Congratulations to Prof. Roger Penrose, Advisory Board member of Universe, for receiving the Nobel Prize in Physics 2020.
Journal Description
Universe
Universe
is a peer-reviewed open access journal focused on principles and new discoveries in the universe. Universe is published monthly online by MDPI.
- Open Access— free for readers, with article processing charges (APC) paid by authors or their institutions.
- High Visibility: indexed within Scopus, SCIE (Web of Science), Astrophysics Data System, INSPIRE, CAPlus / SciFinder, Inspec, and other databases.
- Journal Rank: JCR - Q2 (Astronomy & Astrophysics) / CiteScore - Q2 (General Physics and Astronomy)
- Rapid Publication: manuscripts are peer-reviewed and a first decision is provided to authors approximately 20.6 days after submission; acceptance to publication is undertaken in 2.9 days (median values for papers published in this journal in the second half of 2023).
- Recognition of Reviewers: reviewers who provide timely, thorough peer-review reports receive vouchers entitling them to a discount on the APC of their next publication in any MDPI journal, in appreciation of the work done.
- Companion journal: Astronomy.
Impact Factor:
2.9 (2022);
5-Year Impact Factor:
2.4 (2022)
Latest Articles
Gravitational Wormholes
Universe 2024, 10(6), 257; https://doi.org/10.3390/universe10060257 (registering DOI) - 10 Jun 2024
Abstract
Spacetime wormholes are evidently an essential component of the construction of a time machine. Within the context of general relativity, such objects require, for their formation, exotic matter—matter that violates at least one of the standard energy conditions. Here, we explore the possibility
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Spacetime wormholes are evidently an essential component of the construction of a time machine. Within the context of general relativity, such objects require, for their formation, exotic matter—matter that violates at least one of the standard energy conditions. Here, we explore the possibility that higher-curvature gravity theories might permit the construction of a wormhole without any matter at all. In particular, we consider the simplest form of a generalized quasi topological theory in four spacetime dimensions, known as Einsteinian Cubic Gravity. This theory has a number of promising features that make it an interesting phenomenological competitor to general relativity, including having non-hairy generalizations of the Schwarzschild black hole and linearized equations of second order around maximally symmetric backgrounds. By matching series solutions near the horizon and at large distances, we find evidence that strong asymptotically AdS wormhole solutions can be constructed, with strong curvature effects ensuring that the wormhole throat can exist.
Full article
(This article belongs to the Special Issue The Physics of Time Travel)
Open AccessReview
The Hearth of the World: The Sun before Astrophysics
by
Gábor Kutrovátz
Universe 2024, 10(6), 256; https://doi.org/10.3390/universe10060256 - 7 Jun 2024
Abstract
This paper presents a historical overview of conceptions about the Sun in Western astronomical and cosmological traditions before the advent of spectroscopy and astrophysics. Rather than studying general cultural ideas, we focus on the concepts developed by astronomers or by natural philosophers impacting
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This paper presents a historical overview of conceptions about the Sun in Western astronomical and cosmological traditions before the advent of spectroscopy and astrophysics. Rather than studying general cultural ideas, we focus on the concepts developed by astronomers or by natural philosophers impacting astronomy. The ideas we investigate, from the works of Plato and Aristotle to William Herschel and his contemporaries, do not line up into a continuous and integrated narrative, since the nature of the Sun was not a genuine scientific topic before the nineteenth century. However, the question recurringly arose as embedded in cosmological and physical contexts. By outlining this heterogeneous story that spreads from transcendence to materiality, from metaphysics to physics, from divinity to solar inhabitants, we receive insight into some major themes and trends both in the general development of astronomical and cosmological thought and in the prehistory of modern solar science.
