Universe

41 pages, 669 KiB

Open AccessReview

Gamma-ray Emission and Variability Processes in High-Energy-Peaked BL Lacertae Objects

by Bidzina Kapanadze

Universe 2023, 9(7), 344; https://doi.org/10.3390/universe9070344 - 24 Jul 2023

Viewed by 1483

BL Lac objects are active galactic nuclei notable for a beamed nonthermal radiation, which is generated in one of the relativistic jets forming a small angle to the observer’s line-of-sight. The broadband spectra of BL Lacs show a two-component spectral energy distribution (SED). [...] Read more.

BL Lac objects are active galactic nuclei notable for a beamed nonthermal radiation, which is generated in one of the relativistic jets forming a small angle to the observer’s line-of-sight. The broadband spectra of BL Lacs show a two-component spectral energy distribution (SED). High-energy-peaked BL Lacs (HBLs) exhibit their lower-energy (synchrotron) peaks at UV to X-ray frequencies. The origin of the higher-energy SED component, representing the

γ

-ray range in HBLs, is still controversial and different emission scenarios (one- and multi-zone synchrotron self-Compton, hadronic etc.) are proposed. In

γ

-rays, HBLs show a complex flaring behavior with rapid and large-amplitude TeV-band variations on timescales down to a few minutes. This review presents a detailed characterization of the hypothetical emission mechanisms which could contribute to the

γ

-ray emission, their application to the nearby TeV-detected HBLs, successes in the broadband SED modeling and difficulties in the interpretation of the observational data. I also overview the unstable processes to be responsible for the observed

γ

-ray variability and particle energization up to millions of Lorentz factors (relativistic shocks, magnetic reconnection, turbulence and jet-star interaction). Finally, the future prospects for solving the persisting problems by means of the dedicated gamma-ray observations and sophisticated simulations are also addressed. Full article

(This article belongs to the Special Issue Recent Advances in Gamma Ray Astrophysics and Future Perspectives)

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18 pages, 409 KiB

Open AccessArticle

Newtonian Cosmology and Evolution of κ-Deformed Universe

by E. Harikumar, Harsha Sreekumar and Suman Kumar Panja

Universe 2023, 9(7), 343; https://doi.org/10.3390/universe9070343 - 24 Jul 2023

Cited by 3 | Viewed by 967

Abstract

Considering space-time to be non-commutative, we study the evolution of the universe employing the approach of Newtonian cosmology. Generalizing the conservation of energy and the first law of thermodynamics to

κ

-deformed space-time, we derive the modified Friedmann equations, valid up to the [...] Read more.

Considering space-time to be non-commutative, we study the evolution of the universe employing the approach of Newtonian cosmology. Generalizing the conservation of energy and the first law of thermodynamics to

κ

-deformed space-time, we derive the modified Friedmann equations, valid up to the first order, in the deformation parameter. Analyzing these deformed equations, we derive the time evolution of the scale factor in cases of radiation-dominated, matter-dominated, and vacuum (energy)-dominated universes. We show that the rate of change of the scale factor in all three situations is modified by the non-commutativity of space-time, and this rate depends on the sign of the deformation parameter, indicating a possible explanation for the observed Hubble tension. We undertake this investigation for two different realizations of non-commutative space-time coordinates. In both cases, we also argue for the existence of bounce in the evolution of the universe. Full article

(This article belongs to the Special Issue Quantum Field Theory in Curved Spacetime and Its Implications for Cosmology, Blackholes and Quantum Gravity)

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13 pages, 426 KiB

Open AccessArticle

Excitation Functions of Related Temperatures of η and η⁰ Emission Sources from Squared Momentum Transfer Spectra in High-Energy Collisions

by Qi Wang, Fu-Hu Liu and Khusniddin K. Olimov

Universe 2023, 9(7), 342; https://doi.org/10.3390/universe9070342 - 23 Jul 2023

Viewed by 925

Abstract

The squared momentum transfer spectra of

η

and

η^{0}

, produced in high-energy photon–proton (

γ p

)

\to η (η^{0}) + p

processes in electron–proton (

e p

) collisions performed at CEBAF, NINA, CEA, SLAC, DESY, and [...] Read more.

The squared momentum transfer spectra of

η

and

η^{0}

, produced in high-energy photon–proton (

γ p

)

\to η (η^{0}) + p

processes in electron–proton (

e p

) collisions performed at CEBAF, NINA, CEA, SLAC, DESY, and WLS are analyzed. The Monte Carlo calculations are used in the analysis of the squared momentum transfer spectra, where the transfer undergoes from the incident

γ

to emitted

η (η^{0})

or equivalently from the target proton to emitted proton. In the calculations, the Erlang distribution and Tsallis–Levy function are used to describe the transverse momentum (

p_{T}

) spectra of emitted particles. Our results show that the average transverse momentum (

⟨ p_{T} ⟩

), the initial-state temperature (

T_{i}

), and the final-state temperature (

T_{0}

) roughly decrease from the lower center-of-mass energy (W) to the higher one in the concerned energy range of a few GeV, which is different from the excitation function from heavy-ion collisions in the similar energy range. Full article

(This article belongs to the Special Issue Collectivity in High-Energy Proton-Proton and Heavy-Ion Collisions)

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16 pages, 594 KiB

Open AccessArticle

Differential Geometry of the Family of Helical Hypersurfaces with a Light-like Axis in Minkowski Spacetime

L^{4}

by Erhan Güler

Universe 2023, 9(7), 341; https://doi.org/10.3390/universe9070341 - 21 Jul 2023

Cited by 1 | Viewed by 989

Abstract

We investigate the class of helical hypersurfaces parametrized by

x = x (u, v, w)

, characterized by a light-like axis in Minkowski spacetime

L^{4}

. We determine the matrices that represent the fundamental forms, Gauss map, and [...] Read more.

