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Universe, Volume 10, Issue 7 (July 2024) – 27 articles

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34 pages, 17772 KiB  
Article
Lorentzian Quantum Cosmology from Effective Spin Foams
by Bianca Dittrich and José Padua-Argüelles
Universe 2024, 10(7), 296; https://doi.org/10.3390/universe10070296 (registering DOI) - 13 Jul 2024
Viewed by 78
Abstract
Effective spin foams provide the most computationally efficient spin foam models yet and are therefore ideally suited for applications, e.g., to quantum cosmology. Here, we provide the first effective spin foam computations of a finite time evolution step in a Lorentzian quantum de [...] Read more.
Effective spin foams provide the most computationally efficient spin foam models yet and are therefore ideally suited for applications, e.g., to quantum cosmology. Here, we provide the first effective spin foam computations of a finite time evolution step in a Lorentzian quantum de Sitter universe. We will consider a setup that computes the no-boundary wave function and a setup describing the transition between two finite scale factors. A key property of spin foams is that they implement discrete spectra for the areas. We therefore study the effects that are induced by the discrete spectra. To perform these computations, we had to identify a technique to deal with highly oscillating and slowly converging or even diverging sums. Here, we illustrate that high-order Shanks transformation works very well and is a promising tool for the evaluation of Lorentzian (gravitational) path integrals and spin foam sums. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024—'Cosmology')
11 pages, 305 KiB  
Article
Thermodynamics of Magnetic Black Holes with Nonlinear Electrodynamics in Extended Phase Space
by Sergey Il’ich Kruglov
Universe 2024, 10(7), 295; https://doi.org/10.3390/universe10070295 (registering DOI) - 13 Jul 2024
Viewed by 96
Abstract
We study Einstein’s gravity in AdS space coupled to nonlinear electrodynamics. Thermodynamics in extended phase space of magnetically charged black holes is investigated. We compute the metric and mass functions and their asymptotics, showing that black holes may have one or two horizons. [...] Read more.
We study Einstein’s gravity in AdS space coupled to nonlinear electrodynamics. Thermodynamics in extended phase space of magnetically charged black holes is investigated. We compute the metric and mass functions and their asymptotics, showing that black holes may have one or two horizons. The metric function is regular, f(0)=1, and corrections to the Reissner–Nordström solution are in the order of O(r3) when the Schwarzschild mass is zero. We prove that the first law of black hole thermodynamics and the generalized Smarr relation hold. The magnetic potential and vacuum polarization conjugated to coupling are computed and depicted. We calculate the Gibbs free energy and the heat capacity showing that first-order and second-order phase transitions take place. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024 – Compact Objects)
12 pages, 252 KiB  
Article
On the Choice of Variable for Quantization of Conformal GR
by A. B. Arbuzov and A. A. Nikitenko
Universe 2024, 10(7), 294; https://doi.org/10.3390/universe10070294 (registering DOI) - 13 Jul 2024
Viewed by 106
Abstract
The possibility of using spin connection components as basic quantization variables of a conformal version of general relativity is studied. The considered model contains gravitational degrees of freedom and a scalar dilaton field. The standard tetrad formalism is applied. Properties of spin connections [...] Read more.
The possibility of using spin connection components as basic quantization variables of a conformal version of general relativity is studied. The considered model contains gravitational degrees of freedom and a scalar dilaton field. The standard tetrad formalism is applied. Properties of spin connections in this model are analyzed. Secondary quantization of the chosen variables is performed. The gravitational part of the model action turns out to be quadratic with respect to the spin connections. So at the quantum level, the model looks trivial, i.e., without quantum self-interactions. Meanwhile the correspondence to general relativity is preserved at the classical level. Full article
(This article belongs to the Special Issue Quantum Physics including Gravity: Highlights and Novelties)
30 pages, 2160 KiB  
Article
Isospin QCD as a Laboratory for Dense QCD
by Toru Kojo, Daiki Suenaga and Ryuji Chiba
Universe 2024, 10(7), 293; https://doi.org/10.3390/universe10070293 - 12 Jul 2024
Viewed by 157
Abstract
QCD with the isospin chemical potential μI is a useful laboratory to delineate the microphysics in dense QCD. To study the quark–hadron continuity, we use a quark–meson model that interpolates hadronic and quark matter physics at microscopic level. The equation of state [...] Read more.
QCD with the isospin chemical potential μI is a useful laboratory to delineate the microphysics in dense QCD. To study the quark–hadron continuity, we use a quark–meson model that interpolates hadronic and quark matter physics at microscopic level. The equation of state is dominated by mesons at low density but taken over by quarks at high density. We extend our previous studies with two flavors to the three-flavor case to study the impact of the strangeness, which may be brought by kaons (K+,K0)=(us¯,sd¯) and the UA(1) anomaly. In the normal phase, the excitation energies of kaons are reduced by μI in the same way as hyperons in nuclear matter at the finite baryon chemical potential. Once pions condense, kaon excitation energies increase as μI does. Moreover, strange quarks become more massive through the UA(1) coupling to the condensed pions. Hence, at zero and low temperature, the strange hadrons and quarks are highly suppressed. The previous findings in two-flavor models, sound speed peak, negative trace anomaly, gaps insensitive to μI, persist in our three-flavor model and remain consistent with the lattice results to μI 1 GeV. We discuss the non-perturbative power corrections and quark saturation effects as important ingredients to understand the crossover equations of state measured on the lattice. Full article
(This article belongs to the Special Issue Studies in Neutron Stars)
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34 pages, 1109 KiB  
Article
Stochastic Tunneling in de Sitter Spacetime
by Taiga Miyachi, Jiro Soda and Junsei Tokuda
Universe 2024, 10(7), 292; https://doi.org/10.3390/universe10070292 - 11 Jul 2024
Viewed by 193
Abstract
Tunneling processes in de Sitter spacetime are studied by using the stochastic approach. We evaluate the Martin–Siggia–Rose–Janssen–de Dominicis (MSRJD) functional integral by using the saddle-point approximation to obtain the tunneling rate. The applicability conditions of this method are clarified using the Schwinger–Keldysh formalism. [...] Read more.