Full article
(This article belongs to the Special Issue Solar and Stellar Activity: Exploring the Cosmic Nexus)
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Open AccessCommunication
The Pulsar Timing Array Signal from Infrared Regions of Scalar-Induced Gravitational Waves
by
Qin Fei
Universe 2024, 10(6), 255; https://doi.org/10.3390/universe10060255 - 7 Jun 2024
Abstract
The common-spectrum process, characterized by the Hellings–Downs angular correlation and observed by pulsar timing array collaborations, such as NANOGrav, PPTA, EPTA, and CPTA, can be explained by the scalar-induced gravitational waves (SIGWs). The energy density of SIGWs exhibits universal behavior in the infrared
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The common-spectrum process, characterized by the Hellings–Downs angular correlation and observed by pulsar timing array collaborations, such as NANOGrav, PPTA, EPTA, and CPTA, can be explained by the scalar-induced gravitational waves (SIGWs). The energy density of SIGWs exhibits universal behavior in the infrared regions. Utilizing a broken power law parameterization for the primordial curvature power spectrum, we clarify the PTA signal through the infrared characteristics of the SIGWs, using Bayesian analysis to provide posterior distributions. Bayesian factors emphasize the statistical preference for the SIGW model over explanations involving supermassive black hole binaries.
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(This article belongs to the Section Cosmology)
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Open AccessReview
The Correlation Luminosity-Velocity Dispersion of Galaxies and Active Galactic Nuclei
by
Mauro D’Onofrio, Paola Marziani, Cesare Chiosi and Castalia Alenka Negrete
Universe 2024, 10(6), 254; https://doi.org/10.3390/universe10060254 - 4 Jun 2024
Abstract
In this work we discuss the correlation between luminosity L and velocity dispersion observed in different astrophysical contexts, in particular that of early-type galaxies (ETGs; Faber–Jackson (FJ) law) and that of active galactic nuclei (AGN). Our data for the ETGs confirm the
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In this work we discuss the correlation between luminosity L and velocity dispersion observed in different astrophysical contexts, in particular that of early-type galaxies (ETGs; Faber–Jackson (FJ) law) and that of active galactic nuclei (AGN). Our data for the ETGs confirm the bending of the FJ at high masses and the existence of similar curvatures in the projections of the Fundamental Plane (FP) approximately at the mass scale of ∼ . We provide an explanation for such curvatures and for the presence of the Zone of Exclusion (ZoE) in these diagrams. The new prospected theory for the FJ law introduces a new framework to understand galaxy evolution in line with the hierarchical structure of the Universe. The classic analysis carried out for a class of type 1 AGN accreting gas at very high rates, confirms that a FJ law of the form is roughly consistent with the observations, with a slope quite similar to that of ETGs. We discuss the physics behind the FJ law for the AGN in different contexts and also examine the biases affecting both the luminosity and the velocity dispersion, paying particular attention to the effects induced by the spherical symmetry of the emitting sources on the accuracy of the luminosity estimates.
Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024—"Galaxies and Clusters")
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Open AccessArticle
Cosmic Strings from Thermal Inflation
by
Robert Brandenberger and Aline Favero
Universe 2024, 10(6), 253; https://doi.org/10.3390/universe10060253 - 4 Jun 2024
Abstract
Thermal inflation was proposed as a mechanism to dilute the density of cosmological moduli. Thermal inflation is driven by a complex scalar field possessing a large vacuum expectation value and a very flat potential, called a “flaton”. Such a model admits cosmic string
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Thermal inflation was proposed as a mechanism to dilute the density of cosmological moduli. Thermal inflation is driven by a complex scalar field possessing a large vacuum expectation value and a very flat potential, called a “flaton”. Such a model admits cosmic string solutions, and a network of such strings will inevitably form in the symmetry breaking phase transition at the end of the period of thermal inflation. We discuss the differences of these strings compared to the strings which form in the Abelian Higgs model. Specifically, we find that the upper bound on the symmetry breaking scale is parametrically lower than in the case of Abelian Higgs strings, and that the lower cutoff on the string loop distribution is determined by cusp annihilation rather than by gravitational radiation (for the value of the transition temperature proposed in the original work on thermal inflation).