We investigate the class of helical hypersurfaces parametrized by

x = x (u, v, w)

, characterized by a light-like axis in Minkowski spacetime

L^{4}

. We determine the matrices that represent the fundamental forms, Gauss map, and shape operator of

x

. Furthermore, employing the Cayley–Hamilton theorem, we compute the curvatures associated with

x

. We explore the conditions under which the curvatures of

x

possess the property of being umbilical. Moreover, we provide the Laplace–Beltrami operator for the family of helical hypersurfaces with a light-like axis in

L^{4}

. Full article

(This article belongs to the Section Mathematical Physics)

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32 pages, 1878 KiB

Open AccessReview

Modeling and Testing Screening Mechanisms in the Laboratory and in Space

by Valeri Vardanyan and Deaglan J. Bartlett

Universe 2023, 9(7), 340; https://doi.org/10.3390/universe9070340 - 20 Jul 2023

Cited by 5 | Viewed by 839

Abstract

The non-linear dynamics of scalar fields coupled to matter and gravity can lead to remarkable density-dependent screening effects. In this short review, we present the main classes of screening mechanisms, and discuss their tests in laboratory and astrophysical systems. We particularly focused on [...] Read more.

The non-linear dynamics of scalar fields coupled to matter and gravity can lead to remarkable density-dependent screening effects. In this short review, we present the main classes of screening mechanisms, and discuss their tests in laboratory and astrophysical systems. We particularly focused on reviewing numerical and technical aspects involved in modeling the non-linear dynamics of screening and on tests using laboratory experiments and astrophysical systems, such as stars, galaxies, and dark matter halos. Full article

(This article belongs to the Special Issue Cosmological Constant)

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16 pages, 592 KiB

Open AccessArticle

Stability Analysis of a Self-Gravitating Fluid within EIT Theory

by J. Félix Salazar, A. L. García-Perciante, A. R. Méndez and G. Chacón-Acosta

Universe 2023, 9(7), 339; https://doi.org/10.3390/universe9070339 - 19 Jul 2023

Viewed by 839

Abstract

In this article, we apply the formalism of (classical) Extended Irreversible Thermodynamics (EIT) to the dynamics of density fluctuations for a self-gravitating fluid in a static Universe, considering only bulk viscosity. The problem is characterized by gravitational instability, for which the Jeans criterion [...] Read more.

In this article, we apply the formalism of (classical) Extended Irreversible Thermodynamics (EIT) to the dynamics of density fluctuations for a self-gravitating fluid in a static Universe, considering only bulk viscosity. The problem is characterized by gravitational instability, for which the Jeans criterion is shown to hold. However, both the relaxation time in the constitutive equation and the viscosity itself affect the behavior of both stable and unstable modes. In particular, the stable scenario features three modes, two of them corresponding to damped oscillations which decay faster that in the CIT scene. The third mode, inexistent in the CIT, corresponds to a very quickly decaying mode. In the unstable case, growing modes are observed in both EIT and CIT theories, for which the slowest growth is the one predicted by the CIT theory followed by the EIT, while the non-dissipative case corresponds to the fastest one. Full article

(This article belongs to the Section Cosmology)

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10 pages, 478 KiB

Open AccessArticle

Excited States of Maximal Warm Holes

by Yuan Yue and Yong-Qiang Wang

Universe 2023, 9(7), 338; https://doi.org/10.3390/universe9070338 - 19 Jul 2023

Cited by 1 | Viewed by 848

Abstract

Recently, the Einstein–Maxwell–scalar model with a non-minimal coupling between the scalar and Maxwell fields was explored. As a result, a new class of black hole solutions with scalar hair was discovered. By fixing the mass of a black hole and taking the maximum [...] Read more.

Recently, the Einstein–Maxwell–scalar model with a non-minimal coupling between the scalar and Maxwell fields was explored. As a result, a new class of black hole solutions with scalar hair was discovered. By fixing the mass of a black hole and taking the maximum allowable charge, an extremal black hole was obtained. Interestingly, this extremal black hole not only possesses an event horizon with a non-zero surface area but also exhibits a non-zero Hawking temperature. This unique type of extremal black hole is referred to as a maximal warm hole (MWH). In this paper, we revisit this model and examine these black holes with highly excited state fields. We discovered that an excited state MWH solution can also be obtained under extremal conditions. We investigate the range of existence for excited states and analyze their relevant physical properties. Full article

(This article belongs to the Section Gravitation)

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86 pages, 692 KiB

Open AccessReview

Quantum Mechanics and Quantum Field Theory: Algebraic and Geometric Approaches

by Igor Frolov and Albert Schwarz

Universe 2023, 9(7), 337; https://doi.org/10.3390/universe9070337 - 17 Jul 2023

Cited by 3 | Viewed by 1465

Abstract

This is a non-standard exposition of the main notions of quantum mechanics and quantum field theory, including recent results. It is based on the algebraic approach in which the starting point is a star-algebra and on the geometric approach in which the starting [...] Read more.

This is a non-standard exposition of the main notions of quantum mechanics and quantum field theory, including recent results. It is based on the algebraic approach in which the starting point is a star-algebra and on the geometric approach in which the starting point is a convex set of states. Standard formulas for quantum probabilities are derived from decoherence. This derivation allows us to go beyond quantum theory in the geometric approach. Particles are defined as elementary excitations of the ground state (and quasiparticles as elementary excitations of any translation invariant state). The conventional scattering matrix does not work for quasiparticles (or even for particles if the theory does not have particle interpretation). The analysis of scattering in these cases is based on the notion of an inclusive scattering matrix, which is closely related to inclusive cross-sections. It is proven that the conventional scattering matrix can be expressed in terms of Green functions (LSZ formula) and the inclusive scattering matrix can be expressed in terms of generalized Green functions that appear in the Keldysh formalism of non-equilibrium statistical physics. The derivation of the expression of the evolution operator and other physical quantities in terms of functional integrals is based on the notion of the symbol of an operator; these arguments can be applied in the geometric approach as well. In particular, this result can be used to provide a simple derivation of the diagram technique for generalized Green functions. The notion of an inclusive scattering matrix makes sense in the geometric approach, although it seems that a definition of the conventional scattering matrix cannot be provided in this situation. The geometric approach is used to show that quantum mechanics and its generalizations can be considered as classical theories where our devices are able to measure only a part of the observables. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2023—Field Theory)

12 pages, 1524 KiB

Open AccessCommunication

Charged Kaon Femtoscopy with Lévy Sources in

\sqrt{s_{NN}}

= 200 GeV Au+Au Collisions at PHENIX

by László Kovács

Universe 2023, 9(7), 336; https://doi.org/10.3390/universe9070336 - 17 Jul 2023

Cited by 2 | Viewed by 948

Abstract

The PHENIX experiment measured two-particle Bose–Einstein quantum-statistical correlations of charged kaons in Au+Au collisions at

\sqrt{s_{NN}}

= 200 GeV. The correlation functions are parametrized assuming that the source emitting the particles has a Lévy shape, characterized by the Lévy exponent

α

and [...] Read more.