Tunneling processes in de Sitter spacetime are studied by using the stochastic approach. We evaluate the Martin–Siggia–Rose–Janssen–de Dominicis (MSRJD) functional integral by using the saddle-point approximation to obtain the tunneling rate. The applicability conditions of this method are clarified using the Schwinger–Keldysh formalism. In the case of a shallow potential barrier, we reproduce the Hawking–Moss (HM) tunneling rate. Remarkably, in contrast to the HM picture, the configuration derived from the MSRJD functional integral satisfies physically natural boundary conditions. We also discuss the case of a steep potential barrier and find an interesting Coleman–de Luccia (CDL) bubblelike configuration. Since the starting point of our analysis is the Schwinger–Keldysh path integral, which can be formulated in a more generic setup and incorporates quantum effects, our formalism sheds light on further studies of tunneling phenomena from a real-time perspective. Full article
(This article belongs to the Special Issue Cosmological Models of the Universe)
28 pages, 621 KiB  
Article
Wormhole Restrictions from Quantum Energy Inequalities
by Eleni-Alexandra Kontou
Universe 2024, 10(7), 291; https://doi.org/10.3390/universe10070291 - 6 Jul 2024
Viewed by 210
Abstract
Wormhole solutions, bridges that connect different parts of spacetime, were proposed early in the history of General Relativity. Soon after, it was shown that all wormholes violate classical energy conditions, which are non-negativity constraints on contractions of the stress–energy tensor. Since these conditions [...] Read more.
Wormhole solutions, bridges that connect different parts of spacetime, were proposed early in the history of General Relativity. Soon after, it was shown that all wormholes violate classical energy conditions, which are non-negativity constraints on contractions of the stress–energy tensor. Since these conditions are violated by quantum fields, it was believed that wormholes can be constructed in the context of semiclassical gravity. But negative energies in quantum field theory are not without restriction: quantum energy inequalities (QEIs) control renormalized negative energies averaged over a geodesic. Thus, QEIs provide restrictions on the construction of wormholes. This work is a review of the relevant literature, thus focusing on results where QEIs restrict traversable wormholes. Both ‘short’ and ‘long’ (without causality violations) wormhole solutions in the context of semiclassical gravity are examined. A new result is presented on constraints on the Maldacena, Milekhin, and Popov ‘long’ wormhole from the recently derived doubled smeared null energy condition. Full article
(This article belongs to the Special Issue The Physics of Time Travel)
15 pages, 1242 KiB  
Article
Molecular Formation in Low-Metallicity Hot Cores
by Yara Sobhy, Hideko Nomura, Tetsuo Yamamoto and Osama Shalabeia
Universe 2024, 10(7), 290; https://doi.org/10.3390/universe10070290 - 4 Jul 2024
Viewed by 369
Abstract
The chemical complexity in low-metallicity hot cores has been confirmed by observations. We investigate the effect of varying physical parameters, such as temperature, density and the cosmic ray ionisation rate (CRIR), on the molecular abundance evolution in low-metallicity hot cores using the UMIST [...] Read more.
The chemical complexity in low-metallicity hot cores has been confirmed by observations. We investigate the effect of varying physical parameters, such as temperature, density and the cosmic ray ionisation rate (CRIR), on the molecular abundance evolution in low-metallicity hot cores using the UMIST gas phase chemical model. CRIR had the strongest effect on molecular abundance. The resultant molecular abundances were divided into three categories with different trends in time evolution. We compared our results with the observations of hot cores in the Large Magellanic Cloud (LMC). Our model fits best with the observations at a time of around 105 years after the evaporation of ice and at the CRIR of 1.36×1016 s1. The resultant abundances of the oxygen-bearing complex organic molecules (COMs), such as CH3OH, HCOOCH3 and CH3OCH3, do not fit with observations in the same physical condition and may be located in a different physical environment. Our results suggest that investigating the CRIR value is crucial to predict the molecular evolution in LMC hot cores. Full article
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20 pages, 486 KiB  
Article
On the Nature of the Radio Calibrator and Gamma-Ray Emitting NLS1 Galaxy 3C 286 and Its Multiwavelength Variability
by S. Komossa, S. Yao, D. Grupe and A. Kraus
Universe 2024, 10(7), 289; https://doi.org/10.3390/universe10070289 - 2 Jul 2024
Viewed by 332
Abstract
The quasar 3C 286, a well-known calibrator source in radio astronomy, was found to exhibit exceptional multiwavelength properties. Its rich and complex optical emission-line spectrum revealed its narrow-line Seyfert 1 (NLS1) nature. Given its strong radio emission, this makes 3C 286 one of [...] Read more.