Full article
(This article belongs to the Special Issue Origins and Natures of Inflation, Dark Matter and Dark Energy, 2nd Edition)
Open AccessArticle
Improved Statistical Analysis for the Neutrinoless Double-Beta Decay Matrix Element of 136Xe
by
Mihai Horoi
Universe 2024, 10(6), 252; https://doi.org/10.3390/universe10060252 - 4 Jun 2024
Abstract
Neutrinoless double beta decay nuclear matrix element ( ) for 136Xe was recently analyzed using a statistical approach (Phys. Rev. C 107, 045501 (2023)). In the analysis, three initial shell model effective Hamiltonians were randomly altered, and their
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Neutrinoless double beta decay nuclear matrix element ( ) for 136Xe was recently analyzed using a statistical approach (Phys. Rev. C 107, 045501 (2023)). In the analysis, three initial shell model effective Hamiltonians were randomly altered, and their results for 23 measured observables were used to infer credibility for the nuclear matrix element (NME) based on a Bayesian Model Averaging approach. In that analysis, a reasonable Gamow-Teller quenching factor of 0.7 was assumed for each starting effective Hamiltonian. Given that the result of the statistical analysis was sensible to this choice, we are here improving that analysis by assuming that the Gamow-Teller quenching factor is also randomly chosen within reasonabe limits for all three starting Hamiltonians. The outcomes are slightly higher expectation values and uncertainties for the NME.
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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Open AccessCommunication
Constraints on the Primordial Curvature Power Spectrum and Reheating Temperature from the NANOGrav 15-Year Dataset
by
Qin Fei
Universe 2024, 10(6), 251; https://doi.org/10.3390/universe10060251 - 4 Jun 2024
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The stochastic signal observed by collaborations such as NANOGrav, PPTA, EPTA +InPTA, and CPTA may originate from gravitational waves induced by primordial curvature perturbations during inflation. This study investigates small-scale properties of inflation and reheating, assuming a log-normal form for the power spectrum
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The stochastic signal observed by collaborations such as NANOGrav, PPTA, EPTA +InPTA, and CPTA may originate from gravitational waves induced by primordial curvature perturbations during inflation. This study investigates small-scale properties of inflation and reheating, assuming a log-normal form for the power spectrum of the primordial curvature and a reheating phase equation of state . Inflation and reheating scenarios are thoroughly examined using Bayesian methods applied to the NANOGrav 15-year dataset. The analysis establishes constraints on the reheating temperature, suggesting , consistent with Big Bang nucleosynthesis constraints. Additionally, the NANOGrav 15-year dataset requires the amplitude (A∼0.1) and width ( ) of the primordial curvature power spectrum to be within specific ranges. A notable turning point in the energy density of scalar-induced gravitational waves occurs due to a change in the equation of state w. This turning point signifies a transition from the reheating epoch to radiation domination. Further observations of scalar-induced gravitational waves could provide insights into the precise timing of this transition, enhancing our understanding of early Universe dynamics.
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Open AccessArticle
Rotation Matrix of a Charged Symmetrical Body: One-Parameter Family of Solutions in Elementary Functions
by
Alexei A. Deriglazov
Universe 2024, 10(6), 250; https://doi.org/10.3390/universe10060250 - 3 Jun 2024
Abstract
Euler–Poisson equations of a charged symmetrical body in external constant and homogeneous electric and magnetic fields are deduced starting from the variational problem, where the body is considered as a system of charged point particles subject to holonomic constraints. The final equations are
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Euler–Poisson equations of a charged symmetrical body in external constant and homogeneous electric and magnetic fields are deduced starting from the variational problem, where the body is considered as a system of charged point particles subject to holonomic constraints. The final equations are written for the center-of-mass coordinate, rotation matrix and angular velocity. A general solution to the equations of motion is obtained for the case of a charged ball. For the case of a symmetrical charged body (solenoid), the task of obtaining the general solution is reduced to the problem of a one-dimensional cubic pseudo-oscillator. In addition, we present a one-parametric family of solutions to the problem in elementary functions.