The PHENIX experiment measured two-particle Bose–Einstein quantum-statistical correlations of charged kaons in Au+Au collisions at

\sqrt{s_{NN}}

= 200 GeV. The correlation functions are parametrized assuming that the source emitting the particles has a Lévy shape, characterized by the Lévy exponent

α

and the Lévy scale R. By introducing the intercept parameter

λ

, we account for the core–halo fraction. The parameters are investigated as a function of transverse mass. The comparison of the parameters measured for kaon–kaon with those measured from pion–pion correlation may clarify the connection of Lévy parameters to physical processes. Full article

(This article belongs to the Special Issue Zimányi School – Heavy Ion Physics)

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12 pages, 6565 KiB

Open AccessCommunication

Charged Particle Pseudorapidity Distributions Measured with the STAR EPD

by Mátyás Molnár

Universe 2023, 9(7), 335; https://doi.org/10.3390/universe9070335 - 15 Jul 2023

Viewed by 1177

Abstract

In 2018, in preparation for the Beam Energy Scan II, the STAR detector was upgraded with the Event Plane Detector (EPD). The instrument enhanced STAR’s capabilities in centrality determination for fluctuation measurements, event plane resolution for flow measurements, and in triggering overall. Due [...] Read more.

In 2018, in preparation for the Beam Energy Scan II, the STAR detector was upgraded with the Event Plane Detector (EPD). The instrument enhanced STAR’s capabilities in centrality determination for fluctuation measurements, event plane resolution for flow measurements, and in triggering overall. Due to its fine radial granularity, it can also be utilized to measure pseudorapidity distributions of the produced charged primary particles, in EPD’s pseudorapidity coverage of

2.15 < | η | < 5.09

. As such a measurement cannot be done directly, the response of the detector to the primary particles has to be understood well. The detector response matrix was determined via Monte Carlo simulations, and corrected charged particle pseudorapidity distributions were obtained in Au + Au collisions at the center of mass collision energies

\sqrt{s_{_{N N}}}

= 19.6 and 27.0 GeV using an iterative unfolding procedure. Several systematic checks of the method were also done. Full article

(This article belongs to the Special Issue Zimányi School – Heavy Ion Physics)

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0 pages, 970 KiB

Open AccessArticle

Estimates of the Surface Magnetic Field Strength of Radio Pulsars

by Vitaliy Kim, Adel Umirbayeva and Yerlan Aimuratov

Universe 2023, 9(7), 334; https://doi.org/10.3390/universe9070334 - 14 Jul 2023

Cited by 2 | Viewed by 1296 | Correction

Abstract

We investigate the geometry of the magnetic field of rotation-powered pulsars. A new method for calculating an angle (

β

) between the spin and magnetic dipole axes of a neutron star (NS) in the ejector stage is considered within the frame of [...] Read more.

We investigate the geometry of the magnetic field of rotation-powered pulsars. A new method for calculating an angle (

β

) between the spin and magnetic dipole axes of a neutron star (NS) in the ejector stage is considered within the frame of the magnetic dipole energy loss mechanism. We estimate the surface magnetic field strength (

B_{ns}

) for a population of known neutron stars in the radio pulsar (ejector) stage. The evaluated

B_{ns} (β)

may differ by an order of magnitude from the values without considering the angle

β

. It is shown that

B_{ns} (β)

lies in the range

10^{8}

–

10^{14} G

for a known population of short and middle periodic radio pulsars. Full article

(This article belongs to the Special Issue Remo Ruffini Festschrift)

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13 pages, 284 KiB

Open AccessArticle

De Sitter-Invariant Black Holes

by Diego F. López, Salman Abarghouei Nejad and José G. Pereira

Universe 2023, 9(7), 333; https://doi.org/10.3390/universe9070333 - 14 Jul 2023

Cited by 1 | Viewed by 1495

Abstract

In the de Sitter-invariant approach to gravitation, all solutions to the gravitational field equations are spacetimes that reduce locally to de Sitter. Consequently, besides including a Schwarzschild event horizon, the de Sitter-invariant black hole also has a de Sitter cosmic horizon. Accordingly, it [...] Read more.

In the de Sitter-invariant approach to gravitation, all solutions to the gravitational field equations are spacetimes that reduce locally to de Sitter. Consequently, besides including a Schwarzschild event horizon, the de Sitter-invariant black hole also has a de Sitter cosmic horizon. Accordingly, it can lodge matter and dark energies. Owing to this additional structure concerning Poincaré-invariant general relativity, such a black hole can establish a link between the black hole dynamics and the universe’s evolution. Possible implications for cosmology are discussed, and a comparison with recent observations indicating the existence of a cosmological coupling of black holes is presented. Full article

(This article belongs to the Section Gravitation)

12 pages, 855 KiB

Open AccessArticle

Neutron Star Binaries Produced by Binary-Driven Hypernovae, Their Mergers, and the Link between Long and Short GRBs

by Laura M. Becerra, Chris Fryer, Jose F. Rodriguez, Jorge A. Rueda and Remo. Ruffini

Universe 2023, 9(7), 332; https://doi.org/10.3390/universe9070332 - 12 Jul 2023

Viewed by 942

Abstract

The binary-driven hypernova (BdHN) model explains long gamma-ray bursts (GRBs) associated with supernovae (SNe) Ic through physical episodes that occur in a binary composed of a carbon-oxygen (CO) star and a neutron star (NS) companion in close orbit. The CO core collapse triggers [...] Read more.

