Special Issue "Varying Constants and Fundamental Cosmology"

A special issue of Universe (ISSN 2218-1997).

Deadline for manuscript submissions: closed (1 April 2017)

Special Issue Editors

Guest Editor
Prof. Mariusz P. Dąbrowski

Cosmology Group, Institute of Physics, University of Szczecin, Wielkopolska 15, 70-451 Szczecin, Poland
Website | E-Mail
Interests: general relativity and cosmology; alternative gravities; superstring and brane cosmology; quantum cosmology; standard and non-standard cosmological singularities; varying constants (theory, observations, experiment); superstring landscape and the multiverse
Guest Editor
Dr. Manuel Krämer

Cosmology Group, Institute of Physics, University of Szczecin, Wielkopolska 15, 70-451 Szczecin, Poland
Website | E-Mail
Interests: general relativity; quantum gravity and quantum cosmology; CMB and density perturbations due to quantum effects, spacetime singularities, multiverse and varying constants
Guest Editor
Dr. Vincenzo Salzano

Cosmology Group, Institute of Physics, University of Szczecin, Wielkopolska 15, 70-451 Szczecin, Poland
Website | E-Mail
Interests: observational cosmology; variability of the physical constants (theory and observations); dark energy

Special Issue Information

Dear Colleagues,

This Special Issue will be the proceedings of the conference “Varying Constants and Fundamental Cosmology”, which will take place in Szczecin, Poland, 12–17 September, 2016. This is the fourth of the fundamental cosmology conferences organized by the Cosmology Group, University of Szczecin (after Cosmofun’2005, Grasscosmofun’09, Multicosmofun’12).

The task of the conference is to bring together specialists dealing with the problems of varying (dynamical) physical constants, standard and fundamental cosmology (based on unification particle physics theories, such as superstring/brane theories, alternative gravities, etc.) and the multiverse idea (Everett many-world interpretation, quantum entanglement, superstring landscape, etc.), who want to exchange current ideas on these topics. Renowned specialists in the fields have confirmed their attendance. Among them, three Templeton Prize Awardees dealing with cosmological implications of varying constants and the mathematical structure of the universe John D. Barrow, Paul C.W. Davies and Michael Heller, the founder of the idea of the anthropic principle–Brandon Carter—as well as many specialists in the field of observational tests of varying constants, such as John Webb, Victor Flambaum, and Michael Murphy. The program of the conference will contain five plenary morning sessions and four afternoon parallel sessions. Morning sessions will mainly (though not exceptionally) be devoted to both theoretical and observational aspects of varying constants, while parallel sessions will also contain a great deal of standard and fundamental cosmology (dark energy, dark matter, inflation and the early universe, cosmic microwave background, gravitational waves, quantum gravity and cosmology, observational cosmology).

This Special Issue of Universe will contain longer review articles by invited speakers, as well as selected by the session conveners short invited articles by parallel session speakers.

For more information about the conference idea see: https://indico.cern.ch/e/varcosmo16

Prof. Mariusz P. Dąbrowski
Dr. Manuel Krämer
Dr. Vincenzo Salzano
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 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. Universe is an international peer-reviewed open access quarterly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) is waived for well-prepared manuscripts submitted to this issue. 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.

Published Papers (30 papers)

