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Latest Developments in the Quest for the Unification of Cosmic...
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Latest Developments in the Quest for the Unification of Cosmic Inflation and Dark Energy

A special issue of Galaxies (ISSN 2075-4434).

Deadline for manuscript submissions: closed (1 January 2022) | Viewed by 16267

Special Issue Editor

Dr. Konstantinos Dimopoulos

E-Mail Website
Guest Editor
Physics Department, Lancaster University, Lancaster LA1 4YB, UK
Interests: cosmic inflation; dark energy; primordial magnetic fields

Special Issue Information

Dear Colleagues,

This Special Issue will address the latest developments in the attempt to unify cosmic inflation and dark energy in the Universe.

Dark energy holds the key to the origin and fate of our Universe. When dominant, dark energy forces the expansion of the Universe to accelerate. Observations confirm that accelerated expansion just after the Big Bang explosion (cosmic inflation) set the stage for the Universe’s history, but it is also occurring today. Unifying primordial inflation and current dark energy allows for economic treatment in a common theoretical framework, directly linked with particle physics, constrained by observations of both inflation and late dark energy. Recent developments in the field have enabled this connection to be investigated in novel ways. Because dark energy can be accounted for by a potentially dominated scalar field called quintessence, unifying models have been called quintessential inflation.

Original efforts to construct quintessential inflation found the task daunting. Recent developments, however, offer new ways to efficiently deal with the challenges of unifying inflation with late dark energy. Prominent examples of such new developments in the theory involve the effect of kinetic poles in the scalar potential, direct non-minimal couplings of the scalar field to gravity, so-called disformal couplings or multi-field approaches with non-trivial geometry in configuration space, incorporation of gauge fields in model building and so on. Most such setups are yet to be utilized in a unified explanation of inflation and late dark energy. This effort is underpinned by the reduction in popularity of the concordance model ΛCDM, due to the “swampland conjectures”, as an explanation of late dark energy. Moreover, quintessential inflation may generate a spike in primordial gravitational waves (unlike in usual inflation), soon to be observable by LIGO and/or LISA.

This Special Issue will utilize the latest developments in particle theory to construct and analyze detailed models that address the requirements of early and late acceleration in the Universe expansion in a unified manner. The latest observations will also provide valuable insights into the underlying theory. Moreover, the proposed models will put forward concrete predictions to be put to the observational test but also shed light on the origin and ultimate fate of the Universe.

Dr. Konstantinos Dimopoulos
Guest Editor

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 papers will be 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. Galaxies is an international peer-reviewed open access quarterly 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

  • cosmic inflation
  • dark energy
  • quintessence
  • cosmology

Published Papers (6 papers)