The binary-driven hypernova (BdHN) model explains long gamma-ray bursts (GRBs) associated with supernovae (SNe) Ic through physical episodes that occur in a binary composed of a carbon-oxygen (CO) star and a neutron star (NS) companion in close orbit. The CO core collapse triggers the cataclysmic event, originating the SN and a newborn NS (hereafter

ν

NS) at its center. The

ν

NS and the NS accrete SN matter. BdHNe are classified based on the NS companion fate and the GRB energetics, mainly determined by the orbital period. In BdHNe I, the orbital period is of a few minutes, so the accretion causes the NS to collapse into a Kerr black hole (BH), explaining GRBs of energies >

10^{52}

erg. BdHN II, with longer periods of tens of minutes, yields a more massive but stable NS, accounting for GRBs of

10^{50}

–

10^{52}

erg. BdHNe III have still longer orbital periods (e.g., hours), so the NS companion has a negligible role, which explains GRBs with a lower energy release of <

10^{50}

erg. BdHN I and II might remain bound after the SN, so they could form NS-BH and binary NS (BNS), respectively. In BdHN III, the SN likely disrupts the system. We perform numerical simulations of BdHN II to compute the characteristic parameters of the BNS left by them, their mergers, and the associated short GRBs. We obtain the mass of the central remnant, whether it is likely to be a massive NS or a BH, the conditions for disk formation and its mass, and the event’s energy release. The role of the NS nuclear equation of state is outlined. Full article

(This article belongs to the Special Issue Remo Ruffini Festschrift)

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15 pages, 4607 KiB

Open AccessArticle

Characterizing Low-Energy Charged Particles in the Magnetosphere with the LEM CubeSat Spectrometer Project: Detector Concept and Hardware Characterisation

by Riccardo Nicolaidis, Francesco Nozzoli, Giancarlo Pepponi, Pierluigi Bellutti, Evgeny Demenev, Francesco Maria Follega, Roberto Iuppa and Veronica Vilona

Universe 2023, 9(7), 331; https://doi.org/10.3390/universe9070331 - 11 Jul 2023

Viewed by 942

Abstract

An accurate flux measurement of low-energy charged particles trapped in the magnetosphere is necessary for space weather characterization and to study the coupling between the lithosphere and magnetosphere, which allows for the investigation of the correlations between seismic events and particle precipitation from [...] Read more.

An accurate flux measurement of low-energy charged particles trapped in the magnetosphere is necessary for space weather characterization and to study the coupling between the lithosphere and magnetosphere, which allows for the investigation of the correlations between seismic events and particle precipitation from Van Allen belts. In this work, the project of a CubeSat space spectrometer, the low-energy module (LEM), is shown. The detector will be able to perform an event-based measurement of the energy, arrival direction, and composition of low-energy charged particles down to 0.1 MeV. Moreover, thanks to a CdZnTe mini-calorimeter, the LEM spectrometer also allows for photon detection in the sub-MeV range, joining the quest for the investigation of the nature of gamma-ray bursts (GRBs) and terrestrial gamma-ray flashes (TGFs). The particle identification of the LEM relies on the

Δ E - E

technique performed by thin silicon detectors. This multipurpose spectrometer will fit within a 10 × 10 × 10

{cm}^{3}

CubeSat frame, and it will be constructed as a joint project between the University of Trento, FBK, and INFN-TIFPA. To fulfil the size and mass requirements, an innovative approach, based on active particle collimation, was designed for the LEM; this avoids the heavy/bulky passive collimators of previous space detectors. In this paper, we will present the LEM geometry, its detection concept, the results from the developed GEANT4 simulation, and some characterisations of a candidate silicon detector for the instrument payload. Full article

(This article belongs to the Special Issue Selected Papers from the 2nd International Electronic Conference on Universe (ECU 2023))

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12 pages, 6849 KiB

Open AccessCommunication

Blinkverse: A Database of Fast Radio Bursts

by Jiaying Xu, Yi Feng, Di Li, Pei Wang, Yongkun Zhang, Jintao Xie, Huaxi Chen, Han Wang, Zhixuan Kang, Jingjing Hu, Yun Zheng, Chao-Wei Tsai, Xianglei Chen and Dengke Zhou

Universe 2023, 9(7), 330; https://doi.org/10.3390/universe9070330 - 11 Jul 2023

Cited by 15 | Viewed by 1585

Abstract

The volume of research on fast radio bursts (FRBs) observation have been seeing a dramatic growth. To facilitate the systematic analysis of the FRB population, we established a database platform, Blinkverse, as a central inventory of FRBs from various observatories and with published [...] Read more.

The volume of research on fast radio bursts (FRBs) observation have been seeing a dramatic growth. To facilitate the systematic analysis of the FRB population, we established a database platform, Blinkverse, as a central inventory of FRBs from various observatories and with published properties, particularly dynamic spectra from FAST, CHIME, GBT, Arecibo, etc. Blinkverse thus not only forms a superset of FRBCAT, TNS, and CHIME/FRB, but also provides convenient access to thousands of FRB dynamic spectra from FAST, some of which were not available before. Blinkverse is regularly maintained and will be updated by external users in the future. Data entries of FRBs can be retrieved through parameter searches through FRB location, fluence, etc., and their logical combinations. Interactive visualization was built into the platform. We analyzed the energy distribution, period analysis, and classification of FRBs based on data downloaded from Blinkverse. The energy distributions of repeaters and non-repeaters are found to be distinct from one another. Full article

(This article belongs to the Special Issue Research on Origins and Natures of Fast Radio Bursts)

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17 pages, 1907 KiB

Open AccessArticle

Dark Matter in Fractional Gravity II: Tests in Galaxy Clusters

by Francesco Benetti, Andrea Lapi, Giovanni Gandolfi, Balakrishna Sandeep Haridasu and Luigi Danese

Universe 2023, 9(7), 329; https://doi.org/10.3390/universe9070329 - 10 Jul 2023

Cited by 4 | Viewed by 1354

Abstract

Recently, in Benetti et al. (Astrophys. J. 2023, 949, 65), we suggested that the dark matter (DM) component in galaxies may originate fractional gravity. In such a framework, the DM component exists, but the gravitational potential associated to its density distribution is determined [...] Read more.