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Research

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Open AccessArticle Modified Gravity with Vector Distortion and Cosmological Applications
Universe 2017, 3(2), 47; doi:10.3390/universe3020047
Received: 7 April 2017 / Revised: 14 May 2017 / Accepted: 19 May 2017 / Published: 24 May 2017
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Abstract
We briefly review the basics of Weyl geometry and its natural extension by a general linear ”distortion” of the metric connection by a vector field. A special class of the connections has torsion but retains the Weyl’s semi-metricity condition. We present ghost-free gravitational
[...] Read more.
We briefly review the basics of Weyl geometry and its natural extension by a general linear ”distortion” of the metric connection by a vector field. A special class of the connections has torsion but retains the Weyl’s semi-metricity condition. We present ghost-free gravitational theories in this geometrical setup and highlight their possible cosmological applications, such as new self-tuning solutions and new bouncing solutions found in the quadratic-curvature theories. The vector distortion can mimic the cosmological effects of dark matter. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessArticle Lemaître Class Dark Energy Model for Relaxing Cosmological Constant
Universe 2017, 3(2), 39; doi:10.3390/universe3020039
Received: 20 January 2017 / Revised: 23 March 2017 / Accepted: 2 May 2017 / Published: 4 May 2017
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Abstract
Cosmological constant corresponds to the maximally symmetric cosmological term with the equation of state p=ρ. Introducing a cosmological term with the reduced symmetry, pr=ρ in the spherically symmetric case, makes cosmological constant intrinsically variable component
[...] Read more.
Cosmological constant corresponds to the maximally symmetric cosmological term with the equation of state p = ρ . Introducing a cosmological term with the reduced symmetry, p r = ρ in the spherically symmetric case, makes cosmological constant intrinsically variable component of a variable cosmological term which describes time-dependent and spatially inhomogeneous vacuum dark energy. Relaxation of the cosmological constant from the big initial value to the presently observed value can be then described in general setting by the spherically symmetric cosmology of the Lemaître class. We outline in detail the cosmological model with the global structure of the de Sitter spacetime distinguished by the holographic principle as the only stable product of quantum evaporation of the cosmological horizon entirely determined by its quantum dynamics. Density of the vacuum dark energy is presented by semiclassical description of vacuum polarization in the spherically symmetric gravitational field, and its initial value is chosen at the GUT scale. The final non-zero value of the cosmological constant is tightly fixed by the quantum dynamics of evaporation and appears in the reasonable agreement with its observational value. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessArticle Effective Gravitational “Constant” in Scalar-(Curvature)Tensor and Scalar-Torsion Gravities
Universe 2017, 3(2), 37; doi:10.3390/universe3020037
Received: 1 February 2017 / Revised: 9 April 2017 / Accepted: 18 April 2017 / Published: 24 April 2017
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Abstract
In theories where a scalar field couples nonminimally to gravity, the effective gravitational “constant” becomes dependent on the value of the scalar field. This note first gives a brief review on how the cosmological evolution provides a dynamical stabilization for the gravitational “constant”
[...] Read more.
In theories where a scalar field couples nonminimally to gravity, the effective gravitational “constant” becomes dependent on the value of the scalar field. This note first gives a brief review on how the cosmological evolution provides a dynamical stabilization for the gravitational “constant” as the system relaxes towards general relativity in matter dominated and potential dominated regimes for scalar-(curvature)tensor and scalar-torsion gravities. Second part summarizes the radius dependence of the gravitational “constant” around a point mass in the parametrized post-Newtonian formalism for scalar-tensor and multiscalar-tensor gravity. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
Open AccessArticle Evaluating the New Automatic Method for the Analysis of Absorption Spectra Using Synthetic Spectra
Universe 2017, 3(2), 34; doi:10.3390/universe3020034
Received: 1 February 2017 / Revised: 11 March 2017 / Accepted: 29 March 2017 / Published: 5 April 2017
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Abstract
We recently presented a new “artificial intelligence” method for the analysis of high-resolution absorption spectra (Bainbridge and Webb, Mon. Not. R. Astron. Soc. 2017, doi:10.1093/mnras/stx179). This new method unifies three established numerical methods: a genetic algorithm (GVPFIT); non-linear least-squares optimisation with parameter
[...] Read more.
We recently presented a new “artificial intelligence” method for the analysis of high-resolution absorption spectra (Bainbridge and Webb, Mon. Not. R. Astron. Soc. 2017, doi:10.1093/mnras/stx179). This new method unifies three established numerical methods: a genetic algorithm (GVPFIT); non-linear least-squares optimisation with parameter constraints (VPFIT); and Bayesian Model Averaging (BMA). In this work, we investigate the performance of GVPFIT and BMA over a broad range of velocity structures using synthetic spectra. We found that this new method recovers the velocity structures of the absorption systems and accurately estimates variation in the fine structure constant. Studies such as this one are required to evaluate this new method before it can be applied to the analysis of large sets of absorption spectra. This is the first time that a sample of synthetic spectra has been utilised to investigate the analysis of absorption spectra. Probing the variation of nature’s fundamental constants (such as the fine structure constant), through the analysis of absorption spectra, is one of the most direct ways of testing the universality of physical laws. This “artificial intelligence” method provides a way to avoid the main limiting factor, i.e., human interaction, in the analysis of absorption spectra. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessArticle From Quantum to Cosmological Regime. The Role of Forcing and Exotic 4-Smoothness
Universe 2017, 3(2), 31; doi:10.3390/universe3020031
Received: 30 January 2017 / Revised: 5 March 2017 / Accepted: 21 March 2017 / Published: 27 March 2017
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Abstract
Recently, a cosmological model based on smooth open 4-manifolds admitting non-standard smoothness structures was proposed. The manifolds are exotic versions of R4 and S3×R. The model has been developed further and proven to be capable of obtaining some
[...] Read more.
