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21 pages, 1051 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

New Exact Solutions of Relativistic Hydrodynamics for Longitudinally Expanding Fireballs

by Tamás Csörgő, Gábor Kasza, Máté Csanád and Zefang Jiang

Universe 2018, 4(6), 69; https://doi.org/10.3390/universe4060069 - 1 Jun 2018

Cited by 18 | Viewed by 3570

Abstract

We present new, exact, finite solutions of relativistic hydrodynamics for longitudinally expanding fireballs for arbitrary constant value of the speed of sound. These new solutions generalize earlier, longitudinally finite, exact solutions, from an unrealistic to a reasonable equation of state, characterized by a [...] Read more.

We present new, exact, finite solutions of relativistic hydrodynamics for longitudinally expanding fireballs for arbitrary constant value of the speed of sound. These new solutions generalize earlier, longitudinally finite, exact solutions, from an unrealistic to a reasonable equation of state, characterized by a temperature independent (average) value of the speed of sound. Observables such as the rapidity density and the pseudorapidity density are evaluated analytically, resulting in simple and easy to fit formulae that can be matched to the high energy proton–proton and heavy ion collision data at RHIC and LHC. In the longitudinally boost-invariant limit, these new solutions approach the Hwa–Bjorken solution and the corresponding rapidity distributions approach a rapidity plateaux. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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14 pages, 595 KiB

Open AccessArticle

Scaling Properties of Spectra in New Exact Solutions of Rotating, Multi-Component Fireball Hydrodynamics

by Tamás Csörgő and Gábor Kasza

Universe 2018, 4(4), 58; https://doi.org/10.3390/universe4040058 - 26 Mar 2018

Cited by 5 | Viewed by 2760

Abstract

We describe fireballs that rehadronize from a perfect fluid of quark matter, characterized by the lattice QCD equation of state, to a chemically frozen, multi-component mixture, that contains various kinds of observable hadrons. For simplicity and clarity, we apply a non-relativistic approximation to [...] Read more.

We describe fireballs that rehadronize from a perfect fluid of quark matter, characterized by the lattice QCD equation of state, to a chemically frozen, multi-component mixture, that contains various kinds of observable hadrons. For simplicity and clarity, we apply a non-relativistic approximation to describe the kinematics of this expansion. Unexpectedly, we identify a secondary explosion that may characterize fireball hydrodynamics at the QCD critical point. After rehadronization, the multi-component mixture of hadrons keeps on rotating and expanding together, similarly to a single component fluid. After kinetic freeze-out, the effective temperature

T_{i}

of the single-particle spectra of hadron type

h_{i}

is found to be a sum of the kinetic freeze-out temperature

T_{f}

(that is independent of the hadron type

h_{i}

) and a term proportional to the mass

m_{i}

of hadron type

h_{i}

. The coefficient of proportionality to

m_{i}

is found to be independent of the hadron type

h_{i}

but to be dependent on the radial flow and vorticity of collective dynamics. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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7 pages, 1197 KiB

Open AccessArticle

PHENIX Results of Three-Particle Bose-Einstein Correlations in \({\sqrt{s_{NN}}}\) = 200 GeV Au+Au Collisions

by Tamás Novák

Universe 2018, 4(3), 57; https://doi.org/10.3390/universe4030057 - 19 Mar 2018

Cited by 2 | Viewed by 2662

Abstract

Bose-Einstein correlations (BECs) of identical hadrons reveal information about hadron creation from the strongly interacting matter formed in ultrarelativistic heavy-ion collisions. The measurement of three-particle correlations may in particular shed light on hadron creation mechanisms beyond thermal/chaotic emission. In this paper, we show [...] Read more.

Bose-Einstein correlations (BECs) of identical hadrons reveal information about hadron creation from the strongly interacting matter formed in ultrarelativistic heavy-ion collisions. The measurement of three-particle correlations may in particular shed light on hadron creation mechanisms beyond thermal/chaotic emission. In this paper, we show the status of PHENIX measurements of three-pion correlations as a function of momentum differences within the triplets. We analyze the shape of the correlation functions through the assumption of Lévy sources and a proper treatment of the Coulomb interaction within the triplets. We measure the three-particle correlation strength (

λ_{3}

), which, together with the two-particle correlation strength

λ_{2}

, encodes information about hadron creation mechanisms. From a consistent analysis of two- and three-particle correlation strengths, we establish a new experimental measure of thermalization and coherence in the source. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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11 pages, 12899 KiB

Open AccessEditor’s ChoiceArticle

Investigating the Poor Match among Different Precessing Gravitational Waveforms

by Márton Tápai, Viktória Pintér, Tamás Tarjányi, Zoltán Keresztes and László Árpád Gergely

Universe 2018, 4(3), 56; https://doi.org/10.3390/universe4030056 - 16 Mar 2018

Viewed by 2893

Abstract

The sixfold direct detection of gravitational waves opened the era of gravitational wave astronomy. All of these gravitational waves were emitted by black hole or neutron star binaries. The determination of the parameters characterizing compact binaries requires the accurate knowledge of waveforms. Three [...] Read more.

