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Universe
Volume 3
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Universe, Volume 3, Issue 2 (June 2017) – 24 articles

Cover Story (view full-size image): Does the fine structure constant depend on gravitational potential? Hot white dwarf stars are the ideal probe for a relationship between the fine-structure constant and strong gravitational fields, providing us with a direct means of testing this important question. Potential variation manifests itself as shifts in the observed wavelengths of absorption lines when compared to laboratory wavelengths. A successful detection would be the first direct measurement of a gravitational field effect on a bare constant of nature. View the paper
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749 KiB  
Review
Monopole-Based Scenarios of Confinement and Deconfinement in 3D and 4D
by Dmitry Antonov
Universe 2017, 3(2), 50; https://doi.org/10.3390/universe3020050 - 19 Jun 2017
Cited by 6 | Viewed by 4732
Abstract
This review discusses confinement, as well as the topological and critical phenomena, in the gauge theories which provide the condensation of magnetic monopoles. These theories include the 3D SU(N) Georgi-Glashow model, the 4D [U(1)] N - 1 -invariant compact QED , [...] Read more.
This review discusses confinement, as well as the topological and critical phenomena, in the gauge theories which provide the condensation of magnetic monopoles. These theories include the 3D SU(N) Georgi-Glashow model, the 4D [U(1)] N - 1 -invariant compact QED , and the [U(1)] N - 1 -invariant dual Abelian Higgs model. After a general introduction to the string models of confinement, an analytic description of this penomenon is provided at the example of the 3D SU(N) Georgi-Glashow model, with a special emphasis placed on the so-called Casimir scaling of k-string tensions in that model. We further discuss the string representation of the 3D [U(1)] N - 1 -invariant compact QED, as well as of its 4D generalization with the inclusion of the Θ -term. We compare topological effects, which appear in the latter case, with those that take place in the 3D QED extended by the Chern-Simons term. We further discuss the string representation of the ’t Hooft-loop average in the [U(1)] N - 1 -invariant dual Abelian Higgs model extended by the Θ -term, along with the topological effects caused by this term. These topological effects are compared with those occurring in the 3D dual Abelian Higgs model (i.e., the dual Landau-Ginzburg theory) extended by the Chern-Simons term. In the second part of the review, we discuss critical properties of the weakly-coupled 3D confining theories. These theories include the 3D compact QED, along with its fermionic extension, and the 3D Georgi-Glashow model. Full article
(This article belongs to the Special Issue Quark-Gluon Plasma in the Early Universe and in Ultra-Relativistic Heavy-Ion Collisions)
1151 KiB  
Article
A Model of Black Hole Evaporation and 4D Weyl Anomaly
by Hikaru Kawai and Yuki Yokokura
Universe 2017, 3(2), 51; https://doi.org/10.3390/universe3020051 - 16 Jun 2017
Cited by 49 | Viewed by 4606
Abstract
We analyze the time evolution of a spherically-symmetric collapsing matter from the point of view that black holes evaporate by nature. We consider conformal matters and solve the semi-classical Einstein equation [...] Read more.
We analyze the time evolution of a spherically-symmetric collapsing matter from the point of view that black holes evaporate by nature. We consider conformal matters and solve the semi-classical Einstein equation G μ ν = 8 π G 〈 T μ ν 〉 by using the four-dimensional Weyl anomaly with a large c coefficient. Here, 〈 T μ ν 〉 contains the contribution from both the collapsing matter and Hawking radiation. The solution indicates that the collapsing matter forms a dense object and evaporates without horizon or singularity, and it has a surface, but looks like an ordinary black hole from the outside. Any object we recognize as a black hole should be such an object. Full article
(This article belongs to the Collection Open Questions in Black Hole Physics)
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804 KiB  
Conference Report
Observational Consequences of an Interacting Multiverse
by Salvador J. Robles-Pérez
Universe 2017, 3(2), 49; https://doi.org/10.3390/universe3020049 - 25 May 2017
Cited by 4 | Viewed by 3456
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 [...] Read more.
