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Universe, Volume 4, Issue 12 (December 2018)

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Cover Story (view full-size image) Wormholes are shortcuts connecting two regions of spacetime that would otherwise be distant. We [...] Read more.
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Open AccessArticle Primordial Power Spectra from an Emergent Universe: Basic Results and Clarifications
Universe 2018, 4(12), 149; https://doi.org/10.3390/universe4120149
Received: 30 November 2018 / Revised: 13 December 2018 / Accepted: 15 December 2018 / Published: 18 December 2018
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Abstract
Emergent cosmological models, together with the Big Bang and bouncing scenarios, are among the possible descriptions of the early Universe. This work aims at clarifying some general features of the primordial tensor power spectrum in this specific framework. In particular, some naive beliefs
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Emergent cosmological models, together with the Big Bang and bouncing scenarios, are among the possible descriptions of the early Universe. This work aims at clarifying some general features of the primordial tensor power spectrum in this specific framework. In particular, some naive beliefs are corrected. Using a toy model, we investigate the conditions required to produce a scale-invariant spectrum and show to what extent this spectrum can exhibit local features sensitive to the details of the scale factor evolution near the transition time. 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 Precision Determination of αs from Lattice QCD
Universe 2018, 4(12), 148; https://doi.org/10.3390/universe4120148
Received: 28 November 2018 / Revised: 12 December 2018 / Accepted: 13 December 2018 / Published: 15 December 2018
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Abstract
We present an overview of the recent lattice determination of the QCD coupling αs by the ALPHA Collaboration. The computation is based on the non-perturbative determination of the Λ-parameter of Nf=3 QCD, and the perturbative matching of the
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We present an overview of the recent lattice determination of the QCD coupling α s by the ALPHA Collaboration. The computation is based on the non-perturbative determination of the Λ-parameter of Nf = 3 QCD, and the perturbative matching of the Nf = 3 and Nf = 5 theories. The final result: α s ( m Z ) = 0.11852 ( 84 ) , reaches sub-percent accuracy. Full article
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Open AccessConference Report Recent Developments and Results on Double Beta Decays with Crystal Scintillators and HPGe Spectrometry
Universe 2018, 4(12), 147; https://doi.org/10.3390/universe4120147
Received: 3 November 2018 / Revised: 3 December 2018 / Accepted: 6 December 2018 / Published: 14 December 2018
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Abstract
Recent developments, results, and perspectives arising from double beta decay experiments at the Gran Sasso National Laboratory (LNGS) of the INFN by using HPGe detectors and crystal scintillators and by exploiting various approaches and different isotopes are summarized. The measurements here presented have
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Recent developments, results, and perspectives arising from double beta decay experiments at the Gran Sasso National Laboratory (LNGS) of the INFN by using HPGe detectors and crystal scintillators and by exploiting various approaches and different isotopes are summarized. The measurements here presented have been performed in the experimental set-ups of the DAMA collaboration. These setups are optimized for low-background studies and operate deep underground at LNGS. The presented results are of significant value to the field, and the sensitivity achieved for some of the considered isotopes is one of the best available to date. Full article
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Open AccessReview Momentum Space Topology and Non-Dissipative Currents
Universe 2018, 4(12), 146; https://doi.org/10.3390/universe4120146
Received: 6 November 2018 / Revised: 6 December 2018 / Accepted: 7 December 2018 / Published: 12 December 2018
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Abstract
Relativistic heavy ion collisions represent an arena for the probe of various anomalous transport effects. Those effects, in turn, reveal the correspondence between the solid state physics and the high energy physics, which share the common formalism of quantum field theory. It may
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Relativistic heavy ion collisions represent an arena for the probe of various anomalous transport effects. Those effects, in turn, reveal the correspondence between the solid state physics and the high energy physics, which share the common formalism of quantum field theory. It may be shown that for the wide range of field–theoretic models, the response of various nondissipative currents to the external gauge fields is determined by the momentum space topological invariants. Thus, the anomalous transport appears to be related to the investigation of momentum space topology—the approach developed earlier mainly in the condensed matter theory. Within this methodology we analyse systematically the anomalous transport phenomena, which include, in particular, the anomalous quantum Hall effect, the chiral separation effect, the chiral magnetic effect, the chiral vortical effect and the rotational Hall effect. Full article
Open AccessArticle Prospects for Heavy-Ion Physics with the MPD Detector at NICA
Universe 2018, 4(12), 145; https://doi.org/10.3390/universe4120145
Received: 22 November 2018 / Revised: 5 December 2018 / Accepted: 6 December 2018 / Published: 8 December 2018
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Abstract
The construction of the NICA accelerator facility is underway at Joint Institute for Nuclear Research (JINR) (Dubna, Russia). The main goal of the MPD experiment at NICA will be the experimental exploration of the Quantum Chromodynamics (QCD) phase structure at high baryon density.
