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Universe, Volume 5, Issue 10 (October 2019)

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Open AccessReview
An Introduction to Particle Dark Matter
Universe 2019, 5(10), 213; https://doi.org/10.3390/universe5100213 - 17 Oct 2019
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Abstract
We review the features of Dark Matter as a particle, presenting some old and new instructive models, and looking for their physical implications in the early universe and in the process of structure formation. We also present a schematic of Dark Matter searches [...] Read more.
We review the features of Dark Matter as a particle, presenting some old and new instructive models, and looking for their physical implications in the early universe and in the process of structure formation. We also present a schematic of Dark Matter searches and introduce the most promising candidates to the role of Dark Matter particle. Full article
Open AccessArticle
Conceptual Challenges on the Road to the Multiverse
Universe 2019, 5(10), 212; https://doi.org/10.3390/universe5100212 - 10 Oct 2019
Viewed by 145
Abstract
The current debate about a possible change of paradigm from a single universe to a multiverse scenario could have deep implications on our view of cosmology and of science in general. These implications therefore deserve to be analyzed from a fundamental conceptual level. [...] Read more.
The current debate about a possible change of paradigm from a single universe to a multiverse scenario could have deep implications on our view of cosmology and of science in general. These implications therefore deserve to be analyzed from a fundamental conceptual level. We briefly review the different multiverse ideas, both historically and within contemporary physics. We then discuss several positions within philosophy of science with regard to scientific progress, and apply these to the multiverse debate. Finally, we construct some key concepts for a physical multiverse scenario and discuss the challenges this scenario has to deal with in order to provide a solid, testable theory. Full article
(This article belongs to the Special Issue The Multiverse)
Open AccessReview
Holographic Entanglement in Group Field Theory
Universe 2019, 5(10), 211; https://doi.org/10.3390/universe5100211 - 09 Oct 2019
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Abstract
This work is meant as a review summary of a series of recent results concerning the derivation of a holographic entanglement entropy formula for generic open spin network states in the group field theory (GFT) approach to quantum gravity. The statistical group-field computation [...] Read more.
This work is meant as a review summary of a series of recent results concerning the derivation of a holographic entanglement entropy formula for generic open spin network states in the group field theory (GFT) approach to quantum gravity. The statistical group-field computation of the Rényi entropy for a bipartite network state for a simple interacting GFT is reviewed, within a recently proposed dictionary between group field theories and random tensor networks, and with an emphasis on the problem of a consistent characterisation of the entanglement entropy in the GFT second quantisation formalism. Full article
(This article belongs to the Special Issue Progress in Group Field Theory and Related Quantum Gravity Formalisms)
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Open AccessCommunication
Study of Very Forward Neutrons with the CMS Zero Degree Calorimeter
Universe 2019, 5(10), 210; https://doi.org/10.3390/universe5100210 - 09 Oct 2019
Viewed by 111
Abstract
Forward neutrons are studied in proton-lead collisions at the CMS experiment at the CERN LHC. They provide information on the centrality and event plane of collisions and provide an opportunity to study nuclear breakup. At the CMS experiment they are detected by the [...] Read more.
Forward neutrons are studied in proton-lead collisions at the CMS experiment at the CERN LHC. They provide information on the centrality and event plane of collisions and provide an opportunity to study nuclear breakup. At the CMS experiment they are detected by the Zero Degree Calorimeters (ZDCs) in the | η | > 8.5 pseudorapidity range. The ZDCs are quartz fiber Cherenkov calorimeters using tungsten as absorber. Test beam data and events with a single spectator neutron are used for the calibration of these detectors. A Fourier-based method is used correct for the effect of multiple pPb collisions. The corrected ZDC energy distribution is used to calculate centrality percentiles and unfold the neutron multiplicity distribution. 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
Tripartite Entanglement: Foundations and Applications
Universe 2019, 5(10), 209; https://doi.org/10.3390/universe5100209 - 09 Oct 2019
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Abstract
We review some current ideas of tripartite entanglement. In particular, we consider the case representing the next level of complexity beyond the simplest (though far from trivial) one, namely the bipartite case. This kind of entanglement plays an essential role in understanding the [...] Read more.