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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1333 KiB  
Review
Classical Collapse to Black Holes and Quantum Bounces: A Review
by Daniele Malafarina
Universe 2017, 3(2), 48; https://doi.org/10.3390/universe3020048 - 25 May 2017
Cited by 91 | Viewed by 6649
Abstract
In the last four decades, different programs have been carried out aiming at understanding the final fate of gravitational collapse of massive bodies once some prescriptions for the behaviour of gravity in the strong field regime are provided. The general picture arising from [...] Read more.
In the last four decades, different programs have been carried out aiming at understanding the final fate of gravitational collapse of massive bodies once some prescriptions for the behaviour of gravity in the strong field regime are provided. The general picture arising from most of these scenarios is that the classical singularity at the end of collapse is replaced by a bounce. The most striking consequence of the bounce is that the black hole horizon may live for only a finite time. The possible implications for astrophysics are important since, if these models capture the essence of the collapse of a massive star, an observable signature of quantum gravity may be hiding in astrophysical phenomena. One intriguing idea that is implied by these models is the possible existence of exotic compact objects, of high density and finite size, that may not be covered by an horizon. The present article outlines the main features of these collapse models and some of the most relevant open problems. The aim is to provide a comprehensive (as much as possible) overview of the current status of the field from the point of view of astrophysics. As a little extra, a new toy model for collapse leading to the formation of a quasi static compact object is presented. Full article
(This article belongs to the Collection Open Questions in Black Hole Physics)
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287 KiB  
Article
Modified Gravity with Vector Distortion and Cosmological Applications
by Jose Beltrán Jiménez and Tomi S. Koivisto
Universe 2017, 3(2), 47; https://doi.org/10.3390/universe3020047 - 24 May 2017
Cited by 17 | Viewed by 3408
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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815 KiB  
Conference Report
Quantum Cosmology and Varying Physical Constants
by Katarzyna Leszczyńska
Universe 2017, 3(2), 46; https://doi.org/10.3390/universe3020046 - 23 May 2017
Cited by 1 | Viewed by 3851
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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2701 KiB  
Conference Report
Blind Spots for Direct Detection with Simplified DM Models and the LHC
by Arghya Choudhury, Kamila Kowalska, Leszek Roszkowski, Enrico Maria Sessolo and Andrew J. Williams
Universe 2017, 3(2), 41; https://doi.org/10.3390/universe3020041 - 11 May 2017
Cited by 8 | Viewed by 3376
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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313 KiB  
Article
The Astrophysical Scales Set by the Cosmological Constant, Black-Hole Thermodynamics and Non-Linear Massive Gravity
by Ivan Arraut
Universe 2017, 3(2), 45; https://doi.org/10.3390/universe3020045 - 10 May 2017
Cited by 20 | Viewed by 3604
Abstract
We calculate explicitly the black-hole temperature for the Schwarzschild de-Sitter solution inside massive gravity by defining the Killing-vector in the direction of the Stückelberg function. We then consider the conditions which an observer in massive gravity has to obey in order to agree [...] Read more.
We calculate explicitly the black-hole temperature for the Schwarzschild de-Sitter solution inside massive gravity by defining the Killing-vector in the direction of the Stückelberg function. We then consider the conditions which an observer in massive gravity has to obey in order to agree with the standard results of General Relativity. Full article
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1021 KiB  
Conference Report
Nucleosynthesis Predictions and High-Precision Deuterium Measurements
by Signe Riemer-Sørensen and Espen Sem Jenssen
Universe 2017, 3(2), 44; https://doi.org/10.3390/universe3020044 - 9 May 2017
Cited by 22 | Viewed by 4180
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 cm − 2 ) than for previous high-precision measurements, boding well [...] Read more.
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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401 KiB  
Article
Mirror QCD and Cosmological Constant
by Roman Pasechnik, George Prokhorov and Oleg Teryaev
Universe 2017, 3(2), 43; https://doi.org/10.3390/universe3020043 - 8 May 2017
Cited by 12 | Viewed by 4415
Abstract
An analog of Quantum Chromo Dynamics (QCD) sector known as mirror QCD (mQCD) can affect the cosmological evolution due to a non-trivial contribution to the Cosmological Constant analogous to that induced by the ground state in non-perturbative QCD. In this work, we explore [...] Read more.
