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Universe, Volume 5, Issue 6 (June 2019)

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Cover Story (view full-size image) Three zones around a black hole (BH) during accretion of a gas with a frozen magnetic field, [...] Read more.
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Open AccessArticle
Reflections on the Covariance of Modified Teleparallel Theories of Gravity
Universe 2019, 5(6), 158; https://doi.org/10.3390/universe5060158
Received: 23 May 2019 / Revised: 15 June 2019 / Accepted: 18 June 2019 / Published: 25 June 2019
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Abstract
We review the current status of the Lorentz covariance in teleparallel and modified teleparallel theories of gravity, and discuss the controversial features of the different approaches. We also revisit the issue of the remnant Lorentz gauge symmetries in f(T) gravity. [...] Read more.
We review the current status of the Lorentz covariance in teleparallel and modified teleparallel theories of gravity, and discuss the controversial features of the different approaches. We also revisit the issue of the remnant Lorentz gauge symmetries in f ( T ) gravity. Full article
(This article belongs to the Special Issue Selected Papers from Teleparallel Universes in Salamanca)
Open AccessArticle
Multiverse Predictions for Habitability: Number of Potentially Habitable Planets
Universe 2019, 5(6), 157; https://doi.org/10.3390/universe5060157
Received: 14 May 2019 / Revised: 18 June 2019 / Accepted: 21 June 2019 / Published: 25 June 2019
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Abstract
How good is our universe at making habitable planets? The answer to this depends on which factors are important for life: Does a planet need to be Earth mass? Does it need to be inside the temperate zone? are systems with hot Jupiters [...] Read more.
How good is our universe at making habitable planets? The answer to this depends on which factors are important for life: Does a planet need to be Earth mass? Does it need to be inside the temperate zone? are systems with hot Jupiters habitable? Here, we adopt different stances on the importance of each of these criteria to determine their effects on the probabilities of measuring the observed values of several physical constants. We find that the presence of planets is a generic feature throughout the multiverse, and for the most part conditioning on their particular properties does not alter our conclusions much. We find conflict with multiverse expectations if planetary size is important and it is found to be uncorrelated with stellar mass, or the mass distribution is too steep. The existence of a temperate circumstellar zone places tight lower bounds on the fine structure constant and electron to proton mass ratio. Full article
(This article belongs to the Special Issue The Multiverse)
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Open AccessArticle
Detecting the Hadron-Quark Phase Transition with Gravitational Waves
Universe 2019, 5(6), 156; https://doi.org/10.3390/universe5060156
Received: 22 May 2019 / Revised: 11 June 2019 / Accepted: 12 June 2019 / Published: 20 June 2019
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Abstract
The long-awaited detection of a gravitational wave from the merger of a binary neutron star in August 2017 (GW170817) marks the beginning of the new field of multi-messenger gravitational wave astronomy. By exploiting the extracted tidal deformations of the two neutron stars from [...] Read more.
The long-awaited detection of a gravitational wave from the merger of a binary neutron star in August 2017 (GW170817) marks the beginning of the new field of multi-messenger gravitational wave astronomy. By exploiting the extracted tidal deformations of the two neutron stars from the late inspiral phase of GW170817, it is now possible to constrain several global properties of the equation of state of neutron star matter. However, the most interesting part of the high density and temperature regime of the equation of state is solely imprinted in the post-merger gravitational wave emission from the remnant hypermassive/supramassive neutron star. This regime was not observed in GW170817, but will possibly be detected in forthcoming events within the current observing run of the LIGO/VIRGO collaboration. Numerous numerical-relativity simulations of merging neutron star binaries have been performed during the last decades, and the emitted gravitational wave profiles and the interior structure of the generated remnants have been analysed in detail. The consequences of a potential appearance of a hadron-quark phase transition in the interior region of the produced hypermassive neutron star and the evolution of its underlying matter in the phase diagram of quantum cromo dynamics will be in the focus of this article. It will be shown that the different density/temperature regions of the equation of state can be severely constrained by a measurement of the spectral properties of the emitted post-merger gravitational wave signal from a future binary compact star merger event. Full article
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Open AccessArticle
Cosmic Microwave Background from Effective Field Theory
Universe 2019, 5(6), 155; https://doi.org/10.3390/universe5060155
Received: 26 April 2019 / Revised: 6 June 2019 / Accepted: 17 June 2019 / Published: 19 June 2019
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Abstract
In this work, we study the key role of generic Effective Field Theory (EFT) framework to quantify the correlation functions in a quasi de Sitter background for an arbitrary initial choice of the quantum vacuum state. We perform the computation in unitary gauge, [...] Read more.