The quasar 3C 286, a well-known calibrator source in radio astronomy, was found to exhibit exceptional multiwavelength properties. Its rich and complex optical emission-line spectrum revealed its narrow-line Seyfert 1 (NLS1) nature. Given its strong radio emission, this makes 3C 286 one of the radio-loudest NLS1 galaxies known to date. 3C 286 is also one of very few known compact steep-spectrum (CSS) sources detected in the gamma-ray regime. Observations in the X-ray regime, rarely carried out so far, revealed evidence for variability, raising the question whether it is driven by the accretion disk or jet. 3C 286 is also well known for its damped Lyman alpha system from an intervening absorber at z = 0.692, triggering a search for the corresponding X-ray absorption along the line-of-sight. Here, we present new observations in the radio, X-ray, optical, and UV bands. The nature of the X-ray variability is addressed. Spectral evidence suggests that it is primarily driven by the accretion disk (not the jet), and the X-ray spectrum is well fit by a powerlaw plus soft excess model. The radio flux density and polarization remain constant at the Effelsberg telescope resolution, reconfirming the use of 3C 286 as radio calibrator. The amount of reddening/absorption along the line-of-sight intrinsic to 3C 286 is rigorously assessed. None is found, validating the derivation of a high Eddington ratio (L/LEdd ∼ 1) and of the very high radio-loudness index of 3C 286. Based on the first deep Chandra image of 3C 286, tentative evidence for hard X-ray emission from the SW radio lobe is reported. A large variety of models for the gamma-ray emission of 3C 286 are briefly discussed. Full article
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13 pages, 9643 KiB  
Article
Mono-Higgs and Mono-Z Production in the Minimal Vector Dark Matter Model
by Gonzalo Benítez-Irarrázabal and Alfonso Zerwekh
Universe 2024, 10(7), 288; https://doi.org/10.3390/universe10070288 - 2 Jul 2024
Viewed by 318
Abstract
The minimal vector dark matter is a viable realization of the minimal dark matter paradigm. It extends the standard model by the inclusion of a vector matter field in the adjoint representation of SU(2)L. The dark matter candidate [...] Read more.
The minimal vector dark matter is a viable realization of the minimal dark matter paradigm. It extends the standard model by the inclusion of a vector matter field in the adjoint representation of SU(2)L. The dark matter candidate corresponds to the neutral component of the new vector field (V0). Previous studies have shown that the model can explain the observed dark matter abundance while evading direct and indirect searches. At colliders, the attention has been put on the production of the charged companions of the dark matter candidate. In this work, we focus on the mono-Higgs and mono-Z signals at Hadron colliders. The new charged vectors (V±) are invisible unless a dedicated search is performed. Consequently, we assume that the mono-Higgs and mono-Z processes correspond to the pphV+,0V,0 and ppZV+,0V,0 reactions, respectively. We show that, while the pphV+,0V,0 is more important, both channels may produce significant signals at the HL-LHC and colliders running at s=27 TeV and 100 TeV, probing almost the complete parameter space. Full article
(This article belongs to the Special Issue Search for New Physics at the LHC and Future Colliders)
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31 pages, 1771 KiB  
Article
Energetic Particles and High-Energy Processes in Cosmological Filaments and Their Astronomical Implications
by Kinwah Wu, Ellis R. Owen, Qin Han, Yoshiyuki Inoue and Lilian Luo
Universe 2024, 10(7), 287; https://doi.org/10.3390/universe10070287 - 1 Jul 2024
Viewed by 425
Abstract
Large-scale cosmic filaments connect galaxies, clusters, and voids. They are permeated by magnetic fields with a variety of topologies. Cosmic rays with energies up to 1020eV can be produced in astrophysical environments associated with star-formation and AGN activities. The fate of [...] Read more.
Large-scale cosmic filaments connect galaxies, clusters, and voids. They are permeated by magnetic fields with a variety of topologies. Cosmic rays with energies up to 1020eV can be produced in astrophysical environments associated with star-formation and AGN activities. The fate of these cosmic rays in filaments, which cannot be directly observed on Earth, are rarely studied. We investigate the high-energy processes associated with energetic particles (cosmic rays) in filaments, adopting an ecological approach that includes galaxies, clusters/superclusters, and voids as key cosmological structures in the filament ecosystem. We derive the phenomenology for modelling interfaces between filaments and these structures, and investigate how the transfer and fate of energetic cosmic ray protons are affected by the magnetism of the interfaces. We consider different magnetic field configurations in filaments and assess the implications for cosmic ray confinement and survival against hadronic pion-producing and photo-pair interactions. Our analysis shows that the fate of the particles depends on the location of their origin within a filament ecosystem, and that filaments act as ‘highways’, channelling cosmic rays between galaxies, galaxy clusters, and superclusters. Filaments can also operate as cosmic ‘fly paper’, capturing cosmic ray protons with energies up to 1018eV from cosmic voids. Our analysis predicts the presence of a population of ∼10121016eV cosmic ray protons in filaments and voids accumulated continually over cosmic time. These protons do not suffer significant energy losses through photo-pair or pion production, nor can they be cooled efficiently. Instead, they form a cosmic ray fossil record of the power generation history of the Universe. Full article
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8 pages, 407 KiB  
Article
Galaxy Group Ellipticity Confirms a Younger Cosmos
by Yu Rong
Universe 2024, 10(7), 286; https://doi.org/10.3390/universe10070286 - 29 Jun 2024
Viewed by 267
Abstract
We present an analysis of the ellipticities of galaxy groups, derived from the spatial distribution of member galaxies, revealing a notable incongruity between the observed local galaxy groups and their counterparts in the Lambda cold dark matter cosmology. Specifically, our investigation reveals a [...] Read more.