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The construction of the NICA accelerator facility is underway at Joint Institute for Nuclear Research (JINR) (Dubna, Russia). The main goal of the MPD experiment at NICA will be the experimental exploration of the Quantum Chromodynamics (QCD) phase structure at high baryon density. In this article, the current status of the NICA/MPD project is presented. Full article
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Open AccessArticle Kappa Distributions: Statistical Physics and Thermodynamics of Space and Astrophysical Plasmas
Universe 2018, 4(12), 144; https://doi.org/10.3390/universe4120144
Received: 11 October 2018 / Revised: 4 December 2018 / Accepted: 5 December 2018 / Published: 7 December 2018
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Abstract
Kappa distributions received impetus as they provide efficient modelling of the observed particle distributions in space and astrophysical plasmas throughout the heliosphere. This paper presents (i) the connection of kappa distributions with statistical mechanics, by maximizing the associated q-entropy under the constraints
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Kappa distributions received impetus as they provide efficient modelling of the observed particle distributions in space and astrophysical plasmas throughout the heliosphere. This paper presents (i) the connection of kappa distributions with statistical mechanics, by maximizing the associated q-entropy under the constraints of the canonical ensemble within the framework of continuous description; (ii) the derivation of q-entropy from first principles that characterize space plasmas, the additivity of energy, and entropy; and (iii) the derivation of the characteristic first order differential equation, whose solution is the kappa distribution function. Full article
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Open AccessReview Results from the OPERA Experiment in the CNGS Beam
Universe 2018, 4(12), 143; https://doi.org/10.3390/universe4120143
Received: 31 October 2018 / Revised: 28 November 2018 / Accepted: 3 December 2018 / Published: 7 December 2018
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Abstract
The OPERA experiment was designed to observe νμντ oscillations through τ appearance on the CERN Neutrino to Gran Sasso (CNGS) beam over a baseline of 730 km. OPERA was a hybrid experiment composed of lead plates and emulsion layers
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The OPERA experiment was designed to observe ν μ ν τ oscillations through τ appearance on the CERN Neutrino to Gran Sasso (CNGS) beam over a baseline of 730 km. OPERA was a hybrid experiment composed of lead plates and emulsion layers acting as a target for neutrino interactions. The experiment was complemented with electronic detectors: scintillator strips used as Target Trackers and muon spectrometers. A review of the OPERA final results is presented in this paper. Full article
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Open AccessConference Report Exotic Baryons in Chiral Soliton Models
Universe 2018, 4(12), 142; https://doi.org/10.3390/universe4120142
Received: 29 October 2018 / Revised: 28 November 2018 / Accepted: 29 November 2018 / Published: 6 December 2018
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Abstract
We cautiously review the treatment of pentaquark exotic baryons in chiral soliton models. We consider two examples and argue that any consistent and self-contained description must go beyond the mean field approximation that only considers the classical soliton and the canonical quantization of
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We cautiously review the treatment of pentaquark exotic baryons in chiral soliton models. We consider two examples and argue that any consistent and self-contained description must go beyond the mean field approximation that only considers the classical soliton and the canonical quantization of its (would-be) zero modes via collective coordinates. Full article
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Open AccessConference Report Spontaneous μ-τ Reflection Symmetry Breaking in Neutrino Phenomenology
Universe 2018, 4(12), 141; https://doi.org/10.3390/universe4120141
Received: 15 November 2018 / Accepted: 30 November 2018 / Published: 4 December 2018
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Abstract
The latest global analysis of neutrino oscillation data indicates that the normal neutrino mass ordering is favored over the inverted one at the 3σ level. The best-fit values of the largest neutrino mixing angle θ23 and the Dirac CP-violating phase δ