In this work, we study the key role of generic Effective Field Theory (EFT) framework to quantify the correlation functions in a quasi de Sitter background for an arbitrary initial choice of the quantum vacuum state. We perform the computation in unitary gauge, in which we apply the Stückelberg trick in lowest dimensional EFT operators which are broken under time diffeomorphism. In particular, using this non-linear realization of broken time diffeomorphism and truncating the action by considering the contribution from two derivative terms in the metric, we compute the two-point and three-point correlations from scalar perturbations and two-point correlation from tensor perturbations to quantify the quantum fluctuations observed in the Cosmic Microwave Background (CMB) map. We also use equilateral limit and squeezed limit configurations for the scalar three-point correlations in Fourier space. To give future predictions from EFT setup and to check the consistency of our derived results for correlations, we use the results obtained from all classes of the canonical single-field and general single-field P ( X , ϕ ) model. This analysis helps us to fix the coefficients of the relevant operators in EFT in terms of the slow-roll parameters and effective sound speed. Finally, using CMB observations from Planck we constrain all these coefficients of EFT operators for the single-field slow-roll inflationary paradigm. Full article
(This article belongs to the Special Issue The Cosmological Constant Puzzle)
Open AccessArticle
Lévy HBT Results at NA61/SHINE
Universe 2019, 5(6), 154; https://doi.org/10.3390/universe5060154
Received: 14 May 2019 / Revised: 4 June 2019 / Accepted: 14 June 2019 / Published: 16 June 2019
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Abstract
Bose–Einstein (or Hanbury–Brown and Twiss (HBT)) momentum correlations reveal the space–time structure of the particle emitting source created in high energy nucleus–nucleus collisions. In this paper we present the latest NA61/SHINE measurements of Bose–Einstein correlations of identified pion pairs and their description based [...] Read more.
Bose–Einstein (or Hanbury–Brown and Twiss (HBT)) momentum correlations reveal the space–time structure of the particle emitting source created in high energy nucleus–nucleus collisions. In this paper we present the latest NA61/SHINE measurements of Bose–Einstein correlations of identified pion pairs and their description based on Lévy distributed sources in Be + Be collisions at 150A GeV/c. We investigate the transverse mass dependence of the Lévy source parameters and discuss their possible interpretations. Full article
(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)
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Open AccessArticle
Estimating the Variation of Neutron Star Observables by Dense Symmetric Nuclear Matter Properties
Universe 2019, 5(6), 153; https://doi.org/10.3390/universe5060153
Received: 1 May 2019 / Revised: 10 June 2019 / Accepted: 12 June 2019 / Published: 14 June 2019
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Abstract
Recent multi-channel astrophysics observations and the soon-to-be published new measured electromagnetic and gravitation data provide information on the inner structure of the compact stars. These macroscopic observations can significantly increase our knowledge on the neutron star enteriors, providing constraints on the microscopic physical [...] Read more.
Recent multi-channel astrophysics observations and the soon-to-be published new measured electromagnetic and gravitation data provide information on the inner structure of the compact stars. These macroscopic observations can significantly increase our knowledge on the neutron star enteriors, providing constraints on the microscopic physical properties. On the other hand, due to the masquarade problem, there are still uncertainties on the various nuclear-matter models and their parameters as well. Calculating the properties of the dense nuclear matter, effective field theories are the most widely-used tools. However, the values of the microscopical parameters need to be set consistently to the nuclear and astrophysical measurements. In this work, we investigate how uncertainties are induced by the variation of the microscopical parameters. We use a symmetric nuclear matter in an extended σ - ω model to see the influence of the nuclear matter parameters. We calculate the dense matter equation of state and give the mass-radius diagram for a simplistic neutron star model. We present that the Landau mass and compressibility modulus of the nuclear matter have definite linear relation to the maximum mass of a Schwarzschild neutron star. Full article
(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)
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Open AccessArticle
Energy Dependent Chemical Potentials of Light Particles and Quarks from Yield Ratios of Antiparticles to Particles in High Energy Collisions
Universe 2019, 5(6), 152; https://doi.org/10.3390/universe5060152
Received: 27 April 2019 / Revised: 4 June 2019 / Accepted: 11 June 2019 / Published: 14 June 2019
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Abstract
We collect the yields of charged pions (π and π+), charged kaons (K and K+), anti-protons (p¯), and protons (p) produced in mid-rapidity interval (in most cases) in central gold–gold [...] Read more.