The sixfold direct detection of gravitational waves opened the era of gravitational wave astronomy. All of these gravitational waves were emitted by black hole or neutron star binaries. The determination of the parameters characterizing compact binaries requires the accurate knowledge of waveforms. Three different waveforms (Spin Dominated, SpinTaylorT4 and Spinning Effective One Body fitted to Numerical Relativity, SEOBNR) are considered in the spin-aligned and precessing cases, in the parameter ranges where the larger spin dominates over the orbital angular momentum. The degeneracy in the parameter space of each waveform is analyzed, then the matches among the waveforms are investigated. Our results show that in the spin-aligned case only the inspiral Spin-dominated and SpinTaylorT4 waveforms agree well with each other. The highest matches of these with SEOBNR are at different parameters as compared to where SEOBNR shows the best match with itself, reflecting SEOBNR being full inspiral-merger-ringdown waveform, with coefficients fitted to numerical relativity, rather than arising from post-Newtonian (PN) calculations. In the precessing case, the matches between the pairs of all waveforms are significantly lower. We identify possible causes of this in (1) the implementation of the angular dynamics carried out at different levels of accuracy for different waveforms; (2) differences in the inclusiveness of the merger process and in the PN coefficients of the inspiral waveforms (Spin-Dominated, SpinTaylorT4) and the full SEOBNR waveform. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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12 pages, 940 KiB

Open AccessArticle

On Maximal Homogeneous 3-Geometries—A Polyhedron Algorithm for Space Tilings

by István Prok

Universe 2018, 4(3), 49; https://doi.org/10.3390/universe4030049 - 6 Mar 2018

Cited by 2 | Viewed by 3297

Abstract

In this paper we introduce a polyhedron algorithm that has been developed for finding space groups. In order to demonstrate the problem and the main steps of the algorithm, we consider some regular plane tilings in our examples, and then we generalize the [...] Read more.

In this paper we introduce a polyhedron algorithm that has been developed for finding space groups. In order to demonstrate the problem and the main steps of the algorithm, we consider some regular plane tilings in our examples, and then we generalize the method for 3-dimensional spaces. Applying the algorithm and its computer implementation we investigate periodic, face-to-face, regular polyhedron tilings in 3-spaces of constant curvature and of the other homogeneous 3-geometries, too. We summarize and visualize the most important results, emphasizing the fixed-point-free space groups which determine 3-dimensional manifolds. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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11 pages, 282 KiB

Open AccessFeature PaperArticle

Light-Like Shockwaves in Scalar-Tensor Theories

by Bence Racskó and László Árpád Gergely

Universe 2018, 4(3), 44; https://doi.org/10.3390/universe4030044 - 27 Feb 2018

Cited by 3 | Viewed by 2710

Abstract

Both electromagnetic shock-waves and gravitational waves propagate with the speed of light. If they carry significant energy-momentum, this will change the properties of the space-time they propagate through. This can be described in terms of the junction conditions between space-time regions separated by [...] Read more.

Both electromagnetic shock-waves and gravitational waves propagate with the speed of light. If they carry significant energy-momentum, this will change the properties of the space-time they propagate through. This can be described in terms of the junction conditions between space-time regions separated by a singular, null hypersurface. We derived generic junction conditions for Brans-Dicke theory in the Jordan frame, exploring a formalism based on a transverse vector, rather than normal, which can be applied to any type of hypersurfaces. In the particular case of a non-null hypersurface we obtain a generalised Lanczos equation, in which the jump of the extrinsic curvature is sourced by both the distributional energy-momentum tensor and by the jump in the transverse derivative of the scalar. In the case of null hypersurfaces, the distributional source is decomposed into surface density, current and pressure. The latter, however, ought to vanish by virtue of the scalar junction condition. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

9 pages, 1316 KiB

Open AccessArticle

Precessing Black Hole Binaries and Their Gravitational Radiation

by László Á. Gergely, Zoltán Keresztes and Márton Tápai

Universe 2018, 4(2), 40; https://doi.org/10.3390/universe4020040 - 16 Feb 2018

Cited by 1 | Viewed by 3542

Abstract

The first and second observational runs of Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) have marked the first direct detections of gravitational waves, either from black hole binaries or, in one case, from coalescing neutron stars. These observations opened up the era of gravitational [...] Read more.