Recently, in Benetti et al. (Astrophys. J. 2023, 949, 65), we suggested that the dark matter (DM) component in galaxies may originate fractional gravity. In such a framework, the DM component exists, but the gravitational potential associated to its density distribution is determined by a modified Poisson equation including fractional derivatives (i.e., derivatives of noninteger type), which are meant to describe nonlocal effects; as such, this scenario is different from theories where baryonic matter emulates DM-like effects via modifications of gravity (e.g., MONDian frameworks). In Benetti et al., we showed that fractional gravity worked very well for reproducing the kinematics of disk-dominated galaxies, especially dwarfs; there is also preliminary evidence that the strength of fractional effects tends to weaken toward more massive systems. Here, we aim to test fractional gravity in galaxy clusters, with a twofold aim: (i) perform an independent sanity check that it can accurately describe such large and massive structures; (ii) derive a clear-cut trend for its strength in systems with different DM masses. To this purpose, we forward model the density and pressure distributions of the intracluster medium (ICM), working out the hydrostatic equilibrium equation in fractional gravity. Then, we perform a Bayesian analysis of the X-COP galaxy cluster sample and infer constraints on the fractional gravity parameters, for individual clusters as well as stacked clusters. We find that fractional gravity performs remarkably well in modeling the ICM profiles for the X-COP sample. We also check that the DM concentration vs. mass relation is still consistent with the expectations of N-body simulations in the standard cosmological scenario. Finally, we confirm the weakening of the fractional gravity effects toward more massive systems and derive the overall scaling of the fractional gravity parameters from dwarf galaxies to massive clusters, spanning six orders of magnitude in DM mass. Such an overall trend implies that fractional gravity can substantially alleviate the small-scale issues of the standard DM paradigm, while remaining successful on large cosmological scales. Full article

(This article belongs to the Section Galaxies and Clusters)

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11 pages, 533 KiB

Open AccessArticle

Coulomb Corrections for Bose–Einstein Correlations from One- and Three-Dimensional Lévy-Type Source Functions

by Bálint Kurgyis, Dániel Kincses, Márton Nagy and Máté Csanád

Universe 2023, 9(7), 328; https://doi.org/10.3390/universe9070328 - 10 Jul 2023

Cited by 15 | Viewed by 1074

Abstract

In the study of femtoscopic correlations in high-energy physics, besides Bose–Einstein correlations, one has to take final-state interactions into account. Amongst them, Coulomb interactions play a prominent role in the case of charged particles. Recent measurements have shown that in heavy-ion collisions, Bose–Einstein [...] Read more.

In the study of femtoscopic correlations in high-energy physics, besides Bose–Einstein correlations, one has to take final-state interactions into account. Amongst them, Coulomb interactions play a prominent role in the case of charged particles. Recent measurements have shown that in heavy-ion collisions, Bose–Einstein correlations can be best described by Lévy-type sources instead of the more common Gaussian assumption. Furthermore, three-dimensional measurements have indicated that, depending on the choice of frame, a deviation from spherical symmetry observed under the assumption of Gaussian source functions persists in the case of Lévy-type sources. To clarify such three-dimensional Lévy-type correlation measurements, it is thus important to study the effect of Coulomb interactions in the case of non-spherical Lévy sources. We calculated the Coulomb correction factor numerically in the case of such a source function for assorted kinematic domains and parameter values using the Metropolis–Hastings algorithm and compared our results with previous methods to treat Coulomb interactions in the presence of Lévy sources. Full article

(This article belongs to the Special Issue Zimányi School – Heavy Ion Physics)

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6 pages, 244 KiB

Open AccessCommunication

A Simple, Exact Formulation of Number Counts in the Geodesic-Light-Cone Gauge

by Giuseppe Fanizza, Maurizio Gasperini and Giovanni Marozzi

Universe 2023, 9(7), 327; https://doi.org/10.3390/universe9070327 - 10 Jul 2023

Viewed by 832

Abstract

In this article, we compare different formulations of the number count prescription using the convenient formalism of the Geodesic-Light-Cone gauge. We then find a simple, exact, and very general expression of such a prescription which is suitable for generalised applications. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2023—Cosmology)

14 pages, 813 KiB

Open AccessArticle

Silicon Photomultipliers for Neutrino Telescopes

by Diego Real and David Calvo

Universe 2023, 9(7), 326; https://doi.org/10.3390/universe9070326 - 10 Jul 2023

Viewed by 1104

Abstract

Neutrino astronomy has opened a new window to the extreme Universe, entering into a fruitful era built upon the success of neutrino telescopes, which have already given a new step forward in this novel and growing field by the first observation of steady [...] Read more.

Neutrino astronomy has opened a new window to the extreme Universe, entering into a fruitful era built upon the success of neutrino telescopes, which have already given a new step forward in this novel and growing field by the first observation of steady point-like sources already achieved by IceCube. Neutrino telescopes equipped with Silicon PhotoMultipliers (SiPMs) will significantly increase in number, because of their excellent time resolution and the angular resolution, and will be in better condition to detect more steady sources as well as the unexpected. The use of SiPMs represents a challenge to the acquisition electronics because of the fast signals as well as the high levels of dark noise produced by SiPMs. The acquisition electronics need to include a noise rejection scheme by implementing a coincidence filter between channels. This work discusses the advantages and disadvantages of using SiPMs for the next generation of neutrino telescopes, focusing on the possible developments that could help for their adoption in the near future. Full article

(This article belongs to the Special Issue Recent Advances in Double Beta Decay Investigations: In Honor of Prof. Sabin Stoica at His 70th Anniversary)

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10 pages, 418 KiB

Open AccessArticle

ϕ(2170) Decaying to ϕππ and ϕ

K \bar{K}

by Yun-Hua Chen

Universe 2023, 9(7), 325; https://doi.org/10.3390/universe9070325 - 9 Jul 2023

Cited by 1 | Viewed by 825

Abstract

Within the framework of dispersion theory, we study the the processes

e^{+} e^{-} \to ϕ (2170) \to ϕ π π (K \bar{K})

. The strong pion–pion final-state interactions, especially the

K \bar{K}

coupled channel in [...] Read more.