We collect the yields of charged pions ( π and π + ), charged kaons ( K and K + ), anti-protons ( p ¯ ), and protons (p) produced in mid-rapidity interval (in most cases) in central gold–gold (Au–Au), central lead–lead (Pb–Pb), and inelastic or non-single-diffractive proton–proton ( p p ) collisions at different collision energies. The chemical potentials of light particles and quarks are extracted from the yield ratios, π / π + , K / K + , and p ¯ / p , of antiparticles to particles over an energy range from a few GeV to above 10 TeV. At a few GeV (∼4 GeV), the chemical potentials show, and the yield ratios do not show, different trends comparing with those at other energies, although the limiting values of the chemical potentials and the yield ratios at very high energy are 0 and 1, respectively. Full article
(This article belongs to the Special Issue Heavy Ion Collisions)
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Open AccessReview
Multi-Critical Multi-Field Models: A CFT Approach to the Leading Order
Universe 2019, 5(6), 151; https://doi.org/10.3390/universe5060151
Received: 15 May 2019 / Revised: 8 June 2019 / Accepted: 11 June 2019 / Published: 13 June 2019
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Abstract
We present some general results for the multi-critical multi-field models in d>2 recently obtained using conformal field theory (CFT) and Schwinger–Dyson methods at the perturbative level without assuming any symmetry. Results in the leading non trivial order are derived consistently for [...] Read more.
We present some general results for the multi-critical multi-field models in d > 2 recently obtained using conformal field theory (CFT) and Schwinger–Dyson methods at the perturbative level without assuming any symmetry. Results in the leading non trivial order are derived consistently for several conformal data in full agreement with functional perturbative renormalization group (RG) methods. Mechanisms like emergent (possibly approximate) symmetries can be naturally investigated in this framework. Full article
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Open AccessReview
Time Reversal Symmetry in Cosmology and the Creation of a Universe–Antiuniverse Pair
Universe 2019, 5(6), 150; https://doi.org/10.3390/universe5060150
Received: 14 April 2019 / Revised: 9 June 2019 / Accepted: 12 June 2019 / Published: 13 June 2019
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Abstract
The classical evolution of the universe can be seen as a parametrised worldline of the minisuperspace, with the time variable t being the parameter that parametrises the worldline. The time reversal symmetry of the field equations implies that for any positive oriented solution [...] Read more.
The classical evolution of the universe can be seen as a parametrised worldline of the minisuperspace, with the time variable t being the parameter that parametrises the worldline. The time reversal symmetry of the field equations implies that for any positive oriented solution there can be a symmetric negative oriented one that, in terms of the same time variable, respectively represent an expanding and a contracting universe. However, the choice of the time variable induced by the correct value of the Schrödinger equation in the two universes makes it so that their physical time variables can be reversely related. In that case, the two universes would both be expanding universes from the perspective of their internal inhabitants, who identify matter with the particles that move in their spacetimes and antimatter with the particles that move in the time reversely symmetric universe. If the assumptions considered are consistent with a realistic scenario of our universe, the creation of a universe–antiuniverse pair might explain two main and related problems in cosmology: the time asymmetry and the primordial matter–antimatter asymmetry of our universe. Full article
(This article belongs to the Special Issue The Multiverse)
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Open AccessArticle
Multiverse Predictions for Habitability: The Number of Stars and Their Properties
Universe 2019, 5(6), 149; https://doi.org/10.3390/universe5060149
Received: 14 May 2019 / Revised: 7 June 2019 / Accepted: 10 June 2019 / Published: 13 June 2019
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Abstract
In a multiverse setting, we expect to be situated in a universe that is exceptionally good at producing life. Though the conditions for what life needs to arise and thrive are currently unknown, many will be tested in the coming decades. Here we [...] Read more.