Full article
Open AccessArticle
On the Role of the Tail Term in Electromagnetic Radiation Reaction
by
Zdeněk Stuchlík, Martin Kološ, Arman Tursunov and Dmitri Gal’tsov
Universe 2024, 10(6), 249; https://doi.org/10.3390/universe10060249 - 3 Jun 2024
Abstract
In a recent study devoted to the influence of electromagnetic radiation reaction on the motion of radiating charged particles in magnetized black hole spacetimes the authors claim that the tail term cannot be neglected in the complete DeWitt–Brehme equation, putting into doubt the
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In a recent study devoted to the influence of electromagnetic radiation reaction on the motion of radiating charged particles in magnetized black hole spacetimes the authors claim that the tail term cannot be neglected in the complete DeWitt–Brehme equation, putting into doubt the previous papers where such an approximation was used. Here, we demonstrate by using simple dimensional arguments that such a statement is misleading in many astrophysically relevant situations. In the case of relativistic electrons moving around a stellar-mass black hole, the tail term is ignorable if a magnetic field of at least a few Gauss is present.On the other hand, in different situations, the tail term can be relevant, as demonstrated in the case of orbital widening, where it can even amplify the effect.
Full article
(This article belongs to the Collection Open Questions in Black Hole Physics)
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Open AccessReview
Decoding the Nature of Coherent Radio Emission in Pulsars I: Observational Constraints
by
Dipanjan Mitra, Rahul Basu and George I. Melikizde
Universe 2024, 10(6), 248; https://doi.org/10.3390/universe10060248 - 3 Jun 2024
Abstract
Radio observations from normal pulsars indicate that the coherent radio emission is excited by curvature radiation from charge bunches. In this review, we provide a systematic description of the various observational constraints on the radio emission mechanism. We have discussed the presence of
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Radio observations from normal pulsars indicate that the coherent radio emission is excited by curvature radiation from charge bunches. In this review, we provide a systematic description of the various observational constraints on the radio emission mechanism. We have discussed the presence of highly polarized time samples where the polarization position angle follow two orthogonal well-defined tracks across the profile that closely match the rotating vector model in an identical manner. The observations also show the presence of circular polarization, with both the right and left handed circular polarization seen across the profile. Other constraints on the emission mechanism are provided by the detailed measurements of the spectral index variation across the profile window, where the central part of the profile, corresponding to the core component, has a steeper spectrum than the surrounding cones. Finally, the detailed measurements of the subpulse drifting behaviour can be explained by considering the presence of non-dipolar field on the stellar surface and the formation of the partially screened gap (PSG) above the polar cap region. The PSG gives rise to a non-stationary plasma flow that has a multi-component nature, consisting of highly energetic primary particles, secondary pair plasma, and iron ions discharged from the surface, with large fragmentation resulting in dense plasma clouds and lower-density inter-cloud regions. The physical properties of the outflowing plasma and the observational constraints lead us to consider coherent curvature radiation as the most viable explanation for the emission mechanism in normal pulsars, where propagation effects due to adiabatic walking and refraction are largely inconsequential.
Full article
(This article belongs to the Special Issue A New Horizon of Pulsar and Neutron Star: The 55-Year Anniversary)
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Open AccessReview
Neutrino Masses and Right-Handed Weak Currents Studied by Neutrino-Less ββ-Decay Detectors
by
Saori Umehara and Hiroyasu Ejiri
Universe 2024, 10(6), 247; https://doi.org/10.3390/universe10060247 - 3 Jun 2024
Abstract
Detecting neutrino-less double beta ( ) decay with high-sensitivity detectors is of current interest for studying the Majorana neutrino’s nature, the neutrino mass ( -mass), right-handed weak currents (RHCs), and others beyond the Standard
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Detecting neutrino-less double beta ( ) decay with high-sensitivity detectors is of current interest for studying the Majorana neutrino’s nature, the neutrino mass ( -mass), right-handed weak currents (RHCs), and others beyond the Standard Model. Many experimental groups have studied decay with -mass sensitivities on the order of 100 meV and RHC sensitivities on the order of 10 –10 , but no clear signals have been observed so far in these -mass and RHC regions. Thus, several experimental groups are developing higher-sensitivity detectors to explore a smaller -mass region around 15–50 meV, which corresponds to the inverted hierarchy -mass, and smaller RHC regions on the order of 10 –10 in the near future. Nuclear matrix elements (NMEs) for -mass and RHC processes are crucial for extracting the -mass and RHCs of particle physics interest from experiments. This report briefly reviews detector sensitivities and upper limits on the -mass and right-handed currents for several current detectors and the -mass and RHC sensitivities expected for some near-future ones.