The first and second observational runs of Advanced Laser Interferometer Gravitational-wave Observatory (LIGO) have marked the first direct detections of gravitational waves, either from black hole binaries or, in one case, from coalescing neutron stars. These observations opened up the era of gravitational wave astronomy, but also of gravitational wave cosmology, in the form of an independent derivation of the Hubble constant. They were equally important to prove false a plethora of modified gravity theories predicting gravitational wave propagation speed different from that of light. For a continued and improved testing of general relativity, the precise description of compact binary dynamics, not only in the final coalescence phase but also earlier, when precessional effects dominate, are required. We report on the derivation of the full secular dynamics for compact binaries, valid over the precessional time-scale, in the form of an autonomous closed system of differential equations for the set of spin angles and periastron. The system can be applied for mapping the parameter space for the occurrence of the spin flip-flop effect and for more accurately analyzing the spin-flip effect, which could explain the formation of X-shaped radio galaxies. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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11 pages, 369 KiB

Open AccessArticle

Geometric Aspects and Some Uses of Deformed Models of Thermostatistics

by Alexandre Gavrilik

Universe 2018, 4(2), 33; https://doi.org/10.3390/universe4020033 - 11 Feb 2018

Cited by 5 | Viewed by 2924

Abstract

We consider diverse deformed Bose gas models (DBGMs) focusing on distributions and correlations of any order, and also on deformed thermodynamics. For so-called

μ

-deformed Bose gas model (

μ

-DBGM), main thermodynamic aspects are treated: total number of particles, deformed partition function, [...] Read more.

We consider diverse deformed Bose gas models (DBGMs) focusing on distributions and correlations of any order, and also on deformed thermodynamics. For so-called

μ

-deformed Bose gas model (

μ

-DBGM), main thermodynamic aspects are treated: total number of particles, deformed partition function, etc. Using a geometric approach, we confirm the existence of critical behavior—Bose-like condensation; we find the critical temperature

T_{c}^{(μ)}

depending on

μ

so that

T_{c}^{(μ)} > T_{c}^{(Bose)}

for

μ > 0

. This fact and other advantages of

μ

-DBGM relative to the usual Bose gas, e.g., stronger effective inter-particle attraction (controlled by the parameter

μ

), allow us to consider the condensate in

μ

-DBGM as a candidate for modeling dark matter. As another, quite successful application we discuss the usage of the two-parameter (

\tilde{μ}, q

)-deformed BGM for effective description of the peculiar (non-Bose like) behavior of two-pion correlations observed in the STAR experiment at RHIC (Brookhaven). Herein, we point out the transparent role of the two deformation parameters

\tilde{μ}

and q as being responsible for compositeness and (effective account of) interactions of pions, respectively. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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8 pages, 4623 KiB

Open AccessArticle

Centrality Dependent Lévy-Stable Two-Pion Bose-Einstein Correlations in \( {\sqrt{s_{NN}}} \) = 200 GeV Au+Au Collisions at the PHENIX Experiment

by Sándor Lökös

Universe 2018, 4(2), 31; https://doi.org/10.3390/universe4020031 - 9 Feb 2018

Cited by 12 | Viewed by 3205

Abstract

Investigation of femtoscopic correlation functions in relativistic heavy ion reactions is an important tool to access the space-time structure of particle production in the strongly interacting Quark Gluon Plasma (sQGP). The shape of the source, and thus the shape of the correlation functions, [...] Read more.

Investigation of femtoscopic correlation functions in relativistic heavy ion reactions is an important tool to access the space-time structure of particle production in the strongly interacting Quark Gluon Plasma (sQGP). The shape of the source, and thus the shape of the correlation functions, is often assumed to be Gaussian, but experimental results found evidence for heavy tails in the source distribution of pions. Recent analysis revealed that the statistically correct assumption could be the so-called Lévy distribution. The detailed investigation of correlation functions in various systems may shed light on the location of the critical endpoint on QCD (Quantum Chromodynamics) phase diagram. It could also reveal if there is partially coherent pion production or could indicate the possible in-medium mass modification of the

η^{'}

meson due to the (partial) restoration of the

U_{A} (1)

axial symmetry. These phenomena could depend on the system size and on the collision energy. A detailed centrality-dependent analysis could explore the multiplicity dependencies of the Lévy parameters, and thus the critical and thermodynamical properties of the sQGP, and could give information about the above mentioned processes. In this paper, we present the status of the centrality dependent measurements of two-pion Lévy Bose-Einstein correlation functions

