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Universe
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Cosmological Constant
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Cosmological Constant

A special issue of Universe (ISSN 2218-1997). This special issue belongs to the section "Cosmology".

Deadline for manuscript submissions: closed (31 December 2022) | Viewed by 10217

Special Issue Editors

Prof. Dr. Antonio Padilla

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Guest Editor
School of Physics & Astronomy for Astronomy, University Park, University of Nottingham, Nottingham NG7 2RD, UK
Interests: dark energy; dark matter; particle physics; gravity; cosmological constant problem
Special Issues, Collections and Topics in MDPI journals
Dr. Ippocratis Saltas

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Guest Editor
Institute of Physics of the Czech Academy of Sciences, Na Slovance 2, 182 21 Prague, Czech Republic
Interests: dark energy; gravity; cosmology and astrophysics
Dr. Adam R. Solomon

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Guest Editor
1. Department of Physics & Astronomy, McMaster University, Hamilton, ON L8S 4M1, Canada
2. Perimeter Institute for Theoretical Physics, 31 Caroline St. N, Waterloo, ON N2L 2Y5, Canada
Interests: cosmology; gravity; particle physics
Dr. Daniela Saadeh

E-Mail Website
Guest Editor
1. School of Physics and Astronomy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
2. Institute of Cosmology and Gravitation, University of Portsmouth, Portsmouth PO1 3FX, UK
Interests: cosmology and gravitation
Dr. David Stefanyszyn

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Guest Editor
Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Wilberforce Road, Cambridge CB3 0WA, UK
Interests: cosmology and particle physics
Dr. Katarina Markovic

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Guest Editor
Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
Interests: observational cosmology

Special Issue Information

Dear Colleagues,

The cosmological constant (CC) problem poses a major challenge for modern theoretical physics. In simple terms, it relates to our inability to reconcile the scale of the observed late-time acceleration of the universe to the natural scale of vacuum energy predicted by a fundamental theory. The problem is unique in that it relates a detailed understanding of microscopic physics to phenomenology on astrophysical and cosmological scales. Its resolution is expected to lead to a paradigm shift in our understanding of quantum field theory and gravity and reveal new physics beyond the current standard model of particles and forces.  

This Special Issue, led by early career researchers, aims to summarise the state of the art of current research on the theory and phenomenology of the CC problem and gathering contributions from experts in cosmology, astrophysics and quantum field theory. In particular, the issue provides an overview of theoretical attempts to attack the CC problem in a fundamental manner, as well as the phenomenological/observational hints that point to the need for new physics.

Prof. Dr. Antonio Padilla
Dr. Ippocratis Saltas
Dr. Adam R. Solomon
Dr. Daniela Saadeh
Dr. David Stefanyszyn
Dr. Katarina Markovic
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

  • cosmological constant problem
  • gravity
  • dark energy
  • large-scale structure and astrophysics
  • quantum field theory
  • string theory

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Published Papers (6 papers)

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Research

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31 pages, 387 KiB  
Article
Contemporary Philosophical Perspectives on the Cosmological Constant
by Adam Koberinski, Bridget Falck and Chris Smeenk
Universe 2023, 9(3), 134; https://doi.org/10.3390/universe9030134 - 5 Mar 2023
Cited by 2 | Viewed by 2015
Abstract
The (re)introduction of Λ into cosmology has spurred debates that touch on central questions in philosophy of science, as well as the foundations of general relativity and particle physics. We provide a systematic assessment of the often implicit philosophical assumptions guiding the methodology [...] Read more.
The (re)introduction of Λ into cosmology has spurred debates that touch on central questions in philosophy of science, as well as the foundations of general relativity and particle physics. We provide a systematic assessment of the often implicit philosophical assumptions guiding the methodology of precision cosmology in relation to dark energy. We start by briefly introducing a recent account of scientific progress in terms of risky and constrained lines of inquiry. This allows us to contrast aspects of Λ that make it relevantly different from other theoretical entities in science, such as its remoteness from direct observation or manipulability. We lay out a classification for possible ways to explain apparent accelerated expansion but conclude that these conceptually clear distinctions may blur heavily in practice. Finally, we consider the important role played in cosmology by critical tests of background assumptions, approximation techniques, and core principles, arguing that the weak anthropic principle fits into this category. We argue that some core typicality assumptions—such as the Copernican principle and the cosmological principle—are necessary though not provable, while others—such as the strong anthropic principle and appeals to naturalness or probability in the multiverse—are not similarly justifiable. Full article
(This article belongs to the Special Issue Cosmological Constant)