We present an analysis of the ellipticities of galaxy groups, derived from the spatial distribution of member galaxies, revealing a notable incongruity between the observed local galaxy groups and their counterparts in the Lambda cold dark matter cosmology. Specifically, our investigation reveals a substantial disparity in the ellipticities of observed groups with masses 1013.0<Mh<1014.5Mh1 exhibiting significantly higher ellipticities (at a confidence level of approximately 4σ) compared to their simulated counterparts. Notably, the consistent use of the same group finder for identifying galaxy groups in both observational and simulated datasets underscores the robustness of this result. This observation may imply a potential incongruence between the inferred age of the Universe from observations and the predictions of the model, which aligns with the younger Universe hypothesis suggested by the elevated fraction of observed satellite pairs with correlated line-of-sight relative velocities compared to simulations. Our findings significantly strengthen the plausibility of a younger age for our Universe. Full article
11 pages, 5163 KiB  
Review
X17: Status and Perspectives
by Carlo Gustavino
Universe 2024, 10(7), 285; https://doi.org/10.3390/universe10070285 - 29 Jun 2024
Viewed by 259
Abstract
Recently, a group directed by A. J. Krasznahorkay observed an anomaly in the emission of electron–positron pairs in three different nuclear reactions, namely, the 3H(p,ee+)4He, 7Li(p,ee+)8Be, and 11B(p,e [...] Read more.
Recently, a group directed by A. J. Krasznahorkay observed an anomaly in the emission of electron–positron pairs in three different nuclear reactions, namely, the 3H(p,ee+)4He, 7Li(p,ee+)8Be, and 11B(p,ee+)12C processes. Kinematics indicate that this anomaly might be due to the de-excitation of 4He, 8Be, and 12C nuclei with the emission of a boson with a mass of about 17 MeV, rapidly decaying into ee+ pairs. The result of the experiments performed with the singletron accelerator of ATOMKI is reviewed, and the consequences of the so-called X17 boson in particle physics and in cosmology are discussed. Forthcoming experiments designed to shed light on the possible existence of the X17 boson are also reported. Full article
(This article belongs to the Special Issue Recent Outcomes and Future Challenges in Nuclear Astrophysics)
26 pages, 388 KiB  
Review
Introduction to the Number of e-Folds in Slow-Roll Inflation
by Alessandro Di Marco, Emanuele Orazi and Gianfranco Pradisi
Universe 2024, 10(7), 284; https://doi.org/10.3390/universe10070284 - 29 Jun 2024
Viewed by 254
Abstract
In this review, a pedagogical introduction to the concepts of slow-roll inflationary universe and number of e-folds is provided. In particular, the differences between the basic notion of number of e-folds (Ne), total number of e-folds ( [...] Read more.
In this review, a pedagogical introduction to the concepts of slow-roll inflationary universe and number of e-folds is provided. In particular, the differences between the basic notion of number of e-folds (Ne), total number of e-folds (NT) and number of e-folds before the end of inflation (N) are outlined. The proper application of the number of e-folds before the end of inflation is discussed both as a time-like variable for the scalar field evolution and as a key parameter for computing inflationary predictions. Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024—'Cosmology')
16 pages, 413 KiB  
Article
Further Study of the Relationship between Transient Effects in Energetic Proton and Cosmic Ray Fluxes Induced by Coronal Mass Ejections
by Mihailo Savić, Nikola Veselinović, Darije Maričić, Filip Šterc, Radomir Banjanac, Miloš Travar and Aleksandar Dragić
Universe 2024, 10(7), 283; https://doi.org/10.3390/universe10070283 - 29 Jun 2024
Viewed by 294
Abstract
The study and better understanding of energetic transient phenomena caused by disturbances occurring on our Sun are of great importance, primarily due to the potential negative effects those events can have on Earth’s environment. Here, we present the continuation of our previous work [...] Read more.
The study and better understanding of energetic transient phenomena caused by disturbances occurring on our Sun are of great importance, primarily due to the potential negative effects those events can have on Earth’s environment. Here, we present the continuation of our previous work on understanding the connection between disturbances in the flux of energetic particles induced in the near-Earth environment by the passage of interplanetary coronal mass ejections and related Forbush decrease events. The relationship between the shape of fluence spectra of energetic protons measured by the instruments on the SOHO/ERNE probe at Lagrange point L1, Forbush decrease parameters measured by the worldwide network of neutron monitors, and coronal mass ejection parameters measured in situ is investigated. Various parameters used to characterize transient phenomena and their impact on the heliosphere, provided by the WIND spacecraft, were utilized to improve the accuracy of the calculation of the associated energetic proton fluence. The single and double power laws with exponential rollover were used to model the fluence spectra, and their effectiveness was compared. Correlation analysis between exponents used to characterize the shape of fluence spectra and Forbush decrease parameters is presented, and the results obtained by the two models are discussed. Full article
(This article belongs to the Section Solar System)
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13 pages, 586 KiB  
Article
The Host Galaxy Fluxes of Active Galaxy Nuclei Are Generally Overestimated by the Flux Variation Gradient Method
by Minxuan Cai, Zhen Wan, Zhenyi Cai, Lulu Fan and Junxian Wang
Universe 2024, 10(7), 282; https://doi.org/10.3390/universe10070282 - 28 Jun 2024
Viewed by 367
Abstract
In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but [...] Read more.