We review some current ideas of tripartite entanglement. In particular, we consider the case representing the next level of complexity beyond the simplest (though far from trivial) one, namely the bipartite case. This kind of entanglement plays an essential role in understanding the foundations of quantum mechanics. It also allows for implementing several applications in the fields of quantum information processing and quantum computing. In this paper, we review the fundamental aspects of tripartite entanglement focusing on Greenberger–Horne–Zeilinger and W states for discrete variables. We discuss the possibility of using it as a resource to execute quantum protocols and present some examples in detail. Full article
(This article belongs to the Special Issue Quantum Dynamics and Applications)
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Open AccessArticle
Temperature Dependence of the Axion Mass in a Scenario Where the Restoration of Chiral Symmetry Drives the Restoration of the UA(1) Symmetry
Universe 2019, 5(10), 208; https://doi.org/10.3390/universe5100208 - 08 Oct 2019
Viewed by 107
Abstract
The temperature (T) dependence of the axion mass is predicted for T s up to 2.3 × the chiral restoration temperature of QCD. The axion is related to the U A ( 1 ) anomaly. The squared axion mass [...] Read more.
The temperature (T) dependence of the axion mass is predicted for T s up to 2.3 × the chiral restoration temperature of QCD. The axion is related to the U A ( 1 ) anomaly. The squared axion mass m a ( T ) 2 is, modulo the presently undetermined scale of spontaneous breaking of Peccei–Quinn symmetry f a (squared), equal to QCD topological susceptibility χ ( T ) for all T. We obtain χ ( T ) by using quark condensates calculated in two effective Dyson–Schwinger models of nonperturbative QCD. They exhibit the correct chiral behavior, including the dynamical breaking of chiral symmetry and its restoration at high T. This is reflected in the U A ( 1 ) symmetry breaking and restoration through χ ( T ) . In our previous studies, such χ ( T ) yields the T-dependence of the U A ( 1 ) -anomaly-influenced masses of η and η mesons consistent with experiment. This in turn supports our prediction for the T-dependence of the axion mass. Another support is a rather good agreement with the pertinent lattice results. This agreement is not spoiled by our varying u and d quark mass parameters out of the isospin limit. 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
Driving Interactions Efficiently in a Composite Few-Body System
Universe 2019, 5(10), 207; https://doi.org/10.3390/universe5100207 - 07 Oct 2019
Viewed by 162
Abstract
We study how to efficiently control an interacting few-body system consisting of three harmonically trapped bosons. Specifically, we investigate the process of modulating the inter-particle interactions to drive an initially non-interacting state to a strongly interacting one, which is an eigenstate of a [...] Read more.
We study how to efficiently control an interacting few-body system consisting of three harmonically trapped bosons. Specifically, we investigate the process of modulating the inter-particle interactions to drive an initially non-interacting state to a strongly interacting one, which is an eigenstate of a chosen Hamiltonian. We also show that for unbalanced subsystems, where one can individually control the different inter- and intra-species interactions, complex dynamics originate when the symmetry of the ground state is broken by phase separation. However, as driving the dynamics too quickly can result in unwanted excitations of the final state, we optimize the driven processes using shortcuts to adiabaticity, which are designed to reduce these excitations at the end of the interaction ramp, ensuring that the target eigenstate is reached. Full article
(This article belongs to the Special Issue Quantum Dynamics and Applications)
Open AccessReview
On the Mathematics of Coframe Formalism and Einstein–Cartan Theory—A Brief Review
Universe 2019, 5(10), 206; https://doi.org/10.3390/universe5100206 - 27 Sep 2019
Viewed by 191
Abstract
This article is a review of what could be considered the basic mathematics of Einstein–Cartan theory. We discuss the formalism of principal bundles, principal connections, curvature forms, gauge fields, torsion form, and Bianchi identities, and eventually, we will end up with Einstein–Cartan–Sciama–Kibble field [...] Read more.