Recently, a cosmological model based on smooth open 4-manifolds admitting non-standard smoothness structures was proposed. The manifolds are exotic versions of R 4 and S 3 × R . The model has been developed further and proven to be capable of obtaining some realistic cosmological parameters from these exotic smoothings. The important problem of the quantum origins of the exotic smoothness of space-time is addressed here. It is shown that the algebraic structure of the quantum-mechanical lattice of projections enforces exotic smoothness on R n . Since the only possibility for such a structure is exotic R 4 , it is found to be a reasonable explanation of the large-scale four-dimensionality of space-time. This is based on our recent research indicating the role of set-theoretic forcing in quantum mechanics. In particular, it is shown that a distributive lattice of projections implies the standard smooth structure on R 4 . Two examples of models valid for cosmology are discussed. The important result that the cosmological constant can be identified with the constant curvature of the embedding ( exotic R 4 ) R 4 is referred. . The calculations are in good agreement with the observed small value of the dark energy density. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
Open AccessArticle Spin-Field Correspondence
Universe 2017, 3(2), 29; doi:10.3390/universe3020029
Received: 4 January 2017 / Revised: 15 March 2017 / Accepted: 21 March 2017 / Published: 23 March 2017
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Abstract
In the recent article Phys. Lett. B 2016, 759, 424–429, a new class of field theories called Nonlinear Field Space Theory was proposed. In this approach, the standard field theories are considered as linear approximations to some more general theories characterized
[...] Read more.
In the recent article Phys. Lett. B 2016, 759, 424–429, a new class of field theories called Nonlinear Field Space Theory was proposed. In this approach, the standard field theories are considered as linear approximations to some more general theories characterized by nonlinear field phase spaces. The case of spherical geometry is especially interesting due to its relation with the spin physics. Here, we explore this possibility, showing that classical scalar field theory with such a field space can be viewed as a perturbation of a continuous spin system. In this picture, the spin precession and the scalar field excitations are dual descriptions of the same physics. The duality is studied in the example of the Heisenberg model. It is shown that the Heisenberg model coupled to a magnetic field leads to a non-relativistic scalar field theory, characterized by quadratic dispersion relation. Finally, on the basis of analysis of the relation between the spin phase space and the scalar field theory, we propose the Spin-Field correspondence between the known types of fields and the corresponding spin systems. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessArticle On the Causality and K-Causality between Measures
Universe 2017, 3(1), 27; doi:10.3390/universe3010027
Received: 31 January 2017 / Revised: 1 March 2017 / Accepted: 11 March 2017 / Published: 20 March 2017
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Abstract
Drawing from the optimal transport theory adapted to the Lorentzian setting, we propose and study the extension of the Sorkin–Woolgar causal relation K+ onto the space of Borel probability measures on a given spacetime. We show that it retains its fundamental properties
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Drawing from the optimal transport theory adapted to the Lorentzian setting, we propose and study the extension of the Sorkin–Woolgar causal relation K + onto the space of Borel probability measures on a given spacetime. We show that it retains its fundamental properties of transitivity and closedness. Furthermore, we list and prove several characterizations of this relation, including the “measure-theoretic” analogue of the characterization of K + in terms of time functions. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
Open AccessArticle Cosmology with Varying Constants from a Thermodynamic Viewpoint
Universe 2017, 3(1), 26; doi:10.3390/universe3010026
Received: 31 January 2017 / Revised: 6 March 2017 / Accepted: 13 March 2017 / Published: 17 March 2017
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Abstract
We study the variation of fundamental constants in cosmology while dealing with thermodynamic aspects of gravity. We focus on the variation of the speed of light, c, and Newton’s gravitational constant, G, with respect to cosmic time. We find the constraints
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We study the variation of fundamental constants in cosmology while dealing with thermodynamic aspects of gravity. We focus on the variation of the speed of light, c, and Newton’s gravitational constant, G, with respect to cosmic time. We find the constraints on the possible variation of these constants by comparing varying constants of cosmological models with the latest observational data. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
Open AccessArticle Cosmological Perturbations in Phantom Dark Energy Models
Universe 2017, 3(1), 22; doi:10.3390/universe3010022
Received: 27 January 2017 / Revised: 24 February 2017 / Accepted: 26 February 2017 / Published: 6 March 2017
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Abstract
The ΛCDM paradigm, characterised by a constant equation of state w=1 for dark energy, is the model that better fits observations. However, the same observations strongly support the possibility of a dark energy content where the corresponding equation of state
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The ΛCDM paradigm, characterised by a constant equation of state w = 1 for dark energy, is the model that better fits observations. However, the same observations strongly support the possibility of a dark energy content where the corresponding equation of state is close to but slightly smaller than 1 . In this regard, we focus on three different models where the dark energy content is described by a perfect fluid with an equation of state w 1 which can evolve or not. The three proposals show very similar behaviour at present, while the asymptotic evolution of each model drives the Universe to different abrupt events known as (i) Big Rip; (ii) Little Rip (LR); and (iii) Little Sibling of the Big Rip. With the aim of comparing these models and finding possible imprints in their predicted matter distribution, we compute the matter power spectrum and the growth rate f σ 8 . We conclude that the model which induces a LR seems to be favoured by observations. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessArticle 3-Form Cosmology: Phantom Behaviour, Singularities and Interactions
Universe 2017, 3(1), 21; doi:10.3390/universe3010021
Received: 27 January 2017 / Revised: 19 February 2017 / Accepted: 26 February 2017 / Published: 3 March 2017
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Abstract
The latest cosmological observations by the Planck collaboration (and combined with others) are compatible with a phantom-like behaviour (w<1) for the dark energy equation of state that drives the current acceleration of the Universe. With this mindset, we