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The latest global analysis of neutrino oscillation data indicates that the normal neutrino mass ordering is favored over the inverted one at the 3 σ level. The best-fit values of the largest neutrino mixing angle θ 23 and the Dirac CP-violating phase δ are located in the higher octant and the third quadrant, respectively. We show that these experimental trends can be naturally explained by the μ - τ reflection symmetry breaking, triggered by the one-loop renormalization-group equations (RGEs) running from a superhigh energy scale down to the electroweak scale in the framework of the minimal supersymmetric standard model (MSSM). The complete parameter space is numerically explored for both the Majorana and Dirac cases, by allowing the smallest neutrino mass m 1 and the MSSM parameter tan β to vary within their reasonable ranges. Full article
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Open AccessArticle Regular Solutions in Higher-Derivative Gravity
Universe 2018, 4(12), 140; https://doi.org/10.3390/universe4120140
Received: 31 October 2018 / Revised: 27 November 2018 / Accepted: 29 November 2018 / Published: 2 December 2018
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Abstract
Local gravitational theories with more than four derivatives can have remarkable quantum properties. Namely, they can be super-renormalizable and may be unitary in the Lee-Wick sense, if the massive poles of the propagator are complex. It is important, therefore, to also explore the
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Local gravitational theories with more than four derivatives can have remarkable quantum properties. Namely, they can be super-renormalizable and may be unitary in the Lee-Wick sense, if the massive poles of the propagator are complex. It is important, therefore, to also explore the classical aspects of these theories. In this talk we present recent results in this direction. Specifically, we discuss the effect that that higher-order terms can have on the Newtonian potential and related singularities. Full article
Open AccessArticle Rainbow-Like Black-Hole Metric from Loop Quantum Gravity
Universe 2018, 4(12), 139; https://doi.org/10.3390/universe4120139
Received: 18 October 2018 / Revised: 28 November 2018 / Accepted: 28 November 2018 / Published: 1 December 2018
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Abstract
Hypersurface deformation algebra consists of a fruitful approach to derive deformed solutions of general relativity based on symmetry considerations with quantum-gravity effects, of which the linearization has been recently demonstrated to be connected to the DSR program by κ-Poincaré symmetry. Based on
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Hypersurface deformation algebra consists of a fruitful approach to derive deformed solutions of general relativity based on symmetry considerations with quantum-gravity effects, of which the linearization has been recently demonstrated to be connected to the DSR program by κ -Poincaré symmetry. Based on this approach, we analyzed the solution derived for the interior of a black hole and we found similarities with the so-called rainbow metrics, like a momentum-dependence of the metric functions. Moreover, we derived an effective, time-dependent Planck length and compared different regularization schemes. Full article
(This article belongs to the Special Issue Progress in Group Field Theory and Related Quantum Gravity Formalisms)
Open AccessArticle (q, σ, τ)-Differential Graded Algebras
Universe 2018, 4(12), 138; https://doi.org/10.3390/universe4120138
Received: 30 October 2018 / Revised: 23 November 2018 / Accepted: 23 November 2018 / Published: 1 December 2018
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Abstract
We propose the notion of (q,σ,τ)-differential graded algebra, which generalizes the notions of (σ,τ)-differential graded algebra and q-differential graded algebra. We construct two examples of (q,σ,
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We propose the notion of ( q , σ , τ ) -differential graded algebra, which generalizes the notions of ( σ , τ ) -differential graded algebra and q-differential graded algebra. We construct two examples of ( q , σ , τ ) -differential graded algebra, where the first one is constructed by means of the generalized Clifford algebra with two generators (reduced quantum plane), where we use a ( σ , τ ) -twisted graded q-commutator. In order to construct the second example, we introduce the notion of ( σ , τ ) -pre-cosimplicial algebra. Full article
Open AccessArticle Light Propagation through Nanophotonics Wormholes
Universe 2018, 4(12), 137; https://doi.org/10.3390/universe4120137
Received: 6 November 2018 / Revised: 26 November 2018 / Accepted: 27 November 2018 / Published: 29 November 2018
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Abstract
We consider the propagation of light along a 3D nanophotonic structure with the spatial shape of a spacetime containing a traversable wormhole. We show that waves experience significant changes of phase and group velocities when propagating along this curved space. This experiment can
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We consider the propagation of light along a 3D nanophotonic structure with the spatial shape of a spacetime containing a traversable wormhole. We show that waves experience significant changes of phase and group velocities when propagating along this curved space. This experiment can be realized with state-of-the-art nanophotonics technology. Full article
