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Universe
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Quantum Field Theory in Curved Spacetime and Its Implications for...
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Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity, 2nd Edition

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: 15 November 2026 | Viewed by 3442

Special Issue Editors

Dr. Korumilli Sravan Kumar

E-Mail Website
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
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, 6201-001 Covilha, Portugal
Interests: cosmology; blackhole physics; quantum gravity; extensions to the standard model of particle physics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Following on from the humongous success of quantum field theory and general relativity (GR), the next big thing that has been puzzling generations of physicists is “quantum field theory in curved spacetime (QFTCS)”. The main objective of 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 uncovered striking questions regarding the well-known problems of unitarity and information loss in the contexts of de Sitter spacetime and Schwarzschild black holes. Although QFTCS has had its successes in predicting CMB correlations through cosmic inflation and Hawking radiation, it has nevertheless remained incomplete due to the lack of S-matrix construction and a unique choice of vacuum, a situation that entails many conceptual conundrums. Several resolutions to the problems of QFTCS have been proposed widely 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 explorations of how this framework portrays quantum field theory in curved spacetime, which dictates our understanding of early-universe cosmology and black hole physics. We also want to display various schemes for the quantization of fields in curved spacetime and investigations into how we can probe them through cosmological and astrophysical observations.

In a nutshell, the aim of this Special Issue is to pin down our understandings of the quantum mechanical nature of spacetime itself at fundamental scales. This Special Issue is dedicated to combining all of these scientific advances, highlighting further open questions on the subject. We welcome review articles as well as new research contributions as part of this Special Issue and we hope this Special Issue will be a significant driving force for further advancements in the field of QFTCS and quantum gravity.

Dr. Korumilli Sravan Kumar
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 250 words) can be sent to the Editorial Office for assessment.

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
  • black holes
  • cosmology

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Published Papers (4 papers)