\sqrt{s_{NN}} = 200

GeV Au+Au collisions at PHENIX.
Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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10 pages, 2653 KiB

Open AccessArticle

Exclusive Particle Production in pp and pPb Collisions at CMS

by Oliver Suranyi

Universe 2018, 4(2), 25; https://doi.org/10.3390/universe4020025 - 5 Feb 2018

Viewed by 3143

Abstract

Exclusive processes provide a useful method to study a broad range of high energy physics fields from gluon density evolutions to searches for new physics. Three measurements from the Compact Muon Solenoid experiment are reviewed. Exclusive

π π

production is studied in proton–proton [...] Read more.

Exclusive processes provide a useful method to study a broad range of high energy physics fields from gluon density evolutions to searches for new physics. Three measurements from the Compact Muon Solenoid experiment are reviewed. Exclusive

π π

production is studied in proton–proton collisions. Low-mass meson resonances are observed in the invariant mass distribution of pion pairs. The total exclusive

π^{+} π^{-}

cross-section is also measured in the

p_{T} (π) > 0.2

GeV,

| y | < 2

region, yielding

26.5 \pm 0.3 (stat) \pm 5.0 (syst) \pm 1.1 (lumi) μ

b. The photoproduction of

Y (n S)

mesons is observed in ultraperipheral pPb collisions. The differential cross-sections are measured as a function of

| t |

and y. The comparison with previous measurements and theoretical models provides a better understanding of the gluon density evolution at low x values. Evidence for the

γ γ \to W^{+} W^{-}

process is shown with a

3.7 σ

observed significance. According to the results, limits on anomalous quartic gauge couplings can be provided. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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10 pages, 332 KiB

Open AccessArticle

On the High-Energy Neutrino Emission from Active Galactic Nuclei

by Emma Kun, Peter L. Biermann, Silke Britzen and László Á. Gergely

Universe 2018, 4(2), 24; https://doi.org/10.3390/universe4020024 - 1 Feb 2018

Cited by 4 | Viewed by 3388

Abstract

We review observational aspects of the active galactic nuclei and their jets in connection with the detection of high-energy neutrinos by the Antarctic IceCube Neutrino Observatory. We propose that a reoriented jet generated by the spin-flipping supermassive black hole in a binary merger [...] Read more.

We review observational aspects of the active galactic nuclei and their jets in connection with the detection of high-energy neutrinos by the Antarctic IceCube Neutrino Observatory. We propose that a reoriented jet generated by the spin-flipping supermassive black hole in a binary merger is likely the source of such high-energy neutrinos. Hence they encode important information on the afterlife of coalescing supermassive black hole binaries. As the gravitational radiation emanating from them will be monitored by the future LISA space mission, high-energy neutrino detections could be considered a contributor to multi-messenger astronomy. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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12 pages, 257 KiB

Open AccessArticle

Non-Euclidean Geometry, Nontrivial Topology and Quantum Vacuum Effects

by Yurii A. Sitenko and Volodymyr M. Gorkavenko

Universe 2018, 4(2), 23; https://doi.org/10.3390/universe4020023 - 31 Jan 2018

Cited by 3 | Viewed by 2922

Abstract

Space out of a topological defect of the Abrikosov–Nielsen–Olesen (ANO) vortex type is locally flat but non-Euclidean. If a spinor field is quantized in such a space, then a variety of quantum effects are induced in the vacuum. On the basis of the [...] Read more.

Space out of a topological defect of the Abrikosov–Nielsen–Olesen (ANO) vortex type is locally flat but non-Euclidean. If a spinor field is quantized in such a space, then a variety of quantum effects are induced in the vacuum. On the basis of the continuum model for long-wavelength electronic excitations originating in the tight-binding approximation for the nearest-neighbor interaction of atoms in the crystal lattice, we consider quantum ground-state effects in Dirac materials with two-dimensional monolayer structures warped into nanocones by a disclination; the nonzero size of the disclination is taken into account, and a boundary condition at the edge of the disclination is chosen to ensure self-adjointness of the Dirac–Weyl Hamiltonian operator. We show that the quantum ground-state effects are independent of the disclination size, and we find circumstances in which they are independent of parameters of the boundary condition. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

9 pages, 1022 KiB

Open AccessFeature PaperArticle

Scaling Properties of the Mean Multiplicity and Pseudorapidity Density in e⁻+e⁺, e^±+p, p( p ¯ )+p, p+A and A+A(B) Collisions

by Roy A. Lacey, Peifeng Liu, Niseem Magdy, Máté Csanád, Benjamin Schweid, Nuggehalli N. Ajitanand, John Alexander and Robert Pak

Universe 2018, 4(1), 22; https://doi.org/10.3390/universe4010022 - 22 Jan 2018

Cited by 18 | Viewed by 2814

Abstract

The charged-particle pseudorapidity density (

d N_{ch} / d η

) for p(

\bar{p}

)+p, p+A and A+A(B) collisions and the mean multiplicity

⟨ N_{ch} ⟩

for e

^{-}

+e

^{+}

,

e^{\pm} + p

, and p( [...] Read more.