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The latest cosmological observations by the Planck collaboration (and combined with others) are compatible with a phantom-like behaviour ( w < 1 ) for the dark energy equation of state that drives the current acceleration of the Universe. With this mindset, we look into models where dark energy is described by a 3-form field minimally coupled to gravity. When compared to a scalar field, these models have the advantage of more naturally accommodating a cosmological-constant and phantom-like behaviours. We show how the latter happens for a fairly general class of positive-valued potentials, and through a dynamical system approach, we find that in such cases the 3-form field leads the Universe into a Little Sibling of the Big Rip singular event into the future. In this work, we explore the possibility of avoiding such singularity via an interaction in the dark sector between cold dark matter and the 3-form field. For the kind of interactions considered, we deduce a condition for replacing the LSBR by a late time de Sitter phase. For specific examples of interactions that meet this condition, we look for distinctive imprints in the statefinder hierarchy { S 3 ( 1 ) ; S 4 ( 1 ) } , { S 3 ( 1 ) ; S 5 ( 1 ) } , and in the growth rate of matter, ϵ ( z ) , through the composite null diagnostic (CND). Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessArticle Non-Standard Hierarchies of the Runnings of the Spectral Index in Inflation
Universe 2017, 3(1), 17; doi:10.3390/universe3010017
Received: 30 January 2017 / Accepted: 26 February 2017 / Published: 2 March 2017
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Abstract
Recent analyses of cosmic microwave background surveys have revealed hints that there may be a non-trivial running of the running of the spectral index. If future experiments were to confirm these hints, it would prove a powerful discriminator of inflationary models, ruling out
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Recent analyses of cosmic microwave background surveys have revealed hints that there may be a non-trivial running of the running of the spectral index. If future experiments were to confirm these hints, it would prove a powerful discriminator of inflationary models, ruling out simple single field models. We discuss how isocurvature perturbations in multi-field models can be invoked to generate large runnings in a non-standard hierarchy, and find that a minimal model capable of practically realising this would be a two-field model with a non-canonical kinetic structure. We also consider alternative scenarios such as variable speed-of-light models and canonical quantum gravity effects and their implications for runnings of the spectral index. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
Open AccessArticle Bell Violation in Primordial Cosmology
Universe 2017, 3(1), 13; doi:10.3390/universe3010013
Received: 27 December 2016 / Revised: 7 February 2017 / Accepted: 8 February 2017 / Published: 17 February 2017
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Abstract
In this paper, we have worked on the possibility of setting up an Bell’s inequality violating experiment in the context of primordial cosmology following the fundamental principles of quantum mechanics. To set up this proposal, we have introduced a model-independent theoretical framework using
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In this paper, we have worked on the possibility of setting up an Bell’s inequality violating experiment in the context of primordial cosmology following the fundamental principles of quantum mechanics. To set up this proposal, we have introduced a model-independent theoretical framework using which we have studied the creation of new massive particles for the scalar fluctuations in the presence of an additional time-dependent mass parameter. Next we explicitly computed the one-point and two-point correlation functions from this setup. Then, we comment on the measurement techniques of isospin breaking interactions of newly introduced massive particles and its further prospects. After that, we give an example of the string theory-originated axion monodromy model in this context. Finally, we provide a bound on the heavy particle mass parameter for any arbitrary spin field. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessArticle Nonlinear Gravitational Waves as Dark Energy in Warped Spacetimes
Universe 2017, 3(1), 11; doi:10.3390/universe3010011
Received: 14 December 2016 / Revised: 8 February 2017 / Accepted: 10 February 2017 / Published: 15 February 2017
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Abstract
We find an azimuthal-angle dependent approximate wave like solution to second order on a warped five-dimensional manifold with a self-gravitating U(1) scalar gauge field (cosmic string) on the brane using the multiple-scale method. The spectrum of the several orders of approximation show maxima
[...] Read more.
We find an azimuthal-angle dependent approximate wave like solution to second order on a warped five-dimensional manifold with a self-gravitating U(1) scalar gauge field (cosmic string) on the brane using the multiple-scale method. The spectrum of the several orders of approximation show maxima of the energy distribution dependent on the azimuthal-angle and the winding numbers of the subsequent orders of the scalar field. This breakup of the quantized flux quanta does not lead to instability of the asymptotic wavelike solution due to the suppression of the n-dependency in the energy momentum tensor components by the warp factor. This effect is triggered by the contribution of the five dimensional Weyl tensor on the brane. This contribution can be understood as dark energy and can trigger the self-acceleration of the universe without the need of a cosmological constant. There is a striking relation between the symmetry breaking of the Higgs field described by the winding number and the SO(2) breaking of the axially symmetric configuration into a discrete subgroup of rotations of about 180 . The discrete sequence of non-axially symmetric deviations, cancelled by the emission of gravitational waves in order to restore the SO(2) symmetry, triggers the pressure T z z for discrete values of the azimuthal-angle. There could be a possible relation between the recently discovered angle-preferences of polarization axes of quasars on large scales and our theoretical predicted angle-dependency and this could be evidence for the existence of cosmic strings. Careful comparison of this spectrum of extremal values of the first and second order φ-dependency and the distribution of the alignment of the quasar polarizations is necessary. This can be accomplished when more observational data become available. It turns out that, for late time, the vacuum 5D spacetime is conformally invariant if the warp factor fulfils the equation of a vibrating “drum”, describing standing normal modes of the brane. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
Open AccessArticle The Relation between Fundamental Constants and Particle Physics Parameters
Universe 2017, 3(1), 6; doi:10.3390/universe3010006
Received: 16 December 2016 / Revised: 12 January 2017 / Accepted: 13 January 2017 / Published: 24 January 2017
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Abstract
The observed constraints on the variability of the proton to electron mass ratio μ and the fine structure constant α are used to establish constraints on the variability of the Quantum Chromodynamic Scale and a combination of the Higgs Vacuum Expectation Value and
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The observed constraints on the variability of the proton to electron mass ratio μ and the fine structure constant α are used to establish constraints on the variability of the Quantum Chromodynamic Scale and a combination of the Higgs Vacuum Expectation Value and the Yukawa couplings. Further model dependent assumptions provide constraints on the Higgs VEV and the Yukawa couplings separately. A primary conclusion is that limits on the variability of dimensionless fundamental constants such as μ and α provide important constraints on the parameter space of new physics and cosmologies. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Review