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Research

13 pages, 569 KB  
Article
Hawking Atmosphere of Anti-de Sitter Black Holes
by A. F. Cardona and C. Molina
Universe 2026, 12(5), 141; https://doi.org/10.3390/universe12050141 - 9 May 2026
Viewed by 116
Abstract
This work investigates the semiclassical evolution of the Hawking atmosphere surrounding evaporating, spherically symmetric anti-de Sitter (adS) black holes. We model the evaporation process within a dynamical framework, treating the emission of Hawking radiation as a quantum tunneling process through the black-hole horizon. [...] Read more.
This work investigates the semiclassical evolution of the Hawking atmosphere surrounding evaporating, spherically symmetric anti-de Sitter (adS) black holes. We model the evaporation process within a dynamical framework, treating the emission of Hawking radiation as a quantum tunneling process through the black-hole horizon. Using the Parikh–Wilczek tunneling method, we incorporate backreaction effects, with the emission probability being linked to the resulting change in the Bekenstein–Hawking entropy of the black hole. This probability is then used to compute the time-dependent luminosity of the system, revealing significant deviations from ideal blackbody behavior, particularly for small adS black holes. For these objects, the luminosity does not increase with temperature due to strong mass variations during evaporation. To complement this microscopic approach, we compute the renormalized energy–momentum tensor for a quantum field propagating in the Vaidya-adS geometry modelling the evaporation process. Together, these approaches clarify the interplay between geometry, quantum fields, and thermodynamics in shaping the Hawking atmosphere and the evaporation dynamics of black holes in asymptotically adS spacetimes. Full article
(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity, 2nd Edition)
18 pages, 357 KB  
Article
Local Feynman Diagrammatics in Curved Spacetime: A Consistent LMC Framework
by Fridolin Weber
Universe 2026, 12(4), 111; https://doi.org/10.3390/universe12040111 - 10 Apr 2026
Viewed by 323
Abstract
We develop a general framework for quantum field theory in curved spacetime based on Local Minkowski Coordinates (LMC), which incorporates curvature effects into local Feynman diagrammatics. Gravitational influence enters through a curvature-dependent normalization function B(x), derived from covariant current [...] Read more.
We develop a general framework for quantum field theory in curved spacetime based on Local Minkowski Coordinates (LMC), which incorporates curvature effects into local Feynman diagrammatics. Gravitational influence enters through a curvature-dependent normalization function B(x), derived from covariant current conservation, and a gravitational phase S(x), obtained via the WKB approximation. These quantities enter through local phase accumulation and observer-dependent normalization of external states, without modifying globally conserved fluxes. As a first application, we analyze the local redshift normalization and phase structure of quantum amplitudes in the vicinity of a Schwarzschild black hole. Within their range of validity, the curvature-dependent factors B(x) and S(x) reproduce the expected gravitational redshift of field amplitudes in general relativity. When amplitudes are propagated to asymptotic infinity and evaluated in a standard global quantum state (such as the Unruh state), the resulting flux is consistent with the standard Hawking result. The framework refines the local WKB structure and clarifies the separation between local normalization effects and globally conserved fluxes. Full article
(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity, 2nd Edition)
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36 pages, 451 KB  
Article
The Thermodynamics of Transient Trapped Surfaces in the Geon Collapse
by Claes Cramer
Universe 2026, 12(4), 95; https://doi.org/10.3390/universe12040095 - 27 Mar 2026
Viewed by 874
Abstract
It is shown that transient trapped surfaces form in a class of emerging globally hyperbolic spacetimes, within punctured Planck-scale neighbourhoods of the geon supported on intersecting singular supports whose intersection forms a characteristic core in a non-strongly causal setting. These neighbourhoods shrink towards [...] Read more.
It is shown that transient trapped surfaces form in a class of emerging globally hyperbolic spacetimes, within punctured Planck-scale neighbourhoods of the geon supported on intersecting singular supports whose intersection forms a characteristic core in a non-strongly causal setting. These neighbourhoods shrink towards the intersecting singular support in the distributional geometry. In particular, the trapped surfaces occur near the characteristic limit corresponding to the unstable equilibrium of the self-gravitating geon. They act as an effective classical barrier for descriptions formulated purely within smooth differential geometry. The area of these trapped-surface configurations, computed on Planck-referenced neighbourhoods, is shown to tend to zero both in the asymptotically flat limit of the emerging spacetime and in the geon limit. Thus, transient trapped surfaces evaporate in the sense that their area vanishes as classical and asymptotically flat spacetime emerges within the quantum foam framework. A state-counting generating function for the transient trapped surfaces is constructed from the coherent-state density operator. This generating function maps microscopic occupation-number sectors to macroscopic data and thereby allows a definition of Boltzmann entropy (not to be confused with the von Neumann entropy, which is zero for any pure coherent state). Since the coherent state is constructed to implement the correspondence principle, expectation values of the relevant quantised observables reproduce their classical values. In particular, the expectation value of the bosonic occupation-number operator serves as a microstate-counting variable in the coherent sector. The generating function takes the form of an exponential of this expectation value, leading to an entropy–area relation consistent with the Hawking–Bekenstein scaling. Full article
(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity, 2nd Edition)
12 pages, 442 KB  
Article
Black-Hole Evaporation for Cosmological Observers
by Thiago de L. Campos, C. Molina and J. A. S. Lima
Universe 2025, 11(12), 394; https://doi.org/10.3390/universe11120394 - 30 Nov 2025
Viewed by 1144
Abstract
This work investigates the evaporation of black holes immersed in a de Sitter environment, using the Vaidya-de Sitter spacetime. The role of cosmological observers is highlighted in the development and Hayward thermodynamics for non-stationary geometries is employed in the description of the compact [...] Read more.
This work investigates the evaporation of black holes immersed in a de Sitter environment, using the Vaidya-de Sitter spacetime. The role of cosmological observers is highlighted in the development and Hayward thermodynamics for non-stationary geometries is employed in the description of the compact objects. The results of the proposed dynamical model are compared with the usual description based on stationary geometries, with specific results for primordial black holes (PBHs). The timescale of evaporation is shown to depend significantly on the choice of cosmological observer and can differ substantially from predictions based on stationary models at late times. Deviations are also shown with respect to the standard assertion that there is a fixed initial mass just below 1015g∼10−18M⊙ for the PBHs which are completing their evaporation process at the present epoch. Full article
(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity, 2nd Edition)
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