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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Open AccessArticle
New Parametrization of the Dark-Energy Equation of State with a Single Parameter
by
Jainendra Kumar Singh, Preeti Singh, Emmanuel N. Saridakis, Shynaray Myrzakul and Harshna Balhara
Universe 2024, 10(6), 246; https://doi.org/10.3390/universe10060246 - 1 Jun 2024
Abstract
We propose a novel dark-energy equation-of-state parametrization, with a single parameter that quantifies the deviation from ΛCDM cosmology. We first confront the scenario with various datasets, from the Hubble function (OHD), Pantheon, baryon acoustic oscillations (BAO), and their joint observations, and we
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We propose a novel dark-energy equation-of-state parametrization, with a single parameter that quantifies the deviation from ΛCDM cosmology. We first confront the scenario with various datasets, from the Hubble function (OHD), Pantheon, baryon acoustic oscillations (BAO), and their joint observations, and we show that has a preference for a non-zero value, namely, a deviation from ΛCDM cosmology is favored, although the zero value is marginally inside the 1 confidence level. However, we find that the present Hubble function value acquires a higher value, namely, Km s Mpc , which implies that the tension can be partially alleviated. Additionally, we perform a cosmographic analysis, showing that the universe transits from deceleration to acceleration in the recent cosmological past; nevertheless, in the future, it will not result in a de Sitter phase since it exhibits a second transition from acceleration to deceleration. Finally, we perform the statefinder analysis. The scenario behaves similarly to the ΛCDM paradigm at high redshifts, while the deviation becomes significant at late and recent times and especially in the future.
Full article
(This article belongs to the Collection Modified Theories of Gravity and Cosmological Applications)
Open AccessCommunication
X-ray Redshifts for Obscured Active Galactic Nuclei with AXIS Deep and Intermediate Surveys
by
Alessandro Peca, Nico Cappelluti, Stefano Marchesi, Edmund Hodges-Kluck and Adi Foord
Universe 2024, 10(6), 245; https://doi.org/10.3390/universe10060245 - 1 Jun 2024
Abstract
This study presents the capabilities of the AXIS telescope in estimating redshifts from X-ray spectra alone (X-ray redshifts, XZs). Through extensive simulations, we establish that AXIS observations enable reliable XZ estimates for more than 5500 obscured active galactic nuclei (AGNs) up to redshift
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This study presents the capabilities of the AXIS telescope in estimating redshifts from X-ray spectra alone (X-ray redshifts, XZs). Through extensive simulations, we establish that AXIS observations enable reliable XZ estimates for more than 5500 obscured active galactic nuclei (AGNs) up to redshift in the proposed deep (7 Ms) and intermediate (375 ks) surveys. Notably, at least 1600 of them are expected to be in the Compton-thick regime ( ), underscoring the pivotal role of AXIS in sampling these elusive objects that continue to be poorly understood. XZs provide an efficient alternative for optical/infrared faint sources, overcoming the need for time-consuming spectroscopy, the potential limitations of photometric redshifts, and potential issues related to multi-band counterpart association. This approach will significantly enhance the accuracy of constraints on the X-ray luminosity function and obscured AGN fractions up to high redshifts. 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)
Open AccessArticle
Charmonium Transport in Heavy-Ion Collisions at the LHC
by
Biaogang Wu and Ralf Rapp
Universe 2024, 10(6), 244; https://doi.org/10.3390/universe10060244 - 31 May 2024
Abstract
We provide an update on our semi-classical transport approach for quarkonium production in high-energy heavy-ion collisions, focusing on and mesons in 5.02 TeV Pb-Pb collisions at the Large Hadron Collider (LHC) at both forward and
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We provide an update on our semi-classical transport approach for quarkonium production in high-energy heavy-ion collisions, focusing on and mesons in 5.02 TeV Pb-Pb collisions at the Large Hadron Collider (LHC) at both forward and mid-rapidity. In particular, we employ the most recent charm-production cross sections reported in pp collisions, which are pivotal for the magnitude of the regeneration contribution, and their modifications due to cold-nuclear-matter (CNM) effects. Multi-differential observables are calculated in terms of nuclear modification factors as a function of centrality, transverse momentum, and rapidity, including the contributions from feeddown from bottom hadron decays. For our predictions for production, the mechanism of sequential regeneration relative to the more strongly bound meson plays an important role in interpreting recent ALICE data.