In a multiverse setting, we expect to be situated in a universe that is exceptionally good at producing life. Though the conditions for what life needs to arise and thrive are currently unknown, many will be tested in the coming decades. Here we investigate several different habitability criteria, and their influence on multiverse expectations: Does complex life need photosynthesis? Is there a minimum timescale necessary for development? Can life arise on tidally locked planets? Are convective stars habitable? Variously adopting different stances on each of these criteria can alter whether our observed values of the fine structure constant, the electron to proton mass ratio, and the strength of gravity are typical to high significance. This serves as a way of generating predictions for the requirements of life that can be tested with future observations, any of which could falsify the multiverse scenario. Full article
(This article belongs to the Special Issue The Multiverse)
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Open AccessArticle
Averaging and the Shape of the Correlation Function
Universe 2019, 5(6), 148; https://doi.org/10.3390/universe5060148
Received: 30 April 2019 / Revised: 6 June 2019 / Accepted: 11 June 2019 / Published: 13 June 2019
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Abstract
A brief pedagogical introduction to correlation femtoscopy is given. We then focus on the shape of the correlation function and discuss the possible reasons for its departure from the Gaussian form and better reproduction with a Lévy stable distribution. With the help of [...] Read more.
A brief pedagogical introduction to correlation femtoscopy is given. We then focus on the shape of the correlation function and discuss the possible reasons for its departure from the Gaussian form and better reproduction with a Lévy stable distribution. With the help of Monte Carlo simulations based on asymmetric extension of the Blast-Wave model with resonances we demonstrate possible influence of averaging over many events and integrating over wide momentum bins on the shape of the correlation function. We also show that the shape is strongly influenced by the use of the one-dimensional parametrisation in the q i n v variable. Full article
(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)
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Open AccessReview
Group Field Theory Condensate Cosmology: An Appetizer
Universe 2019, 5(6), 147; https://doi.org/10.3390/universe5060147
Received: 2 April 2019 / Revised: 23 May 2019 / Accepted: 8 June 2019 / Published: 13 June 2019
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Abstract
This contribution is an appetizer to the relatively young and fast-evolving approach to quantum cosmology based on group field theory condensate states. We summarize the main assumptions and pillars of this approach which has revealed new perspectives on the long-standing question of how [...] Read more.
This contribution is an appetizer to the relatively young and fast-evolving approach to quantum cosmology based on group field theory condensate states. We summarize the main assumptions and pillars of this approach which has revealed new perspectives on the long-standing question of how to recover the continuum from discrete geometric building blocks. Among others, we give a snapshot of recent work on isotropic cosmological solutions exhibiting an accelerated expansion, a bounce where anisotropies are shown to be under control, and inhomogeneities with an approximately scale-invariant power spectrum. Finally, we point to open issues in the condensate cosmology approach. Full article
(This article belongs to the Special Issue Progress in Group Field Theory and Related Quantum Gravity Formalisms)
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Open AccessReview
Accretion into Black Hole, and Formation of Magnetically Arrested Accretion Disks
Universe 2019, 5(6), 146; https://doi.org/10.3390/universe5060146
Received: 28 March 2019 / Revised: 29 May 2019 / Accepted: 31 May 2019 / Published: 11 June 2019
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Abstract
The exact time-dependent solution is obtained for a magnetic field growth during a spherically symmetric accretion into a black hole (BH) with a Schwarzschild metric. Magnetic field is increasing with time, changing from the initially uniform into a quasi-radial field. Equipartition between magnetic [...] Read more.