Within the framework of dispersion theory, we study the the processes

e^{+} e^{-} \to ϕ (2170) \to ϕ π π (K \bar{K})

. The strong pion–pion final-state interactions, especially the

K \bar{K}

coupled channel in the S wave, are taken into account in a model-independent way using the Omnès function solution. Through fitting the experimental data of the

π π

and

ϕ π

invariant mass distributions of the

e^{+} e^{-} \to ϕ (2170) \to ϕ π^{+} π^{-}

process, the low-energy constants in the chiral Lagrangian are determined. The theoretical prediction for the cross sections’ ratio

σ (e^{+} e^{-} \to ϕ (2170) \to ϕ K^{+} K^{-}) / σ (e^{+} e^{-} \to ϕ (2170) \to

ϕ π^{+} π^{-})

is given, which could be useful for selecting the physical solution, when the fit to the

e^{+} e^{-} \to ϕ K^{+} K^{-}

cross-section distribution is available in the future. Our results suggest that above the kinematical threshold of

ϕ K \bar{K}

, the mechanism

e^{+} e^{-} \to ϕ K^{+} K^{-}

, with the kaons rescattering to a pion pair, plays an important role in the

e^{+} e^{-} \to ϕ π^{+} π^{-}

transition. Full article

(This article belongs to the Special Issue Recent Progress in Hadron Spectroscopy)

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45 pages, 2330 KiB

Open AccessReview

Vector Quarkonia at the LHC with Jethad: A High-Energy Viewpoint

by Francesco Giovanni Celiberto

Universe 2023, 9(7), 324; https://doi.org/10.3390/universe9070324 - 7 Jul 2023

Cited by 12 | Viewed by 1097

Abstract

In this review, we discuss and extend the study of the inclusive production of vector quarkonia,

J / ψ

and

Υ

, emitted with large transverse momenta and rapidities at the LHC. We adopt the novel ZCW19

^{+}

determination of fragmentation functions to [...] Read more.

In this review, we discuss and extend the study of the inclusive production of vector quarkonia,

J / ψ

and

Υ

, emitted with large transverse momenta and rapidities at the LHC. We adopt the novel ZCW19

^{+}

determination of fragmentation functions to depict the quarkonium production mechanism at the next-to-leading level of perturbative QCD. This approach is based on the nonrelativistic QCD formalism well adapted to describe the formation of a quarkonium state from the collinear fragmentation of a gluon or a constituent heavy quark at the lowest energy scale. We rely upon the

NLL / {NLO}^{+}

hybrid high-energy and collinear factorization for differential cross-sections, where the collinear formalism is enhanced by the BFKL resummation of next-to-leading energy logarithms arising in the t-channel. We employ the method to analyze the behavior of the rapidity distributions for double-inclusive vector quarkonium and inclusive vector quarkonium plus jet emissions. We discover that the natural stability of the high-energy series, previously seen in observables sensitive to the emission of hadrons with heavy flavor detected in the rapidity acceptance of LHC barrel calorimeters, becomes even more manifest when these particles are tagged in forward regions covered by endcaps. Our findings present the important message that vector quarkonia at the LHC via hybrid factorization offer a unique chance to perform precision studies of high-energy QCD, as well as an intriguing opportunity to shed light on the quarkonium production puzzle. Full article

(This article belongs to the Special Issue Recent Progress in Hadron Spectroscopy)

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10 pages, 598 KiB

Open AccessCommunication

Improved Model of Primordial Black Hole Formation after Starobinsky Inflation

by Sultan Saburov and Sergei V. Ketov

Universe 2023, 9(7), 323; https://doi.org/10.3390/universe9070323 - 6 Jul 2023

Cited by 12 | Viewed by 914

Abstract

A new (improved) model of inflation and primordial black hole (PBH) formation is proposed by combining the Starobinsky model of inflation, Appleby–Battye–Starobinsky (ABS) model of dark energy, and a quantum correction in the modified

F (R)

gravity. The energy scale parameter [...] Read more.

A new (improved) model of inflation and primordial black hole (PBH) formation is proposed by combining the Starobinsky model of inflation, Appleby–Battye–Starobinsky (ABS) model of dark energy, and a quantum correction in the modified

F (R)

gravity. The energy scale parameter in the ABS model is taken to be close to the inflationary scale, in order to describe double inflation instead of dark energy. The quantum correction is given by the term quartic in the spacetime scalar curvature R with a negative coefficient

(- δ)

in the

F (R)

function. It is demonstrated that very good agreement (within

1 σ

) with current measurements of the cosmic microwave background (CMB) radiation can be achieved by choosing the proper value of

δ

, thus solving the problem of low values of the tilt of CMB scalar perturbations in the earlier proposed model in arXiv:2205.00603. A large (by a factor of

10^{7}

against CMB) enhancement in the power spectrum of scalar perturbations is achieved by fine tuning the parameters of the model. It is found by numerical analysis that it can lead to formation of asteroid-size PBHs with masses up to

10^{20}

g, which may form dark matter in the current universe. Full article

(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)

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14 pages, 840 KiB

Open AccessArticle

Measurements of J/ψ Production vs. Event Multiplicity in Forward Rapidity in p + p Collisions in the PHENIX Experiment

by Zhaozhong Shi

Universe 2023, 9(7), 322; https://doi.org/10.3390/universe9070322 - 4 Jul 2023

Cited by 2 | Viewed by 990

Abstract

J / ψ

, a charmonium bound state made of a charm and an anti-charm quark, was discovered in the 1970s and confirmed the quark model. Because the mass of charm quarks is significantly above the quantum chromodynamics (QCD) scale [...] Read more.