In terms of the variable nature of normal active galaxy nuclei (AGN) and luminous quasars, a so-called flux variation gradient (FVG) method has been widely utilized to estimate the underlying non-variable host galaxy fluxes. The FVG method assumes an invariable AGN color, but this assumption has been questioned by the intrinsic color variation of quasars and local Seyfert galaxies. Here, using an up-to-date thermal fluctuation model to simulate multi-wavelength AGN variability, we theoretically demonstrate that the FVG method generally overestimates the host galaxy flux; that is, it is more significant for brighter AGN/quasars. Furthermore, we observationally confirm that the FVG method indeed overestimates the host galaxy flux by comparing it to that estimated through other independent methods. We thus caution that applying the FVG method should be performed carefully in the era of time-domain astronomy. Full article
(This article belongs to the Special Issue Focus on Active Galactic Nuclei)
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9 pages, 253 KiB  
Communication
Quantized p-Form Gauge Field in D-Dimensional de Sitter Spacetime
by Emanuel W. D. Dantas, Geová Alencar, Ilde Guedes and Milko Estrada
Universe 2024, 10(7), 281; https://doi.org/10.3390/universe10070281 - 28 Jun 2024
Viewed by 334
Abstract
In this work, we utilize the dynamic invariant method to obtain a solution for the time-dependent Schrödinger equation, aiming to explore the quantum theory of a p-form gauge field propagating in D-dimensional de Sitter spacetimes. Thus, we present a generalization, through [...] Read more.
In this work, we utilize the dynamic invariant method to obtain a solution for the time-dependent Schrödinger equation, aiming to explore the quantum theory of a p-form gauge field propagating in D-dimensional de Sitter spacetimes. Thus, we present a generalization, through the use of p-form gauge fields, of the quantization procedure for the scalar, electromagnetic, and Kalb–Ramond fields, all of which have been previously studied in the literature. We present an exact solution for the p-form gauge field when D=2(p+1), and we highlight the connection of the p=4 case with the chiral N=2, D=10 superstring model. We could observe particle production for D2(p+1) because the solutions are time-dependent. Additionally, observers in an accelerated co-moving reference frame will also experience a thermal bath. This could have significance in the realm of extra-dimensional physics, and presents the intriguing prospect that precise observations of the Cosmic Microwave Background might confirm the presence of additional dimensions. Full article
(This article belongs to the Special Issue Quantum Physics including Gravity: Highlights and Novelties)
16 pages, 545 KiB  
Article
The cos 2ϕh Asymmetry in K± Mesons and the Λ-Hyperon-Produced SIDIS Process at Electron Ion Colliders
by Jianxi Song, Yanli Li, Shi-Chen Xue, Hui Li and Xiaoyu Wang
Universe 2024, 10(7), 280; https://doi.org/10.3390/universe10070280 - 28 Jun 2024
Viewed by 314
Abstract
We investigate the cos2ϕh azimuthal asymmetry contributed by the coupling of the Boer–Mulders function and the Collins function in K±- and Λ-hyperon-produced SIDIS process. The asymmetry is studied under the transverse-momentum-dependent (TMD) factorization framework at the leading [...] Read more.
We investigate the cos2ϕh azimuthal asymmetry contributed by the coupling of the Boer–Mulders function and the Collins function in K±- and Λ-hyperon-produced SIDIS process. The asymmetry is studied under the transverse-momentum-dependent (TMD) factorization framework at the leading order by considering the TMD evolution effects that utilize the parametrization for non-perturbative Sudakov form factors. The DGLAP evolution effects of the collinear counterpart of the Collins function of the final-state hadrons are considered by introducing the approximated evolution kernels. We utilize the available parametrization for the proton Boer–Mulders function and the Collins function of K±. For the Collins function of the Λ hyperon, the result of the diquark spectator model is adopted due to the absence of parametrization. The numerical results of the cos2ϕh azimuthal asymmetry are obtained in the kinematic regions of EIC and EicC. It can be shown that the asymmetry is much smaller than the Sivers asymmetry, which means that the convolution of the Boer–Mulders function and the Collins function may not be the main contributor to the cos2ϕh asymmetry. We emphasize the importance of future measurement of the cos2ϕh asymmetry to unravel different contributors. Full article
(This article belongs to the Special Issue The Quantum Chromodynamics: 50th Anniversary of the Discovery)
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26 pages, 2258 KiB  
Article
Reconstruction of Fermi and eROSITA Bubbles from Magnetized Jet Eruption with Simulations
by Che-Jui Chang and Jean-Fu Kiang
Universe 2024, 10(7), 279; https://doi.org/10.3390/universe10070279 - 27 Jun 2024
Viewed by 414
Abstract
The Fermi bubbles and the eROSITA bubbles around the Milky Way Galaxy are speculated to be the aftermaths of past jet eruptions from a supermassive black hole in the galactic center. In this work, a 2.5D axisymmetric relativistic magnetohydrodynamic (RMHD) model is applied [...] Read more.