This article is a review of what could be considered the basic mathematics of Einstein–Cartan theory. We discuss the formalism of principal bundles, principal connections, curvature forms, gauge fields, torsion form, and Bianchi identities, and eventually, we will end up with Einstein–Cartan–Sciama–Kibble field equations and conservation laws in their implicit formulation. Full article
(This article belongs to the Special Issue Torsion-Gravity and Spinors in Fundamental Theoretical Physics)
Open AccessArticle
Dynamics of Electromagnetic Fields and Structure of Regular Rotating Electrically Charged Black Holes and Solitons in Nonlinear Electrodynamics Minimally Coupled to Gravity
Universe 2019, 5(10), 205; https://doi.org/10.3390/universe5100205 - 27 Sep 2019
Viewed by 163
Abstract
We study the dynamics of electromagnetic fields of regular rotating electrically charged black holes and solitons replacing naked singularities in nonlinear electrodynamics minimally coupled to gravity (NED-GR). They are related by electromagnetic and gravitational interactions and described by the axially symmetric NED-GR solutions [...] Read more.
We study the dynamics of electromagnetic fields of regular rotating electrically charged black holes and solitons replacing naked singularities in nonlinear electrodynamics minimally coupled to gravity (NED-GR). They are related by electromagnetic and gravitational interactions and described by the axially symmetric NED-GR solutions asymptotically Kerr-Newman for a distant observer. Geometry is described by the metrics of the Kerr-Schild class specified by T t t = T r r ( p r = ρ ) in the co-rotating frame. All regular axially symmetric solutions obtained from spherical solutions with the Newman-Janis algorithm belong to this class. The basic generic feature of all regular objects of this class, both electrically charged and electrically neutral, is the existence of two kinds of de Sitter vacuum interiors. We analyze the regular solutions to dynamical equations for electromagnetic fields and show which kind of a regular interior is favored by electromagnetic dynamics for NED-GR objects. Full article
(This article belongs to the Special Issue Rotation Effects in Relativity)
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Open AccessArticle
Constraints on Microscopic and Phenomenological Equations of State of Dense Matter from GW170817
Universe 2019, 5(10), 204; https://doi.org/10.3390/universe5100204 - 25 Sep 2019
Viewed by 216
Abstract
We discuss the constraints on the equation of state (EOS) of neutron star matter obtained by the data analysis of the neutron star-neutron star merger in the event GW170807. To this scope, we consider two recent microscopic EOS models computed starting from two-body [...] Read more.
We discuss the constraints on the equation of state (EOS) of neutron star matter obtained by the data analysis of the neutron star-neutron star merger in the event GW170807. To this scope, we consider two recent microscopic EOS models computed starting from two-body and three-body nuclear interactions derived using chiral perturbation theory. For comparison, we also use three representative phenomenological EOS models derived within the relativistic mean field approach. For each model, we determine the β -stable EOS and then the corresponding neutron star structure by solving the equations of hydrostatic equilibrium in general relativity. In addition, we calculate the tidal deformability parameters for the two neutron stars and discuss the results of our calculations in connection with the constraints obtained from the gravitational wave signal in GW170817. We find that the tidal deformabilities and radii for the binary’s component neutron stars in GW170817, calculated using a recent microscopic EOS model proposed by the present authors, are in very good agreement with those derived by gravitational waves data. Full article
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Open AccessArticle
Flavour Composition and Entropy Increase of Cosmological Neutrinos After Decoherence
Universe 2019, 5(10), 203; https://doi.org/10.3390/universe5100203 - 25 Sep 2019
Viewed by 140
Abstract
We propose that gravitational interactions of cosmic neutrinos with the statistically homogeneous and isotropic fluctuations of space-time lead to decoherence. This working hypothesis, which we describe by means of a Lindblad operator, is applied to the system of two- and three-flavour neutrinos undergoing [...] Read more.
We propose that gravitational interactions of cosmic neutrinos with the statistically homogeneous and isotropic fluctuations of space-time lead to decoherence. This working hypothesis, which we describe by means of a Lindblad operator, is applied to the system of two- and three-flavour neutrinos undergoing vacuum oscillations and the consequences are investigated. As a result of this decoherence we find that the neutrino entropy would increase as a function of initial spectral distortions, mixing angles and charge-parity (CP)-violation phase. Subsequently we discuss the chances to discover such an increase observationally (in principle). We also present the expected flavour composition of the cosmic neutrino background after decoherence is completed. The physics of two- or three-flavour oscillation of cosmological neutrinos resembles in many aspects two- or three-level systems in atomic clocks, which were recently proposed by Weinberg for the study of decoherence phenomena. Full article
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