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Research

Jump to: Review

14 pages, 460 KiB  
Article
Modelling Quintessential Inflation in Palatini-Modified Gravity
by Konstantinos Dimopoulos, Alexandros Karam, Samuel Sánchez López and Eemeli Tomberg
Galaxies 2022, 10(2), 57; https://doi.org/10.3390/galaxies10020057 - 5 Apr 2022
Cited by 11 | Viewed by 2093
Abstract
We study a model of quintessential inflation constructed in R2-modified gravity with a non-minimally coupled scalar field, in the Palatini formalism. Our non-minimal inflaton field is characterised by a simple exponential potential. We find that successful quintessential inflation can be achieved [...] Read more.
We study a model of quintessential inflation constructed in R2-modified gravity with a non-minimally coupled scalar field, in the Palatini formalism. Our non-minimal inflaton field is characterised by a simple exponential potential. We find that successful quintessential inflation can be achieved with no fine-tuning of the model parameters. Predictions of the characteristics of dark energy will be tested by observations in the near future, while contrasting with existing observations provides insights on the modified gravity background, such as the value of the non-minimal coupling and its running. Full article
(This article belongs to the Special Issue Latest Developments in the Quest for the Unification of Cosmic Inflation and Dark Energy)
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36 pages, 1683 KiB  
Article
What Is Needed of a Scalar Field If It Is to Unify Inflation and Late Time Acceleration?
by Nur Jaman and Mohammad Sami
Galaxies 2022, 10(2), 51; https://doi.org/10.3390/galaxies10020051 - 23 Mar 2022
Cited by 13 | Viewed by 2946
Abstract
Quintessential inflation refers to scenarios in which a single scalar field is used to describe inflation and late time acceleration. This review is dedicated to the framework of quintessential inflation, with a focus on the building blocks of formalism. Consistent unification of inflation [...] Read more.
Quintessential inflation refers to scenarios in which a single scalar field is used to describe inflation and late time acceleration. This review is dedicated to the framework of quintessential inflation, with a focus on the building blocks of formalism. Consistent unification of inflation and late time acceleration using a single scalar field asks for a shallow field potential initially followed by steep behaviour thereafter and shallow again around the present epoch. The requirement of non-interference of the scalar field with thermal history dictates the steep nature of potential in the post-inflationary era, with a further restriction that late time physics be independent of initial conditions. We describe, in detail, the scaling and asymptotic scaling solutions and the mechanism of exit from the scaling regime to late time acceleration. The review includes a fresh look at scaling solutions that are central to the theme of unification of inflation and late time acceleration. As for the exit mechanism, special attention is paid to the coupling of massive neutrino matter to the scalar field, which builds up dynamically and can give rise to late time acceleration. We present a detailed analytical treatment of scalar field dynamics in the presence of coupling. We briefly discuss the distinguishing feature of quintessential inflation, namely the blue spectrum of gravity waves produced during the transition from inflation to the kinetic regime. Full article
(This article belongs to the Special Issue Latest Developments in the Quest for the Unification of Cosmic Inflation and Dark Energy)
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19 pages, 564 KiB  
Article
The Quantum Gravity Connection between Inflation and Quintessence
by Christof Wetterich
Galaxies 2022, 10(2), 50; https://doi.org/10.3390/galaxies10020050 - 17 Mar 2022
Cited by 12 | Viewed by 2186
Abstract
Inflation and quintessence can both be described by a single scalar field. The cosmic time evolution of this cosmon field realizes a crossover from the region of an ultraviolet fixed point in the infinite past to an infrared fixed point in the infinite [...] Read more.
Inflation and quintessence can both be described by a single scalar field. The cosmic time evolution of this cosmon field realizes a crossover from the region of an ultraviolet fixed point in the infinite past to an infrared fixed point in the infinite future. This amounts to a transition from early inflation to late dynamical dark energy, with intermediate radiation and matter domination. The scaling solution of the renormalization flow in quantum gravity connects the two fixed points. It provides for the essential characteristics of the scalar potential needed for the crossover cosmology and solves the cosmological constant problem dynamically. The quantum scale symmetry at the infrared fixed point protects the tiny mass of the cosmon and suppresses the cosmon coupling to atoms without the need of a non-linear screening mechanism, thereby explaining apparent issues of fine tuning. For a given content of particles, the scaling solution of quantum gravity is a predictive framework for the properties of inflation and dynamical dark energy. Full article
(This article belongs to the Special Issue Latest Developments in the Quest for the Unification of Cosmic Inflation and Dark Energy)
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35 pages, 1046 KiB  
Article
Reheating in Runaway Inflation Models via the Evaporation of Mini Primordial Black Holes
by Ioannis Dalianis and George P. Kodaxis
Galaxies 2022, 10(1), 31; https://doi.org/10.3390/galaxies10010031 - 10 Feb 2022
Cited by 12 | Viewed by 2500
Abstract
We investigate the cosmology of mini Primordial Black Holes (PBHs) produced by large density perturbations that collapse during a stiff fluid domination phase. Such a phase can be realized by a runaway-inflaton model that crosses an inflection point or a sharp feature at [...] Read more.
We investigate the cosmology of mini Primordial Black Holes (PBHs) produced by large density perturbations that collapse during a stiff fluid domination phase. Such a phase can be realized by a runaway-inflaton model that crosses an inflection point or a sharp feature at the last stage of inflation. Mini PBHs evaporate promptly and reheat the early universe. In addition, we examine two notable implications of this scenario: the possible presence of PBH evaporation remnants in galaxies and a non-zero residual potential energy density for the runaway inflaton that might play the role of the dark energy. We specify the parameter space that this scenario can be realized and we find that a transit PBH domination phase is necessary due to gravitational wave (GW) constraints. A distinct prediction of the scenario is a compound GW signal that might be probed by current and future experiments. We also demonstrate our results employing an explicit inflation model. Full article
(This article belongs to the Special Issue Latest Developments in the Quest for the Unification of Cosmic Inflation and Dark Energy)
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Review