The Fermi bubbles and the eROSITA bubbles around the Milky Way Galaxy are speculated to be the aftermaths of past jet eruptions from a supermassive black hole in the galactic center. In this work, a 2.5D axisymmetric relativistic magnetohydrodynamic (RMHD) model is applied to simulate a jet eruption from our galactic center and to reconstruct the observed Fermi bubbles and eROSITA bubbles. High-energy non-thermal electrons are excited around forward shock and discontinuity transition regions in the simulated plasma distributions. The γ-ray and X-ray emissions from these electrons manifest patterns on the skymap that match the observed Fermi bubbles and eROSITA bubbles, respectively, in shape, size and radiation intensity. The influence of the background magnetic field, initial mass distribution in the Galaxy, and the jet parameters on the plasma distributions and hence these bubbles is analyzed. Subtle effects on the evolution of plasma distributions attributed to the adoption of a galactic disk model versus a spiral-arm model are also studied. Full article
(This article belongs to the Special Issue Black Holes and Relativistic Jets)
9 pages, 4215 KiB  
Communication
Prospects for AGN Studies with AXIS: AGN Fueling—Resolving Hot Gas inside Bondi Radius of SMBHs
by Ka-Wah Wong, Helen R. Russell, Jimmy A. Irwin, Nico Cappelluti and Adi Foord
Universe 2024, 10(7), 278; https://doi.org/10.3390/universe10070278 - 27 Jun 2024
Viewed by 824
Abstract
Hot gas around a supermassive black hole (SMBH) should be captured within the gravitational “sphere of influence”, characterized by the Bondi radius. Deep Chandra observations have spatially resolved the Bondi radii of five nearby SMBHs that are believed to be accreting in hot [...] Read more.
Hot gas around a supermassive black hole (SMBH) should be captured within the gravitational “sphere of influence”, characterized by the Bondi radius. Deep Chandra observations have spatially resolved the Bondi radii of five nearby SMBHs that are believed to be accreting in hot accretion mode. Contrary to earlier hot accretion models that predicted a steep temperature increase within the Bondi radius, none of the resolved temperature profiles exhibit such an increase. The temperature inside the Bondi radius appears to be complex, indicative of a multi-temperature phase of hot gas with a cooler component at about 0.2–0.3 keV. The density profiles within the Bondi regions are shallow, suggesting the presence of strong outflows. These findings might be explained by recent realistic numerical simulations that suggest that large-scale accretion inside the Bondi radius can be chaotic, with cooler gas raining down in some directions and hotter gas outflowing in others. With an angular resolution similar to Chandra and a significantly larger collecting area, AXIS will collect enough photons to map the emerging accretion flow within and around the “sphere of influence” of a large sample of active galactic nuclei (AGNs). AXIS will reveal transitions in the inflow that ultimately fuels the AGN, as well as outflows that provide feedback to the environment. This White Paper is part of a series commissioned for the AXIS Probe Concept Mission; additional AXIS White Papers can be found at the AXIS website. Full article
(This article belongs to the Section Galaxies and Clusters)
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18 pages, 8494 KiB  
Article
Effects of Two Quantum Correction Parameters on Chaotic Dynamics of Particles Near Renormalized Group Improved Schwarzschild Black Holes
by Junjie Lu and Xin Wu
Universe 2024, 10(7), 277; https://doi.org/10.3390/universe10070277 - 26 Jun 2024
Viewed by 759
Abstract
A renormalized group improved Schwarzschild black hole spacetime contains two quantum correction parameters. One parameter γ represents the identification of cutoff of the distance scale, and another parameter Ω stems from nonperturbative renormalization group theory. The two parameters are constrained by the data [...] Read more.
A renormalized group improved Schwarzschild black hole spacetime contains two quantum correction parameters. One parameter γ represents the identification of cutoff of the distance scale, and another parameter Ω stems from nonperturbative renormalization group theory. The two parameters are constrained by the data from the shadow of M87* central black hole. The dynamics of electrically charged test particles around the black hole are integrable. However, when the black hole is immersed in an external asymptotically uniform magnetic field, the dynamics are not integrable and may allow for the occurrence of chaos. Employing an explicit symplectic integrator, we survey the contributions of the two parameters to the chaotic dynamical behavior. It is found that a small change of the parameter γ constrained by the shadow of M87* black hole has an almost negligible effect on the dynamical transition of particles from order to chaos. However, a small decrease in the parameter Ω leads to an enhancement in the strength of chaos from the global phase space structure. A theoretical interpretation is given to the different contributions. The term with the parameter Ω dominates the term with the parameter γ, even if the two parameters have same values. In particular, the parameter Ω acts as a repulsive force, and its decrease means a weakening of the repulsive force or equivalently enhancing the attractive force from the black hole. On the other hand, there is a positive Lyapunov exponent that is universally given by the surface gravity of the black hole when Ω ≥ 0 is small and the external magnetic field vanishes. In this case, the horizon would influence chaotic behavior in the motion of charged particles around the black hole surrounded by the external magnetic field. This point can explain why a smaller value of the renormalization group parameter would much easily induce chaos than a larger value. Full article
20 pages, 2185 KiB  
Article
Surveying the Onset and Evolution of Supermassive Black Holes at High-z with AXIS
by Nico Cappelluti, Adi Foord, Stefano Marchesi, Fabio Pacucci, Angelo Ricarte, Melanie Habouzit, Fabio Vito, Meredith Powell, Michael Koss and Richard Mushotzky
Universe 2024, 10(7), 276; https://doi.org/10.3390/universe10070276 - 25 Jun 2024
Cited by 1 | Viewed by 741
Abstract
The nature and origin of supermassive black holes (SMBHs) remain an open matter of debate within the scientific community. While various theoretical scenarios have been proposed, each with specific observational signatures, the lack of sufficiently sensitive X-ray observations hinders the progress of observational [...] Read more.