An analog of Quantum Chromo Dynamics (QCD) sector known as mirror QCD (mQCD) can affect the cosmological evolution due to a non-trivial contribution to the Cosmological Constant analogous to that induced by the ground state in non-perturbative QCD. In this work, we explore a plausible hypothesis for trace anomalies cancellation between the usual QCD and mQCD. Such an anomaly cancellation between the two gauge theories, if it exists in Nature, would lead to a suppression or even elimination of their contributions to the Cosmological Constant. The trace anomaly compensation condition and the form of the non-perturbative mQCD coupling constant in the infrared limit have been proposed by analysing a partial non-perturbative solution of the Einstein–Yang-Mills equations of motion. Full article
(This article belongs to the Special Issue Quark-Gluon Plasma in the Early Universe and in Ultra-Relativistic Heavy-Ion Collisions)
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458 KiB  
Article
Quantum Tunneling Radiation from Loop Quantum Black Holes and the Information Loss Paradox
by C. A. S. Silva and Francisco A. Brito
Universe 2017, 3(2), 42; https://doi.org/10.3390/universe3020042 - 8 May 2017
Cited by 2 | Viewed by 4596
Abstract
In this work, we present some results relating to the issue of the Loop Quantum Black Holes (LQBH) thermodynamics by the use of the tunneling radiation formalism. The information loss paradox is also discussed in this context, and we have considered the influence [...] Read more.
In this work, we present some results relating to the issue of the Loop Quantum Black Holes (LQBH) thermodynamics by the use of the tunneling radiation formalism. The information loss paradox is also discussed in this context, and we have considered the influence of back reaction effects. Full article
(This article belongs to the Special Issue Loop Quantum Cosmology and Quantum Black Holes)
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604 KiB  
Review
A Review of Gravitational Waves from Cosmic Domain Walls
by Ken’ichi Saikawa
Universe 2017, 3(2), 40; https://doi.org/10.3390/universe3020040 - 5 May 2017
Cited by 142 | Viewed by 5977
Abstract
In this contribution, we discuss the cosmological scenario where unstable domain walls are formed in the early universe and their late-time annihilation produces a significant amount of gravitational waves. After describing cosmological constraints on long-lived domain walls, we estimate the typical amplitude and [...] Read more.
In this contribution, we discuss the cosmological scenario where unstable domain walls are formed in the early universe and their late-time annihilation produces a significant amount of gravitational waves. After describing cosmological constraints on long-lived domain walls, we estimate the typical amplitude and frequency of gravitational waves observed today. We also review possible extensions of the standard model of particle physics that predict the formation of unstable domain walls and can be probed by observation of relic gravitational waves. It is shown that recent results of pulser timing arrays and direct detection experiments partially exclude the relevant parameter space, and that a much wider parameter space can be covered by the next generation of gravitational wave observatories. Full article
(This article belongs to the Special Issue Gravitational Waves: Prospects after the First Direct Detections)
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447 KiB  
Article
Lemaître Class Dark Energy Model for Relaxing Cosmological Constant
by Irina Dymnikova, Anna Dobosz and Bożena Sołtysek
Universe 2017, 3(2), 39; https://doi.org/10.3390/universe3020039 - 4 May 2017
Cited by 14 | Viewed by 3518
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, p r = − 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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655 KiB  
Article
The Cosmic Causal Mass
by Simen Braeck, Øyvind G. Grøn and Ivar Farup
Universe 2017, 3(2), 38; https://doi.org/10.3390/universe3020038 - 29 Apr 2017
Cited by 2 | Viewed by 3708
Abstract
In order to provide a better understanding of rotating universe models, and in particular the Gödel universe, we discuss the relationship between cosmic rotation and perfect inertial dragging. In this connection, the concept of causal mass is defined in a cosmological context, and [...] Read more.