The exact time-dependent solution is obtained for a magnetic field growth during a spherically symmetric accretion into a black hole (BH) with a Schwarzschild metric. Magnetic field is increasing with time, changing from the initially uniform into a quasi-radial field. Equipartition between magnetic and kinetic energies in the falling gas is supposed to be established in the developed stages of the flow. Estimates of the synchrotron radiation intensity are presented for the stationary flow. The main part of the radiation is formed in the relativistic region r 7 r g , where r g is a BH gravitational radius. The two-dimensional stationary self-similar magnetohydrodynamic solution is obtained for the matter accretion into BH, in a presence of a large-scale magnetic field, under assumption, that the magnetic field far from the BH is homogeneous and its influence on the flow is negligible. At the symmetry plane perpendicular to the direction of the distant magnetic field, the dense quasi-stationary disk is formed around BH, which structure is determined by dissipation processes. Solutions of the disk structure have been obtained for a laminar disk with Coulomb resistivity and for a turbulent disk. Parameters of the shock forming due to matter infall onto the disk are obtained. The radiation spectrum of the disk and the shock are obtained for the 10 M BH. The luminosity of such object is about the solar one, for a characteristic galactic gas density, with possibility of observation at distances less than 1 kpc. The spectra of a laminar and a turbulent disk structure around BH are very different. The laminar disk radiates mainly in the ultraviolet, the turbulent disk emits a large part of its flux in the infrared. It may occur that some of the galactic infrared star-like sources are a single BH in the turbulent accretion state. The radiative efficiency of the magnetized disk is very high, reaching 0.5 M ˙ c 2 . This model of accretion was called recently as a magnetically arrested disk (MAD). Numerical simulations of MAD and its appearance during accretion into neutron stars, are considered and discussed. Full article
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Open AccessArticle
The Sub-Eddington Boundary for the Quasar Mass–Luminosity Plane: A Theoretical Perspective
Universe 2019, 5(6), 145; https://doi.org/10.3390/universe5060145
Received: 17 May 2019 / Revised: 4 June 2019 / Accepted: 6 June 2019 / Published: 11 June 2019
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Abstract
By exploring more than sixty thousand quasars from the Sloan Digital Sky Survey Data Release 5, Steinhardt & Elvis discovered a sub-Eddington boundary and a redshift-dependent drop-off at higher black hole mass, possible clues to the growth history of massive black holes. Our [...] Read more.
By exploring more than sixty thousand quasars from the Sloan Digital Sky Survey Data Release 5, Steinhardt & Elvis discovered a sub-Eddington boundary and a redshift-dependent drop-off at higher black hole mass, possible clues to the growth history of massive black holes. Our contribution to this special issue of Universe amounts to an application of a model for black hole accretion and jet formation to these observations. For illustrative purposes, we include ~100,000 data points from the Sloan Digital Sky Survey Data Release 7 where the sub-Eddington boundary is also visible and propose a theoretical picture that explains these features. By appealing to thin disk theory and both the lower accretion efficiency and the time evolution of jetted quasars compared to non-jetted quasars in our “gap paradigm”, we explain two features of the sub-Eddington boundary. First, we show that a drop-off on the quasar mass-luminosity plane for larger black hole mass occurs at all redshifts. But the fraction of jetted quasars is directly related to the merger function in this paradigm, which means the jetted quasar fraction drops with decrease in redshift, which allows us to explain a second feature of the sub-Eddington boundary, namely a redshift dependence of the slope of the quasar mass–luminosity boundary at high black hole mass stemming from a change in radiative efficiency with time. We are able to reproduce the mass dependence of, as well as the oscillating behavior in, the slope of the sub-Eddington boundary as a function of time. The basic physical idea involves retrograde accretion occurring only for a subset of the more massive black holes, which implies that most spinning black holes in our model are prograde accretors. In short, this paper amounts to a qualitative overview of how a sub-Eddington boundary naturally emerges in the gap paradigm. Full article
(This article belongs to the Special Issue Recent Progress in Relativistic Astrophysics)
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Open AccessCommunication
Nucleosynthesis and Kilonovae from Strange Star Mergers
Universe 2019, 5(6), 144; https://doi.org/10.3390/universe5060144
Received: 27 March 2019 / Revised: 12 May 2019 / Accepted: 7 June 2019 / Published: 11 June 2019
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Abstract
In this talk, we summarize the work in progress toward a full characterization of strange star–strange star (SS–SS) mergers related to the GW/GRB/kilonova events. In addition, we show that the a priori probability constructed from the observed neutron star mass distribution points toward [...] Read more.