The charged-particle pseudorapidity density (

d N_{ch} / d η

) for p(

\bar{p}

)+p, p+A and A+A(B) collisions and the mean multiplicity

〈 N_{ch} 〉

for e

^{-}

+e

^{+}

,

e^{\pm} + p

, and p(

\bar{p}

)+p collisions are studied for a wide range of beam energies (

\sqrt{s}

). Characteristic scaling patterns are observed for both

d N_{ch} / d η

and

〈 N_{ch} 〉

, consistent with a thermal particle production mechanism for the bulk of the soft particles created in all of these systems. The scaling patterns found also validate an essential role for quark participants in these collisions. The measured values for

d N_{ch} / d η

and

〈 N_{ch} 〉

are observed to factorize into contributions that depend on

log (\sqrt{s})

and the number of nucleon or quark participant pairs

N_{pp}

. The quantification of these contributions gives expressions that serve to systematize

d N_{ch} / d η

and

〈 N_{ch} 〉

measurements spanning nearly 4 orders of magnitude in

\sqrt{s}

and to predict their values as a function of

\sqrt{s}

and

N_{pp}

. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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11 pages, 321 KiB

Open AccessArticle

Pure-Connection Gravity and Anisotropic Singularities

by Kirill Krasnov and Yuri Shtanov

Universe 2018, 4(1), 12; https://doi.org/10.3390/universe4010012 - 4 Jan 2018

Cited by 2 | Viewed by 2775

Abstract

In four space-time dimensions, there exists a special infinite-parameter family of chiral modified gravity theories. They are most properly described by a connection field, with space-time metric being a secondary and derived concept. All these theories have the same number of degrees of [...] Read more.

In four space-time dimensions, there exists a special infinite-parameter family of chiral modified gravity theories. They are most properly described by a connection field, with space-time metric being a secondary and derived concept. All these theories have the same number of degrees of freedom as general relativity, which is the only parity-invariant member of this family. Modifications of general relativity can be arranged so as to become important in regions with large curvature. In this paper, we review how a certain simple modification of this sort can resolve the Schwarzschild black-hole and Kasner anisotropic singularities of general relativity. In the corresponding solutions, the fundamental connection field is regular in space-time. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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6 pages, 1088 KiB

Open AccessArticle

Lévy Analysis of HBT Correlation Functions in s N N = 62 GeV and 39 GeV Au + Au Collisions at PHENIX

by Dániel Kincses

Universe 2018, 4(1), 11; https://doi.org/10.3390/universe4010011 - 4 Jan 2018

Cited by 10 | Viewed by 2981

Abstract

The phase diagram of strongly interacting matter can be explored by analyzing data of heavy-ion collisions at different center of mass collision energies. For investigating the space-time structure of the hadron emission source, Bose-Einstein or HBT correlation measurements are among the best tools. [...] Read more.

The phase diagram of strongly interacting matter can be explored by analyzing data of heavy-ion collisions at different center of mass collision energies. For investigating the space-time structure of the hadron emission source, Bose-Einstein or HBT correlation measurements are among the best tools. In this paper we present the latest results from the PHENIX experiment of the Relativistic Heavy Ion Collider (RHIC) on such measurements in

\sqrt{s_{N N}} =

39 GeV and 62 GeV Au + Au collisions. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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8 pages, 254 KiB

Open AccessArticle

Entropic Distance for Nonlinear Master Equation

by Tamás Sándor Biró, András Telcs and Zoltán Néda

Universe 2018, 4(1), 10; https://doi.org/10.3390/universe4010010 - 4 Jan 2018

Cited by 4 | Viewed by 2853

Abstract

More and more works deal with statistical systems far from equilibrium, dominated by unidirectional stochastic processes, augmented by rare resets. We analyze the construction of the entropic distance measure appropriate for such dynamics. We demonstrate that a power-like nonlinearity in the state probability [...] Read more.