Full article
(This article belongs to the Special Issue Universe: Feature Papers 2024—High Energy Nuclear and Particle Physics)
Open AccessCommunication
Search for R-Parity-Violation-Induced Charged Lepton Flavor Violation at Future Lepton Colliders
by
Xunye Cai, Jingshu Li, Ran Ding, Meng Lu, Zhengyun You and Qiang Li
Universe 2024, 10(6), 243; https://doi.org/10.3390/universe10060243 - 31 May 2024
Abstract
Interest in searches for Charged Lepton Flavor Violation (CLFV) has continued in the past few decades since the observation of CLFV would indicate a new physics Beyond the Standard Model (BSM). As several future lepton colliders with high luminosity have been proposed, the
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Interest in searches for Charged Lepton Flavor Violation (CLFV) has continued in the past few decades since the observation of CLFV would indicate a new physics Beyond the Standard Model (BSM). As several future lepton colliders with high luminosity have been proposed, the search for CLFV will reach an unprecedented level of precision. Many BSM models allow CLFV processes at the tree level, such as the R-parity-violating (RPV) Minimal Supersymmetric Standard Model (MSSM), which is a good choice for benchmarking. In this paper, we perform a detailed fast Monte Carlo simulation study on RPV-induced CLFV processes at future lepton colliders, including a 240 circular electron positron collider (CEPC) and a 6 or 14 Muon Collider. As a result, we found that the upper limits on the -related RPV couplings will be significantly improved, while several new limits on RPV couplings can be set, which are inaccessible by low-energy experiments.
Full article
(This article belongs to the Special Issue Search for New Physics at the LHC and Future Colliders)
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Open AccessArticle
Optical Quasi-Periodic Oscillation of Blazar PKS 1440-389 in the TESS Light Curve
by
He Lu, Tingfeng Yi, Yanke Tang, Junjie Wang, Shun Zhang, Liang Wang, Yutong Chen, Yuncai Shen, Liang Dong and Yangwei Zhang
Universe 2024, 10(6), 242; https://doi.org/10.3390/universe10060242 - 31 May 2024
Abstract
We report the results of time series analysis of blazar PKS 1440-389, observed by the Transiting Exoplanet Survey Satellite (TESS) in two sectors. We find that the source has a quasi-periodic oscillation (QPO) of about 3.1 days for sector 11 and around 3.7
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We report the results of time series analysis of blazar PKS 1440-389, observed by the Transiting Exoplanet Survey Satellite (TESS) in two sectors. We find that the source has a quasi-periodic oscillation (QPO) of about 3.1 days for sector 11 and around 3.7 days for sector 38 in the optical band. We use two methods to assess the QPO and its confidence level: Lomb–Scargle periodogram and weighted wavelet Z-transforms. We explore various potential explanations for these rapid quasi-periodic variations and propose that their source most likely resides within the innermost region of the accretion disk. Within this framework, we estimate the mass of the central black hole of this blazar. We obtain black hole masses of 6.65 × 108 (Schwarzschild black hole) and 4.22 × 109 (maximally rotating Kerr black hole), with a main period of 3.7 days. Finally, we utilize the kink instability model to explain the QPO.
