli Sravan Kumar

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Guest Editor

Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3DE, UK
Interests: theoretical cosmology; blackhole physics; quantum gravity; modified gravity; string theory; beyond the standard model of particle physics

Prof. Dr. Joao Marto

E-Mail Website
Guest Editor

Departamento de Física e Centro de Matemática e Aplicações, Universidade da Beira Interior, Rua Marquês D’Ávila e Bolama, 6200-001 Covilhã, Portugal
Interests: cosmology; blackhole physics; quantum gravity; extensions to the standard model of particle physics

Special Issue Information

Dear Colleagues,

After the colossal success of the quantum field theory and general relativity (GR), the next big thing, having puzzled generations of physicists, is the “quantum field theory in curved spacetime (QFTCS)”. The main objective of the QFTCS is to understand how quantum fields behave when gravity is involved and how spacetime fluctuations can be quantum mechanical in nature. This endeavor has, thus far, uncovered striking questions related to the well-known problems of unitarity and information loss in the contexts of de Sitter’s spacetime and Schwarzschild’s black hole. Although the QFTCS has had its success in predicting CMB correlations through cosmic inflation and Hawking radiation, it has, nevertheless, remained incomplete due to the lack of an S-matrix construction and a unique choice of vacuum, a situation that entails many conceptual conundrums. Several resolutions to QFTCS problems have been widely proposed in the literature, especially in the context of various quantum gravity frameworks and effective field theories. We intend to bring together various attempts to quantize gravity and how their framework portrays the quantum field theory in curved spacetime, dictating our understanding of early universe cosmology and blackhole physics. We also wish to display various schemes for the quantization of fields in curved spacetime and how we could probe them through cosmological and astrophysical observations.

In a nutshell, the aim of this Special Issue is to resolve our understanding of the quantum mechanical nature of spacetime itself at a fundamental scale, and is also dedicated to combining all scientific progress, highlighting further open questions in the subject. We welcome review articles as well as novel research contributions as part of this Special Issue. We hope to receive significant contributions, making this Special Issue a significant driving force for further advancements in the field of the QFTCS and quantum gravity.

Sincerely,

Dr. Korumilli Sravan Kumar
Prof. Dr. Joao Marto
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Universe is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

quantum field theory in curved spacetime
quantum gravity
blackholes
cosmology

Published Papers (6 papers)

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Research

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25 pages, 622 KiB

Open AccessArticle

On Minimal Entanglement Wedge Cross Section for Holographic Entanglement Negativity

by Jaydeep Kumar Basak, Vinay Malvimat, Himanshu Parihar, Boudhayan Paul and Gautam Sengupta

Universe 2024, 10(3), 125; https://doi.org/10.3390/universe10030125 - 05 Mar 2024

Cited by 32 | Viewed by 789

Abstract

We demonstrate the equivalence of two different conjectures in the literature for the holographic entanglement negativity in AdS₃/CFT₂, modulo certain constants. These proposals involve certain algebraic sums of bulk geodesics homologous to specific combinations of subsystems, and the entanglement wedge cross section (EWCS) backreacted by a cosmic brane for the conical defect geometry in the bulk gravitational path integral. It is observed that the former conjectures reproduce the field theory replica technique results in the large central charge limit whereas the latter involves constants related to the Markov gap. In this context, we establish an alternative construction for the EWCS of a single interval in a CFT₂ at a finite temperature to resolve an issue for the latter proposal involving thermal entropy elimination for holographic entanglement negativity. Our construction for the EWCS correctly reproduces the corresponding field theory results modulo the Markov gap constant in the large central charge limit. Full article

(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity)

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18 pages, 432 KiB

Open AccessArticle

Vacuum Energy, the Casimir Effect, and Newton’s Non-Constant

by Benjamin Koch, Christian Käding, Mario Pitschmann and René I. P. Sedmik

Universe 2023, 9(11), 476; https://doi.org/10.3390/universe9110476 - 08 Nov 2023

Viewed by 1161

Abstract

The idea of quantum mechanical vacuum energy contributing to the cosmological vacuum energy density is not new. However, despite the persisting cosmological constant problem, few investigations have focused on this subject. We explore the possibility that the quantum vacuum energy density contributes to [...] Read more.

Λ

and Newton’s constant G. This hypothesis has several important consequences, ranging from quantum scale-dependence to the hypothetical prospect of novel experimental insight concerning the quantum origin of cosmological energy density. Full article

(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity)

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29 pages, 20294 KiB

Open AccessArticle

Quantum Black Holes in Conformal Dilaton–Higgs Gravity on Warped Spacetimes

by Reinoud Jan Slagter

Universe 2023, 9(9), 383; https://doi.org/10.3390/universe9090383 - 26 Aug 2023

Viewed by 1174

Abstract

A promising method for understanding the geometric properties of a spacetime in the vicinity of the horizon of a Kerr-like black hole can be developed by applying the antipodal boundary condition on the two opposite regions in the extended Penrose diagram. By considering a conformally invariant Lagrangian on a Randall–Sundrum warped five-dimensional spacetime, an exact vacuum solution is found, which can be interpreted as an instanton solution on the Riemannian counterpart spacetime,