In this talk, we summarize the work in progress toward a full characterization of strange star–strange star (SS–SS) mergers related to the GW/GRB/kilonova events. In addition, we show that the a priori probability constructed from the observed neutron star mass distribution points toward an asymmetric binary system as the progenitor of the GW170817 event. Full article
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Open AccessCommunication
On the Gauge Fixing in the Hamiltonian Analysis of General Teleparallel Theories
Universe 2019, 5(6), 143; https://doi.org/10.3390/universe5060143
Received: 2 May 2019 / Revised: 3 June 2019 / Accepted: 5 June 2019 / Published: 10 June 2019
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Abstract
The covariant formulation of teleparallel gravity theories must include the spin connection, which has 6 degrees of freedom. One can, however, always choose a gauge such that the spin connection is put to zero. In principle this gauge may affect counting of degrees [...] Read more.
The covariant formulation of teleparallel gravity theories must include the spin connection, which has 6 degrees of freedom. One can, however, always choose a gauge such that the spin connection is put to zero. In principle this gauge may affect counting of degrees of freedom in the Hamiltonian analysis. We show for general teleparallel theories of gravity, that fixing the gauge such that the spin connection vanishes in fact does not affect the counting of degrees of freedom. This manifests in the fact that the momenta of the Lorentz transformations which generate the spin connection are fully determined by the momenta of the tetrads. Full article
(This article belongs to the Special Issue Selected Papers from Teleparallel Universes in Salamanca)
Open AccessArticle
Flat Connection for Rotating Vacuum Spacetimes in Extended Teleparallel Gravity Theories
Universe 2019, 5(6), 142; https://doi.org/10.3390/universe5060142
Received: 8 May 2019 / Revised: 3 June 2019 / Accepted: 7 June 2019 / Published: 10 June 2019
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Abstract
Teleparallel geometry utilizes Weitzenböck connection which has nontrivial torsion but no curvature and does not directly follow from the metric like Levi–Civita connection. In extended teleparallel theories, for instance in f(T) or scalar-torsion gravity, the connection must obey its antisymmetric [...] Read more.
Teleparallel geometry utilizes Weitzenböck connection which has nontrivial torsion but no curvature and does not directly follow from the metric like Levi–Civita connection. In extended teleparallel theories, for instance in f ( T ) or scalar-torsion gravity, the connection must obey its antisymmetric field equations. Thus far, only a few analytic solutions were known. In this note, we solve the f ( T , ϕ ) gravity antisymmetric vacuum field equations for a generic rotating tetrad ansatz in Weyl canonical coordinates, and find the corresponding spin connection coefficients. By a coordinate transformation, we present the solution also in Boyer–Lindquist coordinates, often used to study rotating solutions in general relativity. The result hints for the existence of another branch of rotating solutions besides the Kerr family in extended teleparallel gravities. Full article
(This article belongs to the Special Issue Selected Papers from Teleparallel Universes in Salamanca)
Open AccessArticle
General Relativity Measurements in the Field of Earth with Laser-Ranged Satellites: State of the Art and Perspectives
Universe 2019, 5(6), 141; https://doi.org/10.3390/universe5060141
Received: 18 February 2019 / Revised: 3 June 2019 / Accepted: 6 June 2019 / Published: 7 June 2019
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Abstract
Recent results of the LARASE research program in terms of model improvements and relativistic measurements are presented. In particular, the results regarding the development of new models for the non-gravitational perturbations that affect the orbit of the LAGEOS and LARES satellites are described [...] Read more.