More and more works deal with statistical systems far from equilibrium, dominated by unidirectional stochastic processes, augmented by rare resets. We analyze the construction of the entropic distance measure appropriate for such dynamics. We demonstrate that a power-like nonlinearity in the state probability in the master equation naturally leads to the Tsallis (Havrda–Charvát, Aczél–Daróczy) q-entropy formula in the context of seeking for the maximal entropy state at stationarity. A few possible applications of a certain simple and linear master equation to phenomena studied in statistical physics are listed at the end. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

7 pages, 228 KiB

Open AccessArticle

Hamiltonian Dynamics of Doubly-Foliable Space-Times

by Cecília Gergely, Zoltán Keresztes and László Árpád Gergely

Universe 2018, 4(1), 9; https://doi.org/10.3390/universe4010009 - 3 Jan 2018

Cited by 2 | Viewed by 2798

Abstract

The 2 + 1 + 1 decomposition of space-time is useful in monitoring the temporal evolution of gravitational perturbations/waves in space-times with a spatial direction singled-out by symmetries. Such an approach based on a perpendicular double foliation has been employed in the framework [...] Read more.

The 2 + 1 + 1 decomposition of space-time is useful in monitoring the temporal evolution of gravitational perturbations/waves in space-times with a spatial direction singled-out by symmetries. Such an approach based on a perpendicular double foliation has been employed in the framework of dark matter and dark energy-motivated scalar-tensor gravitational theories for the discussion of the odd sector perturbations of spherically-symmetric gravity. For the even sector, however, the perpendicularity has to be suppressed in order to allow for suitable gauge freedom, recovering the 10th metric variable. The 2 + 1 + 1 decomposition of the Einstein–Hilbert action leads to the identification of the canonical pairs, the Hamiltonian and momentum constraints. Hamiltonian dynamics is then derived via Poisson brackets. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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4 pages, 193 KiB

Open AccessArticle

Parallels of Belated Recognition: Bolyai János and Károlyházy Frigyes

by György Kádár

Universe 2018, 4(1), 8; https://doi.org/10.3390/universe4010008 - 3 Jan 2018

Viewed by 3032

Abstract

There was an obvious parallelism between the lives of the two Hungarian men of science: János Bolyai a genial geometer and Frigyes Károlyházy a missionary of education in the field of modern physics. Both of them selected and solved a complex problem that [...] Read more.

There was an obvious parallelism between the lives of the two Hungarian men of science: János Bolyai a genial geometer and Frigyes Károlyházy a missionary of education in the field of modern physics. Both of them selected and solved a complex problem that was too difficult for the majority of scientists of their times. Their work was criticized authoritatively by high rank scientists of their discipline, which led to their withdrawal from science. The belated recognition of the Non-Euclidean geometry and the gravity inspired quantum-mechanical state reduction put these excellent achievements to their deserved right place. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

10 pages, 326 KiB

Open AccessArticle

Universal Hyperbolic Geometry, Sydpoints and Finite Fields: A Projective and Algebraic Alternative

by Norman J. Wildberger

Universe 2018, 4(1), 3; https://doi.org/10.3390/universe4010003 - 1 Jan 2018

Cited by 3 | Viewed by 5350

Abstract

Universal hyperbolic geometry gives a purely algebraic approach to the subject that connects naturally with Einstein’s special theory of relativity. In this paper, we give an overview of some aspects of this theory relating to triangle geometry and in particular the remarkable new [...] Read more.

Universal hyperbolic geometry gives a purely algebraic approach to the subject that connects naturally with Einstein’s special theory of relativity. In this paper, we give an overview of some aspects of this theory relating to triangle geometry and in particular the remarkable new analogues of midpoints called sydpoints. We also discuss how the generality allows us to consider hyperbolic geometry over general fields, in particular over finite fields. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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7 pages, 912 KiB

Open AccessArticle

Lévy Femtoscopy with PHENIX at RHIC

by Máté Csanád

Universe 2017, 3(4), 85; https://doi.org/10.3390/universe3040085 - 18 Dec 2017

Cited by 7 | Viewed by 3121

Abstract

In this paper we present the measurement of charged pion two-particle femtoscopic correlation functions in

\sqrt{s_{N N}} = 200

GeV Au + Au collisions in 31 average transverse mass bins, separately for positive and negative pion pairs. Lévy-shaped source distributions yield a [...] Read more.