Review

Jump to: Research

32 pages, 1878 KiB  
Review
Modeling and Testing Screening Mechanisms in the Laboratory and in Space
by Valeri Vardanyan and Deaglan J. Bartlett
Universe 2023, 9(7), 340; https://doi.org/10.3390/universe9070340 - 20 Jul 2023
Cited by 5 | Viewed by 845
Abstract
The non-linear dynamics of scalar fields coupled to matter and gravity can lead to remarkable density-dependent screening effects. In this short review, we present the main classes of screening mechanisms, and discuss their tests in laboratory and astrophysical systems. We particularly focused on [...] Read more.
The non-linear dynamics of scalar fields coupled to matter and gravity can lead to remarkable density-dependent screening effects. In this short review, we present the main classes of screening mechanisms, and discuss their tests in laboratory and astrophysical systems. We particularly focused on reviewing numerical and technical aspects involved in modeling the non-linear dynamics of screening and on tests using laboratory experiments and astrophysical systems, such as stars, galaxies, and dark matter halos. Full article
(This article belongs to the Special Issue Cosmological Constant)
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69 pages, 5960 KiB  
Review
Cosmological Probes of Structure Growth and Tests of Gravity
by Jiamin Hou, Julian Bautista, Maria Berti, Carolina Cuesta-Lazaro, César Hernández-Aguayo, Tilman Tröster and Jinglan Zheng
Universe 2023, 9(7), 302; https://doi.org/10.3390/universe9070302 - 22 Jun 2023
Cited by 9 | Viewed by 1628
Abstract
The current standard cosmological model is constructed within the framework of general relativity with a cosmological constant Λ, which is often associated with dark energy, and phenomenologically explains the accelerated cosmic expansion. Understanding the nature of dark energy is one of the [...] Read more.
The current standard cosmological model is constructed within the framework of general relativity with a cosmological constant Λ, which is often associated with dark energy, and phenomenologically explains the accelerated cosmic expansion. Understanding the nature of dark energy is one of the most appealing questions in achieving a self-consistent physical model at cosmological scales. Modification of general relativity could potentially provide a more natural and physical solution to the accelerated expansion. The growth of the cosmic structure is sensitive in constraining gravity models. In this paper, we aim to provide a concise introductory review of modified gravity models from an observational point of view. We will discuss various mainstream cosmological observables, and their potential advantages and limitations as probes of gravity models. Full article
(This article belongs to the Special Issue Cosmological Constant)
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26 pages, 408 KiB  
Review
Unimodular Approaches to the Cosmological Constant Problem
by Pavel Jiroušek
Universe 2023, 9(3), 131; https://doi.org/10.3390/universe9030131 - 4 Mar 2023
Cited by 9 | Viewed by 985
Abstract
We review selected aspects of unimodular gravity and we discuss its viability as a solution of the old cosmological constant problem. In unimodular gravity, the cosmological constant is promoted to a global degree of freedom. We highlight the importance of correctly setting up [...] Read more.
We review selected aspects of unimodular gravity and we discuss its viability as a solution of the old cosmological constant problem. In unimodular gravity, the cosmological constant is promoted to a global degree of freedom. We highlight the importance of correctly setting up its initial data in order to achieve a resolution of the cosmological constant problem on a semi-classical level. We review recent path integral analysis of quantum aspects of unimodular gravity to note that the semi-classical findings carry over to the quantum level as well. We point out that a resolution of the problem inherently relies on a global constraint on the spacetime four-volume. This makes the theory closely related to the vacuum energy sequester, which operates in a similar way. We discuss possible avenues of extending unimodular gravity that preserve the resolution of the cosmological constant problem. Full article
(This article belongs to the Special Issue Cosmological Constant)
44 pages, 1867 KiB  
Review
Modified Gravity Approaches to the Cosmological Constant Problem
by Foundational Aspects of Dark Energy (FADE) Collaboration, Heliudson Bernardo, Benjamin Bose, Guilherme Franzmann, Steffen Hagstotz, Yutong He, Aliki Litsa and Florian Niedermann
Universe 2023, 9(2), 63; https://doi.org/10.3390/universe9020063 - 20 Jan 2023
Cited by 6 | Viewed by 1705
Abstract
The cosmological constant and its phenomenology remain among the greatest puzzles in theoretical physics. We review how modifications of Einstein’s general relativity could alleviate the different problems associated with it that result from the interplay of classical gravity and quantum field theory. We [...] Read more.
The cosmological constant and its phenomenology remain among the greatest puzzles in theoretical physics. We review how modifications of Einstein’s general relativity could alleviate the different problems associated with it that result from the interplay of classical gravity and quantum field theory. We introduce a modern and concise language to describe the problems associated with its phenomenology, and inspect no-go theorems and their loopholes to motivate the approaches discussed here. Constrained gravity approaches exploit minimal departures from general relativity; massive gravity introduces mass to the graviton; Horndeski theories lead to the breaking of translational invariance of the vacuum; and models with extra dimensions change the symmetries of the vacuum. We also review screening mechanisms that have to be present in some of these theories if they aim to recover the success of general relativity on small scales as well. Finally, we summarize the statuses of these models in their attempts to solve the different cosmological constant problems while being able to account for current astrophysical and cosmological observations. Full article
(This article belongs to the Special Issue Cosmological Constant)
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37 pages, 497 KiB  
Review
Particles of a de Sitter Universe
by Gizem Şengör
Universe 2023, 9(2), 59; https://doi.org/10.3390/universe9020059 - 17 Jan 2023
Cited by 6 | Viewed by 1319
Abstract
The de Sitter spacetime is a maximally symmetric spacetime. It is one of the vacuum solutions to Einstein equations with a cosmological constant. It is the solution with a positive cosmological constant and describes a universe undergoing accelerated expansion. Among the possible signs [...] Read more.
The de Sitter spacetime is a maximally symmetric spacetime. It is one of the vacuum solutions to Einstein equations with a cosmological constant. It is the solution with a positive cosmological constant and describes a universe undergoing accelerated expansion. Among the possible signs for a cosmological constant, this solution is relevant for primordial and late-time cosmology. In the case of a zero cosmological constant, studies on the representations of its isometry group have led to a broader understanding of particle physics. The isometry group of d+1-dimensional de Sitter is the group SO(d+1,1), whose representations are well known. Given this insight, what can we learn about the elementary degrees of freedom in a four dimensional de Sitter universe by exploring how the unitary irreducible representations of SO(4,1) present themselves in cosmological setups? This article aims to summarize recent advances along this line that benefit towards a broader understanding of quantum field theory and holography at different signs of the cosmological constant. Particular focus is given to the manifestation of SO(4,1) representations at the late-time boundary of de Sitter. The discussion is concluded by pointing towards future questions at the late-time boundary and the static patch with a focus on the representations. Full article
(This article belongs to the Special Issue Cosmological Constant)
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