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Open AccessReview A Review on the Cosmology of the de Sitter Horndeski Models
Universe 2017, 3(2), 33; doi:10.3390/universe3020033
Received: 31 January 2017 / Revised: 24 March 2017 / Accepted: 27 March 2017 / Published: 31 March 2017
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Abstract
We review the most general scalar-tensor cosmological models with up to second-order derivatives in the field equations that have a fixed spatially flat de Sitter critical point independent of the material content or vacuum energy. This subclass of the Horndeski Lagrangian is capable
[...] Read more.
We review the most general scalar-tensor cosmological models with up to second-order derivatives in the field equations that have a fixed spatially flat de Sitter critical point independent of the material content or vacuum energy. This subclass of the Horndeski Lagrangian is capable of dynamically adjusting any value of the vacuum energy of the matter fields at the critical point. We present the cosmological evolution of the linear models and the non-linear models with shift symmetry. We come to the conclusion that the shift symmetric non-linear models can deliver a viable background compatible with current observations. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessReview The Geometry of Noncommutative Spacetimes
Universe 2017, 3(1), 25; doi:10.3390/universe3010025
Received: 11 February 2017 / Revised: 10 March 2017 / Accepted: 12 March 2017 / Published: 16 March 2017
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Abstract
We review the concept of ‘noncommutative spacetime’ approached from an operational stand-point and explain how to endow it with suitable geometrical structures. The latter involves i.a. the causal structure, which we illustrate with a simple—‘almost-commutative’—example. Furthermore, we trace the footprints of noncommutive geometry
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We review the concept of ‘noncommutative spacetime’ approached from an operational stand-point and explain how to endow it with suitable geometrical structures. The latter involves i.a. the causal structure, which we illustrate with a simple—‘almost-commutative’—example. Furthermore, we trace the footprints of noncommutive geometry in the foundations of quantum field theory. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessReview Dark Energy and Spacetime Symmetry
Universe 2017, 3(1), 20; doi:10.3390/universe3010020
Received: 23 January 2017 / Revised: 27 February 2017 / Accepted: 1 March 2017 / Published: 3 March 2017
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Abstract
The Petrov classification of stress-energy tensors provides a model-independent definition of a vacuum by the algebraic structure of its stress-energy tensor and implies the existence of vacua whose symmetry is reduced as compared with the maximally symmetric de Sitter vacuum associated with the
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The Petrov classification of stress-energy tensors provides a model-independent definition of a vacuum by the algebraic structure of its stress-energy tensor and implies the existence of vacua whose symmetry is reduced as compared with the maximally symmetric de Sitter vacuum associated with the Einstein cosmological term. This allows to describe a vacuum in general setting by dynamical vacuum dark fluid, presented by a variable cosmological term with the reduced symmetry which makes vacuum fluid essentially anisotropic and allows it to be evolving and clustering. The relevant solutions to the Einstein equations describe regular cosmological models with time-evolving and spatially inhomogeneous vacuum dark energy, and compact vacuum objects generically related to a dark energy: regular black holes, their remnants and self-gravitating vacuum solitons with de Sitter vacuum interiors—which can be responsible for observational effects typically related to a dark matter. The mass of objects with de Sitter interior is generically related to vacuum dark energy and to breaking of space-time symmetry. In the cosmological context spacetime symmetry provides a mechanism for relaxing cosmological constant to a needed non-zero value. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Other