In this paper we present the measurement of charged pion two-particle femtoscopic correlation functions in

\sqrt{s_{N N}} = 200

GeV Au + Au collisions in 31 average transverse mass bins, separately for positive and negative pion pairs. Lévy-shaped source distributions yield a statistically acceptable description of the measured correlation functions, with three physical parameters: correlation strength parameter

λ

, Lévy index

α

and Lévy scale parameter R. The transverse mass dependence of these Lévy parameters is then investigated. Their physical interpretation is also discussed, and the appearance of a new scaling variable is observed. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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9 pages, 1481 KiB

Open AccessArticle

Perturbative Accelerating Solutions of Relativistic Hydrodynamics

by Bálint Kurgyis and Máté Csanád

Universe 2017, 3(4), 84; https://doi.org/10.3390/universe3040084 - 14 Dec 2017

Cited by 4 | Viewed by 3114

Abstract

In ultra-relativistic collisions of heavy ions, the strongly interacting Quark Gluon Plasma (sQGP) is created. The fluid nature of the sQGP was one of the important discoveries of high energy heavy ion physics in the last decades. Henceforth the explosion of this matter [...] Read more.

In ultra-relativistic collisions of heavy ions, the strongly interacting Quark Gluon Plasma (sQGP) is created. The fluid nature of the sQGP was one of the important discoveries of high energy heavy ion physics in the last decades. Henceforth the explosion of this matter may be described by hydrodynamical models. Besides numerical simulations, it is important to study the analytic solutions of the equations of hydrodynamics, as these enable us to understand the connection of the final and initial states better. In this paper we present a perturbative, accelerating solution of relativistic hydrodynamics, on top of a known class of solutions describing Hubble-expansion. We describe the properties of this class of perturbative solutions, and investigate a few selected solutions in detail. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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12 pages, 2223 KiB

Open AccessArticle

On Maximal Homogeneous 3-Geometries and Their Visualization

by Emil Molnár, István Prok and Jeno Szirmai

Universe 2017, 3(4), 83; https://doi.org/10.3390/universe3040083 - 4 Dec 2017

Cited by 3 | Viewed by 3759

Abstract

The motivation for this talk and paper is related to the classification of the homogeneous simply connected maximal 3-geometries (the so-called Thurston geometries:

E^{3}

,

S^{3}

,

H^{3}

,

S^{2} \times R

,

H^{2} \times R

, [...] Read more.

The motivation for this talk and paper is related to the classification of the homogeneous simply connected maximal 3-geometries (the so-called Thurston geometries:

E^{3}

,

S^{3}

,

H^{3}

,

S^{2} \times R

,

H^{2} \times R

,

\tilde{S L_{2} R}

,

Nil

, and

Sol

) and their applications in crystallography. The first author found in (Molnár 1997) (see also the more popular (Molnár et al. 2010; 2015) with co-author colleagues, together with more details) a unified projective interpretation for them in the sense of Felix Klein’s Erlangen Program: namely, each S of the above space geometries and its isometry group

Isom (S)

can be considered as a subspace of the projective 3-sphere:

S \subset P S^{3}

, where a special maximal group

G = Isom (S) \subseteq Coll (P S^{3})

of collineations acts, leaving the above subspace S invariant. Vice-versa, we can start with the projective geometry, namely with the classification of

Coll (P S^{3})

through linear transforms of dual pairs of real 4-vector spaces

(V^{4}, V_{4}, R, \sim)

=

P S^{3}

(up to positive real multiplicative equivalence ∼) via Jordan normal forms. Then, we look for projective groups with 3 parameters, and with appropriate properties for convenient geometries described above and in this paper. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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5 pages, 330 KiB

Open AccessArticle

Enhancement of Elliptic Flow of π⁻ under Intense Magnetic Field in √ ^sNN = 200 GeV Au+Au Collisions: A (2 + 1)-Dimensional Reduced-MHD Model Study

by Victor Roy

Universe 2017, 3(4), 82; https://doi.org/10.3390/universe3040082 - 30 Nov 2017

Cited by 2 | Viewed by 2504

Abstract

We investigate the effect of intense magnetic fields on the

(2 + 1)

-dimensional reduced- magnetohydrodynamical (MHD) expansion of hot and dense quark–gluon plasma (QGP) produced in

\sqrt{s_{NN}}

= 200 GeV Au+Au collisions. For the sake of simplicity, we consider [...] Read more.