J / ψ

, a charmonium bound state made of a charm and an anti-charm quark, was discovered in the 1970s and confirmed the quark model. Because the mass of charm quarks is significantly above the quantum chromodynamics (QCD) scale

Λ_{Q C D}

, charmonia are considered excellent probes to test perturbative quantum chromodynamics (pQCD) calculations. In recent decades, they have been studied extensively at different high-energy colliders. However, their production mechanisms, which involve multiple scales, are still not very well understood. Recently, in high-multiplicity

p + p

collisions at RHIC and at the LHC, a significant enhancement of

J / ψ

production yield has been observed, which suggests a strong contribution of multi-parton interaction (MPI). This is different from the traditional pQCD picture, where charm quark pairs are produced from a single hard scattering between partons in

p + p

collisions. In this work, we will report the

J / ψ

normalized production yield as a function of normalized charged particle multiplicity over a board range of rapidity and event multiplicity in the

J / ψ \to μ^{+} μ^{-}

channel with PHENIX Run 15

p + p

data at

\sqrt{s} = 200

GeV. The results are compared with PYTHIA 8 simulations with the MPI option turned on and off. Finally, the outlooks of

J / ψ

in

p + A u

and

A u + p

collisions, along with color glass condensate (CGC) predictions and the multiplicity-dependent

ψ (2 S) / J / ψ

ratio in

p + p

data, will be briefly discussed. Full article

(This article belongs to the Special Issue Zimányi School – Heavy Ion Physics)

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10 pages, 359 KiB

Open AccessArticle

First Experimental Survey of a Whole Class of Non-Commutative Quantum Gravity Models in the VIP-2 Lead Underground Experiment

by Kristian Piscicchia, Antonino Marcianò, Andrea Addazi, Diana Laura Sirghi, Massimiliano Bazzi, Nicola Bortolotti, Mario Bragadireanu, Michael Cargnelli, Alberto Clozza, Luca De Paolis, Raffaele Del Grande, Carlo Guaraldo, Mihail Iliescu, Matthias Laubenstein, Simone Manti, Johann Marton, Marco Miliucci, Fabrizio Napolitano, Federico Nola, Alessio Porcelli, Alessandro Scordo, Francesco Sgaramella, Florin Sirghi, Oton Vazquez Doce, Johann Zmeskal and Catalina Curceanu Show full author list Hide full author list

Universe 2023, 9(7), 321; https://doi.org/10.3390/universe9070321 - 4 Jul 2023

Cited by 1 | Viewed by 1135

Abstract

This study is aimed to set severe constraints on a whole class of non-commutative space-times scenarios as a class of universality for several quantum gravity models. To this end, slight violations of the Pauli exclusion principle—predicted by these models—are investigated by searching for [...] Read more.

This study is aimed to set severe constraints on a whole class of non-commutative space-times scenarios as a class of universality for several quantum gravity models. To this end, slight violations of the Pauli exclusion principle—predicted by these models—are investigated by searching for Pauli forbidden K

_{α}

and K

_{β}

transitions in lead. The selection of a high atomic number target material allows to test the energy scale of the space-time non-commutativity emergence at high atomic transition energies. As a consequence, the measurement is very sensitive to high orders in the power series expansion of the Pauli violation probability, which allows to set the first constraint to the “triply special relativity” model proposed by Kowalski-Glikman and Smolin. The characteristic energy scale of the model is bound to

Λ > 5.6 \cdot 10^{- 9}

Planck scales. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2023—Gravitation)

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15 pages, 717 KiB

Open AccessArticle

Quasinormal Modes of a Charged Black Hole with Scalar Hair

by Wen-Di Guo and Qin Tan

Universe 2023, 9(7), 320; https://doi.org/10.3390/universe9070320 - 3 Jul 2023

Cited by 2 | Viewed by 948

Abstract

Based on the five-dimensional Einstein–Maxwell theory, Bah et al. constructed a singularity-free topology star/black hole [Phys. Rev. Lett. 126, 151101 (2021)]. After performing the Kaluza–Klein reduction, i.e., integrating the extra space dimension, it can obtain an effective four-dimensional spherically static charged black hole [...] Read more.

Based on the five-dimensional Einstein–Maxwell theory, Bah et al. constructed a singularity-free topology star/black hole [Phys. Rev. Lett. 126, 151101 (2021)]. After performing the Kaluza–Klein reduction, i.e., integrating the extra space dimension, it can obtain an effective four-dimensional spherically static charged black hole with scalar hair. In this paper, we study the quasinormal modes (QNMs) of the scalar, electromagnetic, and gravitational fields in the background of this effective four-dimensional charged black hole. The radial parts of the perturbed fields all satisfy a Schrödinger-like equation. Using the asymptotic iteration method, we obtain the QNM frequencies semianalytically. For low-overtone QNMs, the results obtained using both the asymptotic iteration method and the Wentzel–Kramers–Brillouin approximation method agree well. In the null coordinates, the evolution of a Gaussian package is also studied. The QNM frequencies obtained by fitting the evolution data also agree well with the results obtained using the asymptotic iteration method. Full article

(This article belongs to the Section Gravitation)

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32 pages, 15307 KiB

Open AccessReview

Cosmic-Ray Acceleration and Magnetic Fields in Galaxy Clusters and Beyond: Insights from Radio Observations

by Denis Wittor

Universe 2023, 9(7), 319; https://doi.org/10.3390/universe9070319 - 3 Jul 2023

Cited by 2 | Viewed by 1297

Abstract

The discovery of diffuse radio emission in galaxy clusters proved the existence of energetic cosmic-ray electrons and cosmic magnetic fields on Mpc-scales in the Universe. Furthermore, both magnetic fields and cosmic-ray electrons are predicted to exist beyond galaxy clusters, namely, in the filaments [...] Read more.