Full article
(This article belongs to the Special Issue Blazar Bursts: Theory and Observation)
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Open AccessArticle
Mechanisms for Producing Primordial Black Holes from Inflationary Models beyond Fine-Tuning
by
Ioanna Stamou
Universe 2024, 10(6), 241; https://doi.org/10.3390/universe10060241 - 30 May 2024
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In this study, we present an analysis of the fine-tuning required in various inflationary models in order to explain the production of Primordial Black Holes (PBHs). We specifically examine the degree of fine-tuning necessary in two prominent single-field inflationary models: those with an
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In this study, we present an analysis of the fine-tuning required in various inflationary models in order to explain the production of Primordial Black Holes (PBHs). We specifically examine the degree of fine-tuning necessary in two prominent single-field inflationary models: those with an inflection point and those with step-like features in the potential. Our findings indicate that models with step-like features generally require less fine-tuning compared to those with an inflection point, making them more viable for consistent PBH production. An interesting outcome of these models is that, in addition to improved fine-tuning, they may also predict low-frequency signals that can be detected by pulsar timing array (PTA) collaborations. Additionally, we extend our analysis to multifield inflationary models to assess whether the integration of additional fields can further alleviate the fine-tuning demands. The study also explores the role of a spectator field and its impact on the fine-tuning process. Our results indicate that although mechanisms involving a spectator field can circumvent the issue of fine-tuning parameters for PBH production, both multifield models and models with step-like features present promising alternatives. While fine-tuning involves multiple considerations, our primary objective is to evaluate various inflationary models to identify the one that most naturally explains the formation of PBHs. Hence, this study introduces a novel approach by categorizing existing PBH mechanisms, paving the way for subsequent research to prioritize models that minimize the need for extensive fine-tuning.
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Open AccessArticle
Renormalization Analysis of Magnetohydrodynamics: Two-Loop Approximation
by
Michal Hnatič, Tomáš Lučivjanský, Lukáš Mižišin, Yurii Molotkov and Andrei Ovsiannikov
Universe 2024, 10(6), 240; https://doi.org/10.3390/universe10060240 - 30 May 2024
Abstract
We investigate the stochastic version of the paradigmatic model of magnetohydrodynamic turbulence. The model can be interpreted as an active vector admixture subject to advective processes governed by turbulent flow. The back influence on fluid dynamics is explicitly taken into account. The velocity
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We investigate the stochastic version of the paradigmatic model of magnetohydrodynamic turbulence. The model can be interpreted as an active vector admixture subject to advective processes governed by turbulent flow. The back influence on fluid dynamics is explicitly taken into account. The velocity field is generated through a fully developed turbulent flow taking into account the violation of spatial parity, which is introduced through the helicity parameter . We consider a generalized setup in which parameter A is introduced in model formulation, which is associated with the interaction part of the model, and its actual value represents different physical systems. The model is analyzed by means of the field-theoretic renormalization group. The calculation is performed using -expansion, where is the deviation from the Kolmogorov scaling. Two-loop numerical calculations of the renormalization constant associated with the renormalization of the magnetic field are presented.
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(This article belongs to the Section Field Theory)
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Open AccessArticle
Inflaton Decay in No-Scale Supergravity and Starobinsky-like Models
by
Yohei Ema, Marcos A. G. Garcia, Wenqi Ke, Keith A. Olive and Sarunas Verner
Universe 2024, 10(6), 239; https://doi.org/10.3390/universe10060239 - 30 May 2024
Abstract
We consider the decay of the inflaton in Starobinsky-like models arising from either an theory of gravity or no-scale supergravity models. If Standard Model matter is simply introduced to the theory, the
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We consider the decay of the inflaton in Starobinsky-like models arising from either an theory of gravity or no-scale supergravity models. If Standard Model matter is simply introduced to the theory, the inflaton (which appears when the theory is conformally transformed into the Einstein frame) couples to matter predominantly in Standard Model Higgs kinetic terms. This will typically lead to a reheating temperature of ∼3 × GeV. However, if the Standard Model Higgs is conformally coupled to curvature, the decay rate may be suppressed and vanishes for conformal coupling . Nevertheless, the inflaton decays through the conformal anomaly, leading to a reheating temperature of the order of GeV. The Starobinsky potential may also arise in no-scale supergravity. In this case, the inflaton decays if there is a direct coupling of the inflaton to matter in the superpotential or to gauge fields through the gauge kinetic function. We also discuss the relation between the theories and demonstrate the correspondence between the no-scale models and the conformally coupled theory (with ).