(This article belongs to the Special Issue Wormholes in Space-Time: Theory and Facts)
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Open AccessConference Report Degravitation and the Cascading DGP Model
Universe 2018, 4(12), 136; https://doi.org/10.3390/universe4120136
Received: 2 November 2018 / Revised: 25 November 2018 / Accepted: 26 November 2018 / Published: 29 November 2018
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Abstract
We consider the 6D Cascading DGP model, a braneworld model which is a promising candidate to realize the phenomenon of the degravitation of vacuum energy. Focusing on a recently proposed thin limit description of the model, we study solutions where the induced metric
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We consider the 6D Cascading DGP model, a braneworld model which is a promising candidate to realize the phenomenon of the degravitation of vacuum energy. Focusing on a recently proposed thin limit description of the model, we study solutions where the induced metric on the codimension-2 brane is of the de Sitter form. While these solutions have already been recovered in the literature imposing by hand the bulk to be flat, we show that it is possible to derive them without making this assumption, by solving a suitably chosen subset of the bulk equations. Full article
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Open AccessArticle Analogies between the Black Hole Interior and the Type II Weyl Semimetals
Universe 2018, 4(12), 135; https://doi.org/10.3390/universe4120135
Received: 7 November 2018 / Revised: 19 November 2018 / Accepted: 22 November 2018 / Published: 28 November 2018
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Abstract
In the Painleve–Gullstrand (PG) reference frame, the description of elementary particles in the background of a black hole (BH) is similar to the description of non-relativistic matter falling toward the BH center. The velocity of the fall depends on the distance to the
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In the Painleve–Gullstrand (PG) reference frame, the description of elementary particles in the background of a black hole (BH) is similar to the description of non-relativistic matter falling toward the BH center. The velocity of the fall depends on the distance to the center, and it surpasses the speed of light inside the horizon. Another analogy to non-relativistic physics appears in the description of the massless fermionic particle. Its Hamiltonian inside the BH, when written in the PG reference frame, is identical to the Hamiltonian of the electronic quasiparticles in type II Weyl semimetals (WSII) that reside in the vicinity of a type II Weyl point. When these materials are in the equilibrium state, the type II Weyl point becomes the crossing point of the two pieces of the Fermi surface called Fermi pockets. It was previously stated that there should be a Fermi surface inside a black hole in equilibrium. In real materials, type II Weyl points come in pairs, and the descriptions of the quasiparticles in their vicinities are, to a certain extent, inverse. Namely, the directions of their velocities are opposite. In line with the mentioned analogy, we propose the hypothesis that inside the equilibrium BH there exist low-energy excitations moving toward the exterior of the BH. These excitations are able to escape from the BH, unlike ordinary matter that falls to its center. The important consequences to the quantum theory of black holes follow. Full article
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Open AccessConference Report Large High-Efficiency Thermal Neutron Detectors Based on the Micromegas Technology
Universe 2018, 4(12), 134; https://doi.org/10.3390/universe4120134
Received: 22 October 2018 / Revised: 20 November 2018 / Accepted: 21 November 2018 / Published: 28 November 2018
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Abstract
Due to the so-called 3He shortage crisis, many detection techniques for thermal neutrons are currently based on alternative converters. There are several possible ways of increasing the detection efficiency for thermal neutrons using the solid neutron-to-charge converters 10B or 10B