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Open AccessConference Report Observational Consequences of an Interacting Multiverse
Universe 2017, 3(2), 49; doi:10.3390/universe3020049 (registering DOI)
Received: 10 April 2017 / Revised: 8 May 2017 / Accepted: 23 May 2017 / Published: 25 May 2017
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Abstract
The observability of the multiverse is at the very root of its physical significance as a scientific proposal. In this conference we present, within the third quantization formalism, an interacting scheme between the wave functions of different universes and analyze the effects of
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The observability of the multiverse is at the very root of its physical significance as a scientific proposal. In this conference we present, within the third quantization formalism, an interacting scheme between the wave functions of different universes and analyze the effects of some particular values of the coupling function. One of the main consequences of the interaction between universes can be the appearance of a pre-inflationary stage in the evolution of the universes that might leave observable consequences in the properties of the CMB. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report Quantum Cosmology and Varying Physical Constants
Universe 2017, 3(2), 46; doi:10.3390/universe3020046
Received: 2 April 2017 / Revised: 14 May 2017 / Accepted: 15 May 2017 / Published: 23 May 2017
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Abstract
The main task of this review is to discuss quantum cosmology minisuperspace models based on the Wheeler–DeWitt equation, which apart from the standard matter and 3-geometry configuration degrees of freedom, allow those related to the variability of physical constants—varying speed of light (VSL)
[...] Read more.
The main task of this review is to discuss quantum cosmology minisuperspace models based on the Wheeler–DeWitt equation, which apart from the standard matter and 3-geometry configuration degrees of freedom, allow those related to the variability of physical constants—varying speed of light (VSL) c and varying gravitational constant G. The tunneling probability of the universe “from nothing” to the Friedmann phase will be given for such varying constants minisuperspace models. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report Blind Spots for Direct Detection with Simplified DM Models and the LHC
Universe 2017, 3(2), 41; doi:10.3390/universe3020041
Received: 1 February 2017 / Revised: 28 April 2017 / Accepted: 2 May 2017 / Published: 11 May 2017
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Abstract
Using the existing simplified model framework, we build several dark matter models which have suppressed spin-independent scattering cross section. We show that the scattering cross section can vanish due to interference effects with models obtained by simple combinations of simplified models. For weakly
[...] Read more.
Using the existing simplified model framework, we build several dark matter models which have suppressed spin-independent scattering cross section. We show that the scattering cross section can vanish due to interference effects with models obtained by simple combinations of simplified models. For weakly interacting massive particle (WIMP) masses ≳10 GeV, collider limits are usually much weaker than the direct detection limits coming from LUX or XENON100. However, for our model combinations, LHC analyses are more competitive for some parts of the parameter space. The regions with direct detection blind spots can be strongly constrained from the complementary use of several Large Hadron Collider (LHC) searches like mono-jet, jets + missing transverse energy, heavy vector resonance searches, etc. We evaluate the strongest limits for combinations of scalar + vector, “squark” + vector, and scalar + “squark” mediator, and present the LHC 14 TeV projections. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report Nucleosynthesis Predictions and High-Precision Deuterium Measurements
Universe 2017, 3(2), 44; doi:10.3390/universe3020044
Received: 9 January 2017 / Revised: 25 April 2017 / Accepted: 3 May 2017 / Published: 9 May 2017
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Abstract
Two new high-precision measurements of the deuterium abundance from absorbers along the line of sight to the quasar PKS1937–1009 were presented. The absorbers have lower neutral hydrogen column densities (N(HI) ≈ 18 cm2) than for previous high-precision measurements, boding well
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Two new high-precision measurements of the deuterium abundance from absorbers along the line of sight to the quasar PKS1937–1009 were presented. The absorbers have lower neutral hydrogen column densities (N(HI) ≈ 18 cm 2 ) than for previous high-precision measurements, boding well for further extensions of the sample due to the plenitude of low column density absorbers. The total high-precision sample now consists of 12 measurements with a weighted average deuterium abundance of D/H = 2 . 55 ± 0 . 02 × 10 5 . The sample does not favour a dipole similar to the one detected for the fine structure constant. The increased precision also calls for improved nucleosynthesis predictions. For that purpose we have updated the public AlterBBN code including new reactions, updated nuclear reaction rates, and the possibility of adding new physics such as dark matter. The standard Big Bang Nucleosynthesis prediction of D/H = 2 . 456 ± 0 . 057 × 10 5 is consistent with the observed value within 1.7 standard deviations. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report Quantum Cosmology of the Big Rip: Within GR and in a Modified Theory of Gravity
Universe 2017, 3(2), 36; doi:10.3390/universe3020036
Received: 8 March 2017 / Revised: 7 April 2017 / Accepted: 12 April 2017 / Published: 14 April 2017
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Abstract
Quantum gravity is the theory that is expected to successfully describe systems that are under strong gravitational effects while at the same time being of an extreme quantum nature. When this principle is applied to the universe as a whole, we use what