Full article
(This article belongs to the Special Issue Particle Physics and Cosmology: A Themed Issue in Honor of Professor Dimitri Nanopoulos)
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Open AccessReview
Supernova Neutrinos: Flavour Conversion Mechanisms and New Physics Scenarios
by
Manibrata Sen
Universe 2024, 10(6), 238; https://doi.org/10.3390/universe10060238 - 30 May 2024
Abstract
A core-collapse supernova (SN) releases almost all of its energy in the form of neutrinos, which provide a unique opportunity to probe the working machinery of an SN. These sites are prone to neutrino–neutrino refractive effects, which can lead to fascinating collective flavour
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A core-collapse supernova (SN) releases almost all of its energy in the form of neutrinos, which provide a unique opportunity to probe the working machinery of an SN. These sites are prone to neutrino–neutrino refractive effects, which can lead to fascinating collective flavour oscillations among neutrinos. This causes rapid neutrino flavour conversions deep inside the SN even for suppressed mixing angles, with intriguing consequences for the explosion mechanism as well as nucleosynthesis. We review the physics of collective oscillations of neutrinos—both slow and fast—along with the well-known resonant flavour conversion effects and discuss the current state-of-the-art of the field. Furthermore, we discuss how neutrinos from an SN can be used to probe novel particle physics properties, extreme values of which are otherwise inaccessible in laboratories.
Full article
(This article belongs to the Special Issue Neutrinos across Different Energy Scales)
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Topic in
Entropy, Galaxies, Quantum Reports, Symmetry, Universe
Covariance, Objectivity and Evolution Equations in Either Classical or Quantum Gravity and Quantum Mechanics
Topic Editors: Massimo Tessarotto, Claudio CremaschiniDeadline: 20 October 2024
Topic in
IJMS, Pharmaceutics, Cells, Biomolecules, Plants, Universe, Cancers, Antioxidants
Advances in Astrobiology
Topic Editors: Massimo Maffei, Barbara Cavalazzi, Marta del BiancoDeadline: 30 November 2024
Topic in
Aerospace, Applied Sciences, Remote Sensing, Sensors, Universe, Data
Techniques and Science Exploitations for Earth Observation and Planetary Exploration
Topic Editors: Yu Tao, Siting Xiong, Rui SongDeadline: 31 March 2025
Conferences
Special Issues
Special Issue in
Universe
Small-Scale Eruptions on the Sun
Guest Editors: Jie Chen, Yuandeng Shen, Marianna Korsos, Robertus ErdelyiDeadline: 30 June 2024
Special Issue in
Universe
Advanced Studies in Ultra-High-Energy Cosmic Rays
Guest Editors: Gina Isar, François MontanetDeadline: 30 July 2024
Special Issue in
Universe
A Multimessenger View of Supermassive Black Holes and the Quasar Main Sequence
Guest Editors: Ascension Del Olmo, Paola MarzianiDeadline: 31 August 2024
Special Issue in
Universe
Particle Physics and Cosmology: A Themed Issue in Honor of Professor Dimitri Nanopoulos
Guest Editors: Jun-Jie Cao, Yungui Gong, Tianjun Li, Natsumi NagataDeadline: 1 September 2024
Topical Collections
Topical Collection in
Universe
New Results on Galaxy Evolution from the James Webb Space Telescope
Collection Editor: Guinevere Kauffmann
Topical Collection in
Universe
Modified Theories of Gravity and Cosmological Applications
Collection Editors: Panayiotis Stavrinos, Emmanuel N. Saridakis
Topical Collection in
Universe
Open Questions in Black Hole Physics
Collection Editors: Gonzalo Olmo, Diego Rubiera-Garcia
Topical Collection in
Universe
Nobel Prize 2020: Selected Articles on Black Hole and General Relativity
Collection Editor: Lorenzo Iorio