R_{+}^{2} \times R^{1} \times S^{1}

, where

R_{+}^{2}

is conformally flat. The antipodal identification, which comes with a CPT inversion, is par excellence, suitable when quantum mechanical effects, such as the evaporation of a black hole by Hawking radiation, are studied. Moreover, the black hole paradoxes could be solved. By applying the non-orientable Klein surface, embedded in

R^{4}

, there is no need for instantaneous transport of information. Further, the gravitons become “hard” in the bulk, which means that the gravitational backreaction on the brane can be treated without the need for a firewall. By splitting the metric in a product

ω^{2} {\tilde{g}}_{μ ν}

, where

ω

represents a dilaton field and

{\tilde{g}}_{μ ν}

the conformally flat “un-physical” spacetime, one can better construct an effective Lagrangian in a quantum mechanical setting when one approaches the small-scale area. When a scalar field is included in the Lagrangian, a numerical solution is presented, where the interaction between

ω

and

Φ

is manifest. An estimate of the extra dimension could be obtained by measuring the elapsed traversal time of the Hawking particles on the Klein surface in the extra dimension. Close to the Planck scale, both

ω

and

Φ

can be treated as ordinary quantum fields. From the dilaton field equation, we obtain a mass term for the potential term in the Lagrangian, dependent on the size of the extra dimension. Full article

(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity)

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18 pages, 409 KiB

Open AccessArticle

Newtonian Cosmology and Evolution of κ-Deformed Universe

by E. Harikumar, Harsha Sreekumar and Suman Kumar Panja

Universe 2023, 9(7), 343; https://doi.org/10.3390/universe9070343 - 24 Jul 2023

Cited by 2 | Viewed by 711

Abstract

Considering space-time to be non-commutative, we study the evolution of the universe employing the approach of Newtonian cosmology. Generalizing the conservation of energy and the first law of thermodynamics to

κ

-deformed space-time, we derive the modified Friedmann equations, valid up to the [...] Read more.

κ

-deformed space-time, we derive the modified Friedmann equations, valid up to the first order, in the deformation parameter. Analyzing these deformed equations, we derive the time evolution of the scale factor in cases of radiation-dominated, matter-dominated, and vacuum (energy)-dominated universes. We show that the rate of change of the scale factor in all three situations is modified by the non-commutativity of space-time, and this rate depends on the sign of the deformation parameter, indicating a possible explanation for the observed Hubble tension. We undertake this investigation for two different realizations of non-commutative space-time coordinates. In both cases, we also argue for the existence of bounce in the evolution of the universe. Full article

(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity)

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16 pages, 512 KiB

Open AccessArticle

Fermionic Greybody Factors in Schwarzschild Acoustic Black Holes

by Sara Kanzi and İzzet Sakallı

Universe 2023, 9(2), 108; https://doi.org/10.3390/universe9020108 - 19 Feb 2023

Cited by 1 | Viewed by 1032

Abstract

In Schwarzschild acoustic black hole (SABH) spacetime, we investigate the wave dynamics for the fermions. To this end, we first take into account the Dirac equation in the SABH by employing a null tetrad in the Newman–Penrose (NP) formalism. Then, we consider the Dirac and Rarita–Schwinger equations, respectively. The field equations are reduced to sets of radial and angular equations. By using the analytical solution of the angular equation set, we decouple the radial wave equations and obtain the one-dimensional Schrödinger-like wave equations with their effective potentials. The obtained effective potentials are graphically depicted and analyzed. Finally, we investigate the fermionic greybody factors (GFs) radiated by the SABH spacetime. A thorough investigation is conducted into how the acoustic tuning parameter affects the GFs of the SABH spacetime. Both the semi-analytic WKB method and bounds for the GFs are used to produce the results, which are shown graphically and discussed. Full article

(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity)

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Review

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16 pages, 347 KiB

Open AccessReview

Quantum Imprints on CMBR

by Shreya Banerjee

Universe 2023, 9(9), 405; https://doi.org/10.3390/universe9090405 - 04 Sep 2023

Viewed by 906

Abstract

Quantum cosmology aims to develop a quantum theory of the universe, attempting to answer open questions of physical cosmology, mainly related to the early epochs of the universe. Such a theory aims to unite relativity theory and quantum theory. Here, the whole universe is treated as a quantum mechanical system and is described by a wave function rather than by a classical spacetime. In this review, I shall describe the mathematical structure and primary formulations that form the backbone of quantum cosmology. We know that over a period of time, several approaches were developed to form a quantum theory of gravity. However, in order to decide which approach is the best, we need testable predictions, effects that can be observed in cosmic microwave background radiation (CMBR). I shall discuss the methodologies for generating quantum gravitational corrections to inflationary background leading to testable predictions. Another aspect of finding quantum imprints on CMBR results through the application of resolution of the ‘quantum measurement problem’ to early universe physics. In this article, I shall also discuss two such promising models explaining the classicalization of inflationary perturbation and are capable of leaving distinct observational imprints on the observables. Full article

(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity)

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