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Quantum gravity is the theory that is expected to successfully describe systems that are under strong gravitational effects while at the same time being of an extreme quantum nature. When this principle is applied to the universe as a whole, we use what is commonly named “quantum cosmology”. So far we do not have a definite quantum theory of gravity or cosmology, but we have several promising approaches. Here we will review the application of the Wheeler–DeWitt formalism to the late-time universe, where it might face a Big Rip future singularity. The Big Rip singularity is the most virulent future dark energy singularity which can happen not only in general relativity but also in some modified theories of gravity. Our goal in this paper is to review two simple setups of the quantisation of the Big Rip in a Friedmann–Lemaître–Robertson–Walker universe within general relativity and in a modified theory of gravity. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report How to Reconstruct a Varying Speed of Light Signal from Baryon Acoustic Oscillations Surveys
Universe 2017, 3(2), 35; doi:10.3390/universe3020035
Received: 15 January 2017 / Revised: 4 April 2017 / Accepted: 6 April 2017 / Published: 11 April 2017
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Abstract
We describe an alternative way to use future Baryon Acoustic Oscillation observations to perform non-mainstream research. We focus on the so-called Varying Speed of Light theories, in which the speed of light is made to vary in time. Using prescriptions from future BAO
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We describe an alternative way to use future Baryon Acoustic Oscillation observations to perform non-mainstream research. We focus on the so-called Varying Speed of Light theories, in which the speed of light is made to vary in time. Using prescriptions from future BAO surveys (BOSS, DESI, WFirst-2.4 and SKA), we show that, within such surveys, a 1% Varying Speed of Light (VSL) signal could be detected at 3 sigmas confidence level, in the redshift interval [0.75, 1.45]. Smaller signals will be hardly detected. We also discuss some possible problems related to such kinds of observation, in particular, the degeneracy between a VSL signal and a non-null spatial curvature. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
Open AccessConference Report Probing the Gravitational Dependence of the Fine-Structure Constant from Observations of White Dwarf Stars
Universe 2017, 3(2), 32; doi:10.3390/universe3020032
Received: 31 January 2017 / Revised: 13 March 2017 / Accepted: 17 March 2017 / Published: 30 March 2017
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Abstract
Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with an opportunity for a direct observational test. We study a sample of hot white dwarf stars, combining far-UV spectroscopic observations, atomic
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Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with an opportunity for a direct observational test. We study a sample of hot white dwarf stars, combining far-UV spectroscopic observations, atomic physics, atmospheric modelling, and fundamental physics in the search for variation in the fine structure constant. This variation manifests as shifts in the observed wavelengths of absorption lines, such as quadruply ionized iron (FeV) and quadruply ionized nickel (NiV), when compared to laboratory wavelengths. Berengut et al. (Phys. Rev. Lett. 2013, 111, 010801) demonstrated the validity of such an analysis using high-resolution Space Telescope Imaging Spectrograph (STIS) spectra of G191-B2B. We have made three important improvements by: (a) using three new independent sets of laboratory wavelengths; (b) analysing a sample of objects; and (c) improving the methodology by incorporating robust techniques from previous studies towards quasars (the Many Multiplet method). A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. Here we describe our approach and present preliminary results from nine objects using both FeV and NiV. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report Dark Energy Constraints from Espresso Tests of the Stability of Fundamental Couplings
Universe 2017, 3(2), 30; doi:10.3390/universe3020030
Received: 30 January 2017 / Revised: 15 March 2017 / Accepted: 17 March 2017 / Published: 24 March 2017
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Abstract
ESPRESSO is a high-resolution-ultra-stable spectrograph for the Very Large Telescope (VLT), whose commissioning will start in 2017. One of its key science goals is to test the stability of nature’s fundamental couplings with unprecedented accuracy and control of possible systematics. A total of
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ESPRESSO is a high-resolution-ultra-stable spectrograph for the Very Large Telescope (VLT), whose commissioning will start in 2017. One of its key science goals is to test the stability of nature’s fundamental couplings with unprecedented accuracy and control of possible systematics. A total of 27 nights of the ESPRESSO Consortium’s guaranteed time observations (GTO) will be spent on testing the stability of the fine-structure constant and other fundamental couplings. A set of 14 priority optimal targets have been selected for the GTO period. In this work, we discuss the criteria underlying this selection, describe the selected targets, and present some forecasts of the impact of these measurements on fundamental physics and cosmology, focusing on dark energy constraints and using future supernova type Ia surveys as a comparison point. This report is a summary of the results reported in Phys. Rev. D 2016, 94, 123512, to which we refer the reader for further details. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report Quantum Entanglement in the Multiverse
Universe 2017, 3(2), 28; doi:10.3390/universe3020028
Received: 12 January 2017 / Revised: 16 March 2017 / Accepted: 17 March 2017 / Published: 23 March 2017
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In this report, we consider cosmological implications of quantum entanglement between two causally disconnected universes in the multiverse. Supposing that our universe was initially entangled with a causally separated universe, we compute the spectrum of vacuum fluctuations of our universe. To clearly see