The discovery of diffuse radio emission in galaxy clusters proved the existence of energetic cosmic-ray electrons and cosmic magnetic fields on Mpc-scales in the Universe. Furthermore, both magnetic fields and cosmic-ray electrons are predicted to exist beyond galaxy clusters, namely, in the filaments and voids of the cosmic web. Recent detection of diffuse radio emission in intercluster bridges—the region between two merging clusters—strengthens the theory that both cosmic magnetic fields and cosmic-ray electrons exist on these large scales. Radio observations are our most powerful tool to study cosmic magnetic fields and cosmic-ray electrons in the Universe. The recent improvements in radio astronomy, including the exploration of the low-frequency radio sky, have led to the discovery of countless new radio sources, and hence a new understanding of the origin and evolution of cosmic magnetic fields and cosmic-ray electrons. In this contribution, we summarise the newest discoveries in the field. Furthermore, we discuss what these new radio observations teach us about cosmic magnetic fields and cosmic rays in galaxy clusters and beyond. Full article

(This article belongs to the Special Issue Diffuse Gas in Galaxy Clusters: Thermal and Non-thermal Properties)

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14 pages, 673 KiB

Open AccessArticle

Centrality-Dependent Lévy HBT Analysis in

\sqrt{s_{_{NN}}} = 5.02

TeV PbPb Collisions at CMS

by Balázs Kórodi

Universe 2023, 9(7), 318; https://doi.org/10.3390/universe9070318 - 1 Jul 2023

Cited by 1 | Viewed by 1002

Abstract

The measurement of two-particle Bose–Einstein momentum correlation functions are presented using

\sqrt{s_{_{NN}}} = 5.02

TeV PbPb collision data, recorded by the CMS experiment in 2018. The measured correlation functions are discussed in terms of Lévy-type source distributions. The Lévy source parameters are [...] Read more.

The measurement of two-particle Bose–Einstein momentum correlation functions are presented using

\sqrt{s_{_{NN}}} = 5.02

TeV PbPb collision data, recorded by the CMS experiment in 2018. The measured correlation functions are discussed in terms of Lévy-type source distributions. The Lévy source parameters are extracted as functions of transverse mass and collision centrality. These source parameters include the correlation strength

λ

, the Lévy stability index

α

, and the Lévy scale parameter R. The source shape, characterized by

α

, is found to be neither Gaussian nor Cauchy. A hydrodynamic-like scaling of R is also observed. Full article

(This article belongs to the Special Issue Zimányi School – Heavy Ion Physics)

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39 pages, 2281 KiB

Open AccessArticle

Effects of a Late Gravitational Transition on Gravitational Waves and Anticipated Constraints

by Evangelos Achilleas Paraskevas and Leandros Perivolaropoulos

Universe 2023, 9(7), 317; https://doi.org/10.3390/universe9070317 - 30 Jun 2023

Cited by 4 | Viewed by 1155

Abstract

We investigate the evolution of gravitational waves through discontinuous evolution (transition) of the Hubble expansion rate

H (z)

at a sudden cosmological singularity, which may be due to a transition of the value of the gravitational constant. We find the evolution [...] Read more.

We investigate the evolution of gravitational waves through discontinuous evolution (transition) of the Hubble expansion rate

H (z)

at a sudden cosmological singularity, which may be due to a transition of the value of the gravitational constant. We find the evolution of the scale factor and the gravitational wave waveform through the singularity by imposing the proper boundary conditions. We also use existing cosmological data and mock data of future gravitational wave experiments (the ET) to impose current and anticipated constraints on the magnitude of such a transition. We show that mock data of the Einstein Telescope can reduce the uncertainties by up to a factor of three depending on the cosmological parameter considered. Full article

(This article belongs to the Special Issue Advances in Cosmological Models)

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36 pages, 702 KiB

Open AccessReview

by Guy Chanfray, Magda Ericson and Marco Martini

Universe 2023, 9(7), 316; https://doi.org/10.3390/universe9070316 - 30 Jun 2023

Cited by 3 | Viewed by 866

Abstract

We study the role of short-range correlations, as well as pion and rho loops governing long-range RPA correlations, in nuclear matter properties and response functions. We use an adapted formulation of the Brueckner G-matrix approach to generate a pair correlation function satisfying [...] Read more.

We study the role of short-range correlations, as well as pion and rho loops governing long-range RPA correlations, in nuclear matter properties and response functions. We use an adapted formulation of the Brueckner G-matrix approach to generate a pair correlation function satisfying the Beg–Agassi–Gal theorem, providing a natural cutoff to the loop integrals. We present results for the case of a relativistic chiral theory, including the effects of quark confinement and of the chirally broken vacuum in a version where parameters are directly connected to QCD observables or constrained by well-established hadron phenomenology. This provides a unified and coherent view of the nuclear matter equation of state and the effect of correlations on neutrino–nucleus scattering. Full article

(This article belongs to the Special Issue Many Body Theory)

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41 pages, 520 KiB

Open AccessArticle

Cosmological Fluctuations in Delta Gravity

by Jorge Alfaro, Carlos Rubio and Marco San Martín

Universe 2023, 9(7), 315; https://doi.org/10.3390/universe9070315 - 30 Jun 2023

Cited by 2 | Viewed by 840

Abstract

About 70% of the Universe is Dark Energy, but the physics community still does not know what it is. Delta gravity (DG) is an alternative theory of gravitation that could solve this cosmological problem. Previously, we studied the Universe’s accelerated expansion, where DG [...] Read more.

About 70% of the Universe is Dark Energy, but the physics community still does not know what it is. Delta gravity (DG) is an alternative theory of gravitation that could solve this cosmological problem. Previously, we studied the Universe’s accelerated expansion, where DG was able to explain the SNe-Ia data successfully. In this work, we computed the cosmological fluctuations in DG that give rise to the CMB through a hydrodynamic approximation. We calculated the gauge transformations for the metric and the perfect fluid to present the equations of the evolution of cosmological fluctuations. This provided the necessary equations to solve the scalar TT power spectrum in a semi-analytical way. These equations are useful for comparing the DG theory with astronomical observations and thus being able to constrain the DG cosmology. Full article

(This article belongs to the Special Issue Universe: Feature Papers 2023—Cosmology)

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