The nature and origin of supermassive black holes (SMBHs) remain an open matter of debate within the scientific community. While various theoretical scenarios have been proposed, each with specific observational signatures, the lack of sufficiently sensitive X-ray observations hinders the progress of observational tests. In this white paper, we present how AXIS will contribute to solving this issue. With an angular resolution of 1.5 on-axis and minimal off-axis degradation, we designed a deep survey capable of reaching flux limits in the [0.5–2] keV range of approximately 2 × 1018 erg s1 cm2 over an area of 0.13 deg2 in approximately 7 million seconds (7 Ms). Furthermore, we planned an intermediate depth survey covering approximately 2 deg2 and reaching flux limits of about 2 × 1017 erg s1 cm2 in order to detect a significant number of SMBHs with X-ray luminosities (LX) of approximately 1042 erg s1 up to z ∼ 10. These observations will enable AXIS to detect SMBHs with masses smaller than 105 M, assuming Eddington-limited accretion and a typical bolometric correction for Type II AGN. AXIS will provide valuable information on the seeding and population synthesis models of SMBHs, allowing for more accurate constraints on their initial mass function (IMF) and accretion history from z∼0–10. To accomplish this, AXIS will leverage the unique synergy of survey telescopes such as the JWST, Roman, Euclid, Vera Rubin Telescope, and the new generation of 30 m class telescopes. These instruments will provide optical identification and redshift measurements, while AXIS will discover the smoking gun of nuclear activity, particularly in the case of highly obscured AGN or peculiar UV spectra as predicted and recently observed by the JWST in the early Universe. Full article
(This article belongs to the Section Galaxies and Clusters)
10 pages, 580 KiB  
Article
Fitting the Crab Supernova with a Gamma-Ray Burst
by Remo Ruffini and Costantino Sigismondi
Universe 2024, 10(7), 275; https://doi.org/10.3390/universe10070275 - 25 Jun 2024
Viewed by 737
Abstract
Here, we reconsider the historical data, assuming a gamma-ray burst (GRB) as its source. A Supernova correlated with the GRB explains well the fading time observed by the ancient Chinese astronomers in the daytime and the nighttime, while the GRB power law explains [...] Read more.
Here, we reconsider the historical data, assuming a gamma-ray burst (GRB) as its source. A Supernova correlated with the GRB explains well the fading time observed by the ancient Chinese astronomers in the daytime and the nighttime, while the GRB power law explains the present X-rays and GeV emission of the Crab. On the grounds of a recent understanding of the first episode of binary-driven hypernova GRB (BDHN GRB) in terms of the collapse of a ten solar masses core, we propose the possible identification of the real Supernova event at an earlier time than Chinese chronicles. This work allows a new understanding of the significance of historical astronomical observations, including a fireball due to gamma-ray air shower observation and a plague of acute radiation syndrome, documented with several thousands of victims in the Eurasian area (Egypt, Iraq, and Syria). Full article
(This article belongs to the Section Stellar Astronomy)
15 pages, 844 KiB  
Article
Serendipitous Discovery of a 431 ms Pulsar in the Background of Westerlund 1
by Viviana Piga, Marta Burgay, Andrea Possenti, Alessandro Ridolfi, Maura Pilia, Nanda Rea, Rosalba Perna, Monica Colpi and Gianluca Israel
Universe 2024, 10(7), 274; https://doi.org/10.3390/universe10070274 - 25 Jun 2024
Viewed by 730
Abstract
We report the discovery of PSR J1646−4545, a 431 ms isolated pulsar, in the direction of the young massive cluster Westerlund 1. The pulsar was found in data taken between the years 2005 and 2010 with the “Murriyang” Parkes radio telescope in Australia. [...] Read more.
We report the discovery of PSR J1646−4545, a 431 ms isolated pulsar, in the direction of the young massive cluster Westerlund 1. The pulsar was found in data taken between the years 2005 and 2010 with the “Murriyang” Parkes radio telescope in Australia. Thanks to the numerous detections of the pulsar, we were able to derive a phase-connected timing solution spanning the whole data set. This allowed us to precisely locate the pulsar at the border of the cluster and to measure its spin-down rate. The latter implies a characteristic age of ∼25 Myr, about twice as large as the estimated age of Westerlund 1. The age of PSR J1646−4545, together with its dispersion measure of ∼1029 pc cm3, more than twice the value predicted by the two main galactic electron density models for Westerlund 1, makes the association of the pulsar with the cluster highly unlikely. We also report on ramifications from the presence of a magnetar in Westerlund 1 and the apparent lack of ordinary radio pulsars. Full article
(This article belongs to the Special Issue New Insights in Fast Radio Bursts)
27 pages, 2374 KiB  
Article
The Evolution of Galaxies and Clusters at High Spatial Resolution with Advanced X-ray Imaging Satellite (AXIS)
by Helen R. Russell, Laura A. Lopez, Steven W. Allen, George Chartas, Prakriti Pal Choudhury, Renato A. Dupke, Andrew C. Fabian, Anthony M. Flores, Kristen Garofali, Edmund Hodges-Kluck, Michael J. Koss, Lauranne Lanz, Bret D. Lehmer, Jiang-Tao Li, W. Peter Maksym, Adam B. Mantz, Michael McDonald, Eric D. Miller, Richard F. Mushotzky, Yu Qiu, Christopher S. Reynolds, Francesco Tombesi, Paolo Tozzi, Anna Trindade-Falcão, Stephen A. Walker, Ka-Wah Wong, Mihoko Yukita and Congyao Zhangadd Show full author list remove Hide full author list
Universe 2024, 10(7), 273; https://doi.org/10.3390/universe10070273 - 25 Jun 2024
Cited by 1 | Viewed by 420
Abstract
Stellar and black hole feedback heat and disperse surrounding cold gas clouds, launching gas flows off circumnuclear and galactic disks, producing a dynamic interstellar medium. On large scales bordering the cosmic web, feedback drives enriched gas out of galaxies and groups, seeding the [...] Read more.