Recent results of the LARASE research program in terms of model improvements and relativistic measurements are presented. In particular, the results regarding the development of new models for the non-gravitational perturbations that affect the orbit of the LAGEOS and LARES satellites are described and discussed. These are subtle and complex effects that need a deep knowledge of the structure and the physical characteristics of the satellites in order to be correctly accounted for. In the field of gravitational measurements, we present a new measurement of the relativistic Lense-Thirring precession with a 0.5 % precision. In this measurement, together with the relativistic effect we also estimated two even zonal harmonics coefficients. The uncertainties of the even zonal harmonics of the gravitational field of the Earth have been responsible, until now, of the larger systematic uncertainty in the error budget of this kind of measurements. For this reason, the role of the errors related to the model used for the gravitational field of the Earth in these measurements is discussed. In particular, emphasis is given to GRACE temporal models, that strongly help to reduce this kind of systematic errors. Full article
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Open AccessReview
Latest Results from RHIC + Progress on Determining q ^ L in RHI Collisions Using Di-Hadron Correlations
Universe 2019, 5(6), 140; https://doi.org/10.3390/universe5060140
Received: 15 April 2019 / Revised: 10 May 2019 / Accepted: 24 May 2019 / Published: 5 June 2019
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Abstract
Results from Relativistic Heavy Ion Collider Physics in 2018 and plans for the future at Brookhaven National Laboratory are presented. Full article
(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)
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Open AccessCommunication
Gauge Structure of Teleparallel Gravity
Universe 2019, 5(6), 139; https://doi.org/10.3390/universe5060139
Received: 23 April 2019 / Revised: 30 May 2019 / Accepted: 1 June 2019 / Published: 5 June 2019
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Abstract
During the conference Teleparallel Universes in Salamanca, we became aware of a recent paper [M. Fontanini, E. Huguet, and M. Le Delliou, Phys. Rev. D 2019, 99, 064006] in which some criticisms on the interpretation of teleparallel gravity as a gauge [...] Read more.
During the conference Teleparallel Universes in Salamanca, we became aware of a recent paper [M. Fontanini, E. Huguet, and M. Le Delliou, Phys. Rev. D 2019, 99, 064006] in which some criticisms on the interpretation of teleparallel gravity as a gauge theory for the translation group were put forward. This triggered a discussion about the arguments on which those criticisms were based, whose output is described in the present paper. The main conclusion is that to a great extent, those arguments are incorrect, and lack mathematical and physical support. Full article
(This article belongs to the Special Issue Selected Papers from Teleparallel Universes in Salamanca)
Open AccessArticle
The Effective Field Theory of Dark Energy Diagnostic of Linear Horndeski Theories After GW170817 and GRB170817A
Universe 2019, 5(6), 138; https://doi.org/10.3390/universe5060138
Received: 2 May 2019 / Revised: 29 May 2019 / Accepted: 31 May 2019 / Published: 4 June 2019
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Abstract
We summarize the effective field theory of dark energy construction to explore observable predictions of linear Horndeski theories. We review the diagnostic of these theories on the correlation of the large-scale structure phenomenological functions: the effective Newton constant, the light deflection parameter, and [...] Read more.
We summarize the effective field theory of dark energy construction to explore observable predictions of linear Horndeski theories. We review the diagnostic of these theories on the correlation of the large-scale structure phenomenological functions: the effective Newton constant, the light deflection parameter, and the growth function of matter perturbations. We take this opportunity to discuss the evolution of the bounds the propagation speed of gravitational waves has undergone and use the most restrictive one to update the diagnostic. Full article
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Open AccessReview
Observing the Dark Sector
Universe 2019, 5(6), 137; https://doi.org/10.3390/universe5060137
Received: 10 April 2019 / Revised: 20 May 2019 / Accepted: 24 May 2019 / Published: 4 June 2019
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Abstract
Despite the observational success of the standard model of cosmology, present-day observations do not tightly constrain the nature of dark matter and dark energy and modifications to the theory of general relativity. Here, we will discuss some of the ongoing and upcoming surveys [...] Read more.
Despite the observational success of the standard model of cosmology, present-day observations do not tightly constrain the nature of dark matter and dark energy and modifications to the theory of general relativity. Here, we will discuss some of the ongoing and upcoming surveys that will revolutionize our understanding of the dark sector. Full article
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Open AccessCommunication
The Structure of the Hadron-Quark Combustion Zone
Universe 2019, 5(6), 136; https://doi.org/10.3390/universe5060136
Received: 8 May 2019 / Revised: 30 May 2019 / Accepted: 3 June 2019 / Published: 4 June 2019
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Abstract
Hadron-quark combustion in dense matter is a central topic in the study of phases in compact stars and their high-energy astrophysics. We critically reviewed the literature on hadron-quark combustion, dividing them into a “first wave” that treats the problem as a steady-state burning [...] Read more.