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In this report, we consider cosmological implications of quantum entanglement between two causally disconnected universes in the multiverse. Supposing that our universe was initially entangled with a causally separated universe, we compute the spectrum of vacuum fluctuations of our universe. To clearly see the effect of entanglement, we compare it with the spectrum of an initially non-entangled state. It is found that, due to quantum interference, scale-dependent modulations may enter the spectrum for the case of an initially non-entangled state. We discuss that the existence of causally disconnected universes may be experimentally tested by analyzing correlators in detail. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report Infinitesimal Structure of Singularities
Universe 2017, 3(1), 16; doi:10.3390/universe3010016
Received: 9 January 2017 / Revised: 19 February 2017 / Accepted: 20 February 2017 / Published: 27 February 2017
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Abstract
Some important problems of general relativity, such as the quantisation of gravity or classical singularity problems, crucially depend on geometry on very small scales. The so-called synthetic differential geometry—a categorical counterpart of the standard differential geometry—provides a tool to penetrate infinitesimally small portions
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Some important problems of general relativity, such as the quantisation of gravity or classical singularity problems, crucially depend on geometry on very small scales. The so-called synthetic differential geometry—a categorical counterpart of the standard differential geometry—provides a tool to penetrate infinitesimally small portions of space-time. We use this tool to show that on any “infinitesimal neighbourhood” the components of the curvature tensor are themselves infinitesimal, and construct a simplified model in which the curvature singularity disappears, owing to this effect. However, one pays a price for this result. Using topoi as a generalisation of spaces requires a weakening of arithmetic (the existence of infinitesimals) and of logic (to the intuitionistic logic). Is this too high a price to pay for acquiring a new method of solving unsolved problems in physics? Without trying, we shall never know the answer. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
Open AccessConference Report Quantum Correlations in de Sitter Space
Universe 2017, 3(1), 2; doi:10.3390/universe3010002
Received: 5 December 2016 / Revised: 19 December 2016 / Accepted: 20 December 2016 / Published: 1 January 2017
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Abstract
We study quantum correlation of a massive scalar field in a maximally entangled state in de Sitter space. We prepare two observers, one in a global chart and the other in an open chart of de Sitter space. We find that the state
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We study quantum correlation of a massive scalar field in a maximally entangled state in de Sitter space. We prepare two observers, one in a global chart and the other in an open chart of de Sitter space. We find that the state becomes less entangled as the curvature of the open chart gets larger. In particular, for the cases of a massless and a conformally coupled scalar field, the quantum entanglement vanishes in the limit of infinite curvature. However, we find that the quantum discord never disappears, even in the limit that entanglement disappears. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report New Constraints on Spatial Variations of the Fine Structure Constant from Clusters of Galaxies
Universe 2016, 2(4), 34; doi:10.3390/universe2040034
Received: 30 October 2016 / Revised: 6 December 2016 / Accepted: 12 December 2016 / Published: 21 December 2016
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Abstract
We have constrained the spatial variation of the fine structure constant using multi-frequency measurements of the thermal Sunyaev-Zeldovich effect of 618 X-ray selected clusters. Although our results are not competitive with the ones from quasar absorption lines, we improved by a factor 10
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We have constrained the spatial variation of the fine structure constant using multi-frequency measurements of the thermal Sunyaev-Zeldovich effect of 618 X-ray selected clusters. Although our results are not competitive with the ones from quasar absorption lines, we improved by a factor 10 and ∼2.5 previous results from Cosmic Microwave Background power spectrum and from galaxy clusters, respectively. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)
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Open AccessConference Report Experimental Studies on the Lorentz Symmetry in Post-Newtonian Gravity with Pulsars
Universe 2016, 2(4), 29; doi:10.3390/universe2040029
Received: 30 October 2016 / Revised: 17 November 2016 / Accepted: 23 November 2016 / Published: 1 December 2016
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Abstract
Local Lorentz invariance (LLI) is one of the most important fundamental symmetries in modern physics. While the possibility of LLI violation (LLIv) was studied extensively in flat spacetime, its counterpart in gravitational interaction also deserves significant examination from experiments. In this contribution, I
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Local Lorentz invariance (LLI) is one of the most important fundamental symmetries in modern physics. While the possibility of LLI violation (LLIv) was studied extensively in flat spacetime, its counterpart in gravitational interaction also deserves significant examination from experiments. In this contribution, I review several recent studies of LLI in post-Newtonian gravity, using powerful tools of pulsar timing. It shows that precision pulsar timing experiments hold a unique position to probe LLIv in post-Newtonian gravity. Full article
(This article belongs to the Special Issue Varying Constants and Fundamental Cosmology)

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