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Due to the so-called 3He shortage crisis, many detection techniques for thermal neutrons are currently based on alternative converters. There are several possible ways of increasing the detection efficiency for thermal neutrons using the solid neutron-to-charge converters 10B or 10B4C. Here, we present an investigation of the Micromegas technology. The micro-pattern gaseous detector Micromegas was developed in the past years at Saclay and is now used in a wide variety of neutron experiments due to its combination of high accuracy, high rate capability, excellent timing properties, and robustness. A large high-efficiency Micromegas-based neutron detector is proposed for thermal neutron detection, containing several layers of 10B4C coatings that are mounted inside the gas volume. The principle and the fabrication of a single detector unit prototype with overall dimension of ~15 × 15 cm2 and its possibility to modify the number of 10B4C neutron converter layers are described. We also report results from measurements that are verified by simulations, demonstrating that typically five 10B4C layers of 1–2 μm thickness would lead to a detection efficiency of 20% for thermal neutrons and a spatial resolution of sub-mm. The high potential of this novel technique is given by the design being easily adapted to large sizes by constructing a mosaic of several such detector units, resulting in a large area coverage and high detection efficiencies. An alternative way of achieving this is to use a multi-layered Micromegas that is equipped with two-side 10B4C-coated gas electron multiplier (GEM)-type meshes, resulting in a robust and large surface detector. Another innovative and very promising concept for cost-effective, high-efficiency, large-scale neutron detectors is by stacking 10B4C-coated microbulk Micromegas. A prototype was designed and built, and the tests so far look very encouraging. Full article
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Open AccessConference Report Quantum Dynamics of Charged Fermions in the Wigner Formulation of Quantum Mechanics
Universe 2018, 4(12), 133; https://doi.org/10.3390/universe4120133
Received: 11 October 2018 / Revised: 9 November 2018 / Accepted: 20 November 2018 / Published: 23 November 2018
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Abstract
To study the kinetic properties of dense quantum plasma, a new quantum dynamics method in the Wigner representation of quantum mechanics has been developed for extreme conditions, when analytical approximations based on different kinds of perturbation theories cannot be applied. This method combines
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To study the kinetic properties of dense quantum plasma, a new quantum dynamics method in the Wigner representation of quantum mechanics has been developed for extreme conditions, when analytical approximations based on different kinds of perturbation theories cannot be applied. This method combines the Feynman and Wigner formulation of quantum mechanics and uses for calculation the path integral Monte-Carlo (WPIMC) in phase space and quantum generalization of the classical molecular dynamics methods (WMD) allowing to solve the quantum Wigner–Liouville-like equation. The Fermi–Dirac statistical effects are accounted for by the effective pair pseudopotential depending on coordinates and momenta and allowing to avoid the famous “sign problem” due to realization of the Pauli blocking of fermions. Significant influence of the interparticle interaction on the high energy asymptotics of the momentum distribution functions have been observed. According to the quantum Kubo formula, we also study the electron conductivity of dense plasma media. Full article
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Open AccessArticle SU(2) Quantum Yang–Mills Thermodynamics: Some Theory and Some Applications
Universe 2018, 4(12), 132; https://doi.org/10.3390/universe4120132
Received: 27 September 2018 / Revised: 13 November 2018 / Accepted: 15 November 2018 / Published: 22 November 2018
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Abstract
In the first part of this talk, we review some prerequisites for and essential arguments involved in the construction of the thermal-ground-state estimate underlying the deconfining phase in the thermodynamics of SU(2) Quantum Yang–Mills theory and how this structure supports its distinct excitations.
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In the first part of this talk, we review some prerequisites for and essential arguments involved in the construction of the thermal-ground-state estimate underlying the deconfining phase in the thermodynamics of SU(2) Quantum Yang–Mills theory and how this structure supports its distinct excitations. The second part applies deconfining SU(2) Yang–Mills thermodynamics to the Cosmic Microwave Background in view of (i) a modified temperature-redshift relation with an interesting link to correlation-length criticality in the 3D Ising model, (ii) the implied minimal changes in the dark sector of the cosmological model, and (iii) best-fit parameter values of this model when confronted with the spectra of the angular two-point functions temperature-temperature (TT), temperature-E-mode-polarisation (TE), E-mode-polarisation-E-mode-polarisation (EE), excluding the low-l physics. The latter, which so far is treated in an incomplete way due to the omission of radiative effects, is addressed in passing. Full article
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Universe EISSN 2218-1997 Published by MDPI AG, Basel, Switzerland RSS E-Mail Table of Contents Alert
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