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43 pages, 4748 KiB  
Review
Quintessential Inflation: A Tale of Emergent and Broken Symmetries
by Dario Bettoni and Javier Rubio
Galaxies 2022, 10(1), 22; https://doi.org/10.3390/galaxies10010022 - 27 Jan 2022
Cited by 25 | Viewed by 3115
Abstract
Quintessential inflation provides a unified description of inflation and dark energy in terms of a single scalar degree of freedom, the cosmon. We present here a comprehensive overview of this appealing paradigm, highlighting its key ingredients and keeping a reasonable and homogeneous level [...] Read more.
Quintessential inflation provides a unified description of inflation and dark energy in terms of a single scalar degree of freedom, the cosmon. We present here a comprehensive overview of this appealing paradigm, highlighting its key ingredients and keeping a reasonable and homogeneous level of details. After summarizing the cosmological evolution in a simple canonical case, we discuss how quintessential inflation can be embedded in a more general scalar-tensor formulation and its relation to variable gravity scenarios. Particular emphasis is placed on the role played by symmetries. In particular, we discuss the evolution of the cosmon field in terms of ultraviolet and infrared fixed points potentially appearing in quantum gravity formulations and leading to the emergence of scale invariance in the early and late Universe. The second part of the review is devoted to the exploration of the phenomenological consequences of the paradigm. First, we discuss how direct couplings of the cosmon field to matter may affect neutrinos masses and primordial structure formation. Second, we describe how Ricci-mediated couplings to spectator fields can trigger the spontaneous symmetry breaking of internal symmetries such as, but not limited to, global U(1) or Z2 symmetries, and affect a large variety of physical processes in the early Universe. Full article
(This article belongs to the Special Issue Latest Developments in the Quest for the Unification of Cosmic Inflation and Dark Energy)
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58 pages, 952 KiB  
Review
A Review of Quintessential Inflation
by Jaume de Haro and Llibert Aresté Saló
Galaxies 2021, 9(4), 73; https://doi.org/10.3390/galaxies9040073 - 1 Oct 2021
Cited by 28 | Viewed by 2299
Abstract
Some of the most important quintessential inflation scenarios, such as the Peebles–Vilenkin model, are described in detail. These models are able to explain the early- and late-time accelerated expansions of our universe, and the phase transition from the end of inflation to the [...] Read more.
Some of the most important quintessential inflation scenarios, such as the Peebles–Vilenkin model, are described in detail. These models are able to explain the early- and late-time accelerated expansions of our universe, and the phase transition from the end of inflation to the beginning of kination where the adiabatic evolution of the universe was broken in order to produce enough particles to reheat the universe with a viable temperature, thereby aligning with the Hot Big Bang universe. In addition, while considering the reheating to be due to the gravitational production of superheavy particles conformally coupled to gravity, we checked that the considered scenarios do not suffer problems due to the overproduction of gravitational waves at the end of inflation, and thus the validity of Big Bang nucleosynthesis is preserved. Full article
(This article belongs to the Special Issue Latest Developments in the Quest for the Unification of Cosmic Inflation and Dark Energy)
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