We investigate the effect of intense magnetic fields on the

(2 + 1)

-dimensional reduced- magnetohydrodynamical (MHD) expansion of hot and dense quark–gluon plasma (QGP) produced in

\sqrt{s_{NN}}

= 200 GeV Au+Au collisions. For the sake of simplicity, we consider the case in which the magnetic field points in the direction perpendicular to the reaction plane. We also consider this field to be external, with energy density parametrized as a two-dimensional Gaussian. The width of the Gaussian along the directions orthogonal to the beam axis varies with the centrality of the collision. The dependence of the magnetic field on proper time (

τ

) is parametrized for the case of zero and finite electrical conductivity of the QGP. We solve the equations of motion of ideal hydrodynamics for such an external magnetic field. For collisions with a non-zero impact parameter we observe a considerable increase in the elliptic-flow coefficient

v_{2}

of

π^{-}

in the presence of an external magnetic field, and the increment in

v_{2}

is found to depend on the evolution and the initial magnitude of the magnetic field. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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8 pages, 1176 KiB

Open AccessArticle

Effective Interactions and Prospects for Resolution of the Fundamental Cosmological Problems in Quantum Gravity

by Boris A. Arbuzov

Universe 2017, 3(4), 80; https://doi.org/10.3390/universe3040080 - 15 Nov 2017

Viewed by 3915

Abstract

Wouldbe consequences of the existence of effective interactions in quantum gravitation theory are considered. In the framework of the approach, the example of a running gravitational coupling is presented, corresponding to an adequate description of effects, which nowadays are usually prescribed to dark [...] Read more.

Wouldbe consequences of the existence of effective interactions in quantum gravitation theory are considered. In the framework of the approach, the example of a running gravitational coupling is presented, corresponding to an adequate description of effects, which nowadays are usually prescribed to dark matter and dark energy. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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10 pages, 2115 KiB

Open AccessFeature PaperArticle

Femtoscopy with Identified Hadrons in pp, pPb, and PbPb Collisions in CMS

by Ferenc Siklér

Universe 2017, 3(4), 76; https://doi.org/10.3390/universe3040076 - 8 Nov 2017

Cited by 3 | Viewed by 3260

Abstract

Short-range correlations of identified charged hadrons in pp (

\sqrt{s} =

0.9, 2.76, and 7 TeV), pPb (

\sqrt{s_{_{NN}}} =

5.02 TeV), and peripheral PbPb collisions (

\sqrt{s_{_{NN}}} =

2.76 TeV) are studied with the CMS detector at the LHC. Charged [...] Read more.

Short-range correlations of identified charged hadrons in pp (

\sqrt{s} =

0.9, 2.76, and 7 TeV), pPb (

\sqrt{s_{_{NN}}} =

5.02 TeV), and peripheral PbPb collisions (

\sqrt{s_{_{NN}}} =

2.76 TeV) are studied with the CMS detector at the LHC. Charged pions, kaons, and protons at low momentum and in laboratory pseudorapidity

| η | < 1

are identified via their energy loss in the silicon tracker. The two-particle correlation functions show effects of quantum statistics, Coulomb interaction, and also indicate the role of multi-body resonance decays and mini-jets. The characteristics of the one-, two-, and three-dimensional correlation functions are studied as a function of transverse pair momentum,

k_{T}

, and the charged-particle multiplicity of the event. The extracted radii are in the range 1–5 fm, reaching highest values for very high multiplicity pPb, also for similar multiplicity PbPb collisions, and decrease with increasing

k_{T}

. The dependence of radii on multiplicity and

k_{T}

largely factorizes and appears to be insensitive to the type of the colliding system and center-of-mass energy. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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Other

Jump to: Research

5 pages, 209 KiB

Open AccessConference Report

Geometry of Bigravity

by Vladimir Soloviev

Universe 2018, 4(2), 19; https://doi.org/10.3390/universe4020019 - 31 Jan 2018

Cited by 1 | Viewed by 2461

Abstract

The non-Euclidean geometry created by Bolyai, Lobachevsky and Gauss has led to a new physical theory—general relativity. In due turn, a correct mathematical treatment of the cosmological problem in general relativity has led Friedmann to a discovery of dynamical equations for the universe. [...] Read more.

The non-Euclidean geometry created by Bolyai, Lobachevsky and Gauss has led to a new physical theory—general relativity. In due turn, a correct mathematical treatment of the cosmological problem in general relativity has led Friedmann to a discovery of dynamical equations for the universe. And now, after almost a century of theoretical and experimental research, cosmology has a status of the most rapidly developing fundamental science. New challenges here are problems of dark energy and dark matter. As a result, a lot of modifications of general relativity appear recently. The bigravity is one of them, constructed with a couple of interacting space–time metrics accompanied by some coupling to matter. We discuss here this approach and different kinds of the coupling. Full article

(This article belongs to the Special Issue BGL2017: 10th Bolyai-Gauss-Lobachevsky Conference on Non-Euclidean Geometry and Its Applications)

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