In order to provide a better understanding of rotating universe models, and in particular the Gödel universe, we discuss the relationship between cosmic rotation and perfect inertial dragging. In this connection, the concept of causal mass is defined in a cosmological context, and discussed in relation to the cosmic inertial dragging effect. Then, we calculate the mass inside the particle horizon of the flat ΛCDM-model integrated along the past light cone. The calculation shows that the Schwarzschild radius of this mass is around three times the radius of the particle horizon. This indicates that there is close to perfect inertial dragging in our universe. Hence, the calculation provides an explanation for the observation that the swinging plane of a Foucault pendulum follows the stars. Full article
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267 KiB  
Article
Effective Gravitational “Constant” in Scalar-(Curvature)Tensor and Scalar-Torsion Gravities
by Laur Järv
Universe 2017, 3(2), 37; https://doi.org/10.3390/universe3020037 - 24 Apr 2017
Cited by 5 | Viewed by 3263
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)
264 KiB  
Conference Report
Quantum Cosmology of the Big Rip: Within GR and in a Modified Theory of Gravity
by Mariam Bouhmadi-López, Imanol Albarran and Che-Yu Chen
Universe 2017, 3(2), 36; https://doi.org/10.3390/universe3020036 - 14 Apr 2017
Cited by 5 | Viewed by 4891
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 [...] Read more.
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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384 KiB  
Conference Report
How to Reconstruct a Varying Speed of Light Signal from Baryon Acoustic Oscillations Surveys
by Vincenzo Salzano
Universe 2017, 3(2), 35; https://doi.org/10.3390/universe3020035 - 11 Apr 2017
Cited by 4 | Viewed by 2656
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 [...] Read more.
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)
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Article
Evaluating the New Automatic Method for the Analysis of Absorption Spectra Using Synthetic Spectra
by Matthew B. Bainbridge and John K. Webb
Universe 2017, 3(2), 34; https://doi.org/10.3390/universe3020034 - 5 Apr 2017
Cited by 15 | Viewed by 3190
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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246 KiB  
Review
A Review on the Cosmology of the de Sitter Horndeski Models
by Nelson J. Nunes, Prado Martín-Moruno and Francisco S. N. Lobo
Universe 2017, 3(2), 33; https://doi.org/10.3390/universe3020033 - 31 Mar 2017
Cited by 7 | Viewed by 3059
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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209 KiB  
Conference Report
Probing the Gravitational Dependence of the Fine-Structure Constant from Observations of White Dwarf Stars
by Matthew B. Bainbridge, Martin A. Barstow, Nicole Reindl, W.-Ü Lydia Tchang-Brillet, Thomas R. Ayres, John K. Webb, John D. Barrow, Jiting Hu, Jay B. Holberg, Simon P. Preval, Wim Ubachs, Vladimir A. Dzuba, Victor V. Flambaum, Vincent Dumont and Julian C. Berengut
Universe 2017, 3(2), 32; https://doi.org/10.3390/universe3020032 - 30 Mar 2017
Cited by 30 | Viewed by 7647
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 [...] Read more.
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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268 KiB  
Article
From Quantum to Cosmological Regime. The Role of Forcing and Exotic 4-Smoothness
by Jerzy Król, Torsten Asselmeyer-Maluga, Krzysztof Bielas and Paweł Klimasara
Universe 2017, 3(2), 31; https://doi.org/10.3390/universe3020031 - 27 Mar 2017
Cited by 11 | Viewed by 3706
Abstract
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 [...] 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)
278 KiB  
Conference Report
Dark Energy Constraints from Espresso Tests of the Stability of Fundamental Couplings
by Ana C. O. Leite, Carlos J. A. P. Martins and Paolo Molaro
Universe 2017, 3(2), 30; https://doi.org/10.3390/universe3020030 - 24 Mar 2017
Cited by 3 | Viewed by 2929
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 [...] Read more.
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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Article
Spin-Field Correspondence
by Jakub Mielczarek
Universe 2017, 3(2), 29; https://doi.org/10.3390/universe3020029 - 23 Mar 2017
Cited by 10 | Viewed by 3279
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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Conference Report
Quantum Entanglement in the Multiverse
by Sugumi Kanno
Universe 2017, 3(2), 28; https://doi.org/10.3390/universe3020028 - 23 Mar 2017
Cited by 5 | Viewed by 5598
Abstract
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 [...] Read more.
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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