Hadron-quark combustion in dense matter is a central topic in the study of phases in compact stars and their high-energy astrophysics. We critically reviewed the literature on hadron-quark combustion, dividing them into a “first wave” that treats the problem as a steady-state burning with or without constraints of mechanical equilibrium, and a “second wave” which uses numerical techniques to resolve the burning front and solves the underlying partial differential equations for the chemistry of the burning front under less restrictive conditions. We detailed the inaccuracies that the second wave amends over the first wave and highlight crucial differences between various approaches in the second wave. We also include results from time-dependent simulations of the reaction zone that include a hadronic EOS, neutrinos, and self-consistent thermodynamics without using parameterized shortcuts. Full article
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Open AccessArticle
Quaternion Electromagnetism and the Relation with Two-Spinor Formalism
Universe 2019, 5(6), 135; https://doi.org/10.3390/universe5060135
Received: 26 April 2019 / Revised: 27 May 2019 / Accepted: 28 May 2019 / Published: 3 June 2019
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Abstract
By using complex quaternion, which is the system of quaternion representation extended to complex numbers, we show that the laws of electromagnetism can be expressed much more simply and concisely. We also derive the quaternion representation of rotations and boosts from the spinor [...] Read more.
By using complex quaternion, which is the system of quaternion representation extended to complex numbers, we show that the laws of electromagnetism can be expressed much more simply and concisely. We also derive the quaternion representation of rotations and boosts from the spinor representation of Lorentz group. It is suggested that the imaginary “i” should be attached to the spatial coordinates, and observe that the complex conjugate of quaternion representation is exactly equal to parity inversion of all physical quantities in the quaternion. We also show that using quaternion is directly linked to the two-spinor formalism. Finally, we discuss meanings of quaternion, octonion and sedenion in physics as n-fold rotation. Full article
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Open AccessCommunication
Multiplicity Dependence in the Non-Extensive Hadronization Model Calculated by the HIJING++ Framework
Universe 2019, 5(6), 134; https://doi.org/10.3390/universe5060134
Received: 30 April 2019 / Revised: 22 May 2019 / Accepted: 23 May 2019 / Published: 1 June 2019
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Abstract
The non-extensive statistical description of the identified final state particles measured in high energy collisions is well-known by its wide range of applicability. However, there are many open questions that need to be answered, including but not limited to, the question of the [...] Read more.
The non-extensive statistical description of the identified final state particles measured in high energy collisions is well-known by its wide range of applicability. However, there are many open questions that need to be answered, including but not limited to, the question of the observed mass scaling of massive hadrons or the size and multiplicity dependence of the model parameters. This latter is especially relevant, since currently the amount of available experimental data with high multiplicity at small systems is very limited. This contribution has two main goals: On the one hand we provide a status report of the ongoing tuning of the soon-to-be-released HIJING++ Monte Carlo event generator. On the other hand, the role of multiplicity dependence of the parameters in the non-extensive hadronization model is investigated with HIJING++ calculations. We present cross-check comparisons of HIJING++ with existing experimental data to verify its validity in our range of interest as well as calculations at high-multiplicity regions where we have insufficient experimental data. Full article
(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)
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Open AccessArticle
Coulomb Final State Interaction in Heavy Ion Collisions for Lévy Sources
Universe 2019, 5(6), 133; https://doi.org/10.3390/universe5060133
Received: 17 April 2019 / Revised: 23 May 2019 / Accepted: 23 May 2019 / Published: 28 May 2019
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Abstract
Investigation of momentum space correlations of particles produced in high energy reactions requires taking final state interactions into account, a crucial point of any such analysis. Coulomb interaction between charged particles is the most important such effect. In small systems like those created [...] Read more.
Investigation of momentum space correlations of particles produced in high energy reactions requires taking final state interactions into account, a crucial point of any such analysis. Coulomb interaction between charged particles is the most important such effect. In small systems like those created in e + e - - or p + p collisions, the so-called Gamow factor (valid for a point-like particle source) gives an acceptable description of the Coulomb interaction. However, in larger systems such as central or mid-central heavy ion collisions, more involved approaches are needed. In this paper we investigate the Coulomb final state interaction for Lévy-type source functions that were recently shown to be of much interest for a refined description of the space-time picture of particle production in heavy-ion collisions. Full article
(This article belongs to the Special Issue The Zimányi School and Analytic Hydrodynamics in High Energy Physics)
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