Stellar and black hole feedback heat and disperse surrounding cold gas clouds, launching gas flows off circumnuclear and galactic disks, producing a dynamic interstellar medium. On large scales bordering the cosmic web, feedback drives enriched gas out of galaxies and groups, seeding the intergalactic medium with heavy elements. In this way, feedback shapes galaxy evolution by shutting down star formation and ultimately curtailing the growth of structure after the peak at redshift 2–3. To understand the complex interplay between gravity and feedback, we must resolve both the key physics within galaxies and map the impact of these processes over large scales, out into the cosmic web. The Advanced X-ray Imaging Satellite (AXIS) is a proposed X-ray probe mission for the 2030s with arcsecond spatial resolution, large effective area, and low background. AXIS will untangle the interactions of winds, radiation, jets, and supernovae with the surrounding interstellar medium across the wide range of mass scales and large volumes driving galaxy evolution and trace the establishment of feedback back to the main event at cosmic noon. This white paper is part of a series commissioned for the AXIS Probe mission concept; additional AXIS white papers can be found at the AXIS website. Full article
(This article belongs to the Section Galaxies and Clusters)
17 pages, 570 KiB  
Article
FLRW Transit Cosmological Model in f(R,T) Gravity
by Vijay Singh, Siwaphiwe Jokweni and Aroonkumar Beesham
Universe 2024, 10(7), 272; https://doi.org/10.3390/universe10070272 - 24 Jun 2024
Viewed by 405
Abstract
A Friedmann–Lemaitre–Robertson–Walker space–time model with all curvatures k=0,±1 is explored in f(R,T) gravity, where R is the Ricci scalar, and T is the trace of the energy–momentum tensor. The solutions are obtained via [...] Read more.
A Friedmann–Lemaitre–Robertson–Walker space–time model with all curvatures k=0,±1 is explored in f(R,T) gravity, where R is the Ricci scalar, and T is the trace of the energy–momentum tensor. The solutions are obtained via the parametrization of the scale factor that leads to a model transiting from a decelerated universe to an accelerating one. The physical features of the model are discussed and analyzed in detail. The study shows that f(R,T) gravity can be a good alternative to the hypothetical candidates of dark energy to describe the present accelerating expansion of the universe. Full article
(This article belongs to the Special Issue The Friedmann Cosmology: A Century Later)
6 pages, 220 KiB  
Communication
The de Sitter Swampland Conjectures in the Context of Chaplygin-Inspired Inflation
by Orfeu Bertolami, Robertus Potting and Paulo M. Sá
Universe 2024, 10(7), 271; https://doi.org/10.3390/universe10070271 - 23 Jun 2024
Viewed by 320
Abstract
In this work, we discuss the de Sitter swampland conjectures in the context of the generalized Chaplygin-inspired inflationary model. We demonstrate that these conjectures can be satisfied, but only in the region of the parameter space far away from the General Relativity limit. [...] Read more.
In this work, we discuss the de Sitter swampland conjectures in the context of the generalized Chaplygin-inspired inflationary model. We demonstrate that these conjectures can be satisfied, but only in the region of the parameter space far away from the General Relativity limit. The cosmic microwave background data had already been found to restrict the allowed inflationary potentials of this model. Our results impose a further limitation on the possible potentials. Full article
25 pages, 518 KiB  
Article
Non-Minimally Coupled Electromagnetic Fields and Observable Implications for Primordial Black Holes
by Susmita Jana and S. Shankaranarayanan
Universe 2024, 10(7), 270; https://doi.org/10.3390/universe10070270 - 22 Jun 2024
Cited by 3 | Viewed by 319
Abstract
General relativity (GR) postulates have been verified with high precision, yet our understanding of how gravity interacts with matter fields remains incomplete. Various modifications to GR have been proposed in both classical and quantum realms to address these interactions within the strong gravity [...] Read more.
General relativity (GR) postulates have been verified with high precision, yet our understanding of how gravity interacts with matter fields remains incomplete. Various modifications to GR have been proposed in both classical and quantum realms to address these interactions within the strong gravity regime. One such approach is non-minimal coupling (NMC), where the space-time curvature (scalar and tensor) interacts with matter fields, resulting in matter fields not following the geodesics. To probe the astrophysical implications of NMC, in this work, we investigate non-minimally coupled electromagnetic (EM) fields in the presence of black holes. Specifically, we show that primordial black holes (PBHs) provide a possible tool to constrain the NMC parameter. PBHs represent an intriguing cosmological black hole class that does not conform to the no-hair theorem. We model the PBH as a Sultana–Dyer black hole and compare it with Schwarzschild. We examine observables such as the radius of the photon sphere, critical impact parameter, and total deflection angles for non-minimally coupled photons for Schwarzschild and Sultana–Dyer black holes. Both the black hole space-times lead to similar constraints on the NMC parameter. For a PBH of mass M=105M, the photon sphere will not be formed for one mode. Hence, the photons forming the photon sphere will be highly polarized, potentially leading to observable implications. Full article
(This article belongs to the Collection Open Questions in Black Hole Physics)
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