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Positron Annihilation Lifetime Spectroscopy (PALS) is sensitive to the material voids/free volume on the atomic scale. For this reason, this method has been used as a unique technology to measure the free volume and structural defects in polymers in recent years. In the present study, epoxy-matrix nanocomposites with different carboxylic acid functionalized multiwalled carbon nanotubes (COOH-MWCNTs) loadings (0.1-0.7 wt% at a step of 0.2) were fabricated, and the influence of COOH-MWCNTs loading on the prepared nanocomposites' free volume properties and tensile behavior were explored. The measurement of positron annihilation lifetime was done using a conventional synchronization system based on a 22Na radioactive source with 7 μCi activity. The detectors used in this work were fast plastic scintillators (type: NT-850) with ns time response. The results demonstrated that the tensile strength of the nanocomposites decreased with the increase in the lifetime of the ortho-positronium annihilation (increase in the radius and free volume) in the samples. The 0.3 wt% COOH-MWCNTs/epoxy nanocomposite showed the maximum tensile strength. Overall, the results of this work clearly revealed that there was a strong relationship between the tensile strength and free volume in the polymer nanocomposites.

The possibility of releasing unburned hydrocarbons and other compounds resulting from incomplete combustion from the exhaust is considered a common industrial issue. Pathing the exhaust gas through catalysts is a common way to lower the emissions. Alternatively, catalytic flameless combustion, used in a wide range of dilute air-fuel mixtures due to its optimal performance, is of interest for local radiative heating applications because of its low emission and high combustion efficiency (over 90%). However, using platinum catalysts in these systems increases production costs, and its surface temperature, ranging from 400-600 °C, faces a temperature limit in some applications. In this study, the feasibility of using a Pd-Au catalyst, with lower temperature and production costs, in a flameless catalytic counter-diffusive system was experimentally evaluated for the first time to reduce pollutants. A methane conversion rate of 98.3% in the 200-250 °C temperature range and a long life without CO and NOx pollutants were observed. This not only leads to reducing environmental pollutants, but by producing low-temperature radiant heat, it also provides the possibility of producing heat from exhaust gases, making it a dual-function solution in the field.

Acoustic levitation is the only method capable of suspending samples with different material properties and geometries, even in the liquid phase. Despite its widespread applications, droplet levitation still has a problem controlling the droplet’s position due to initial oscillations before reaching stability. This research investigates the effects of droplet physical properties, such as viscosity, radius, and density, on droplet oscillation amplitude. For this purpose, numerical simulations that apply the effect of the mentioned properties with acceptable accuracy and precision results were conducted using COMSOL Multiphysics 6.1 commercial software. The unique feature of using a simulation is the ability to study the effect of each parameter independently from the rest of the properties, which is not directly possible in experimental tests. The results emphasize the direct influence of viscosity on droplet oscillation amplitude. They also demonstrated that elevated viscosity leads to a decrease in droplet oscillation amplitude. In addition, increasing the density because of the added weight decreases the droplet amplitude. The droplet radius effect is more complicated because it is associated with two opposite effects. Increased droplet radius has the same effect as viscosity because of weight addition. On the other hand, a larger droplet's radius enlarges the cross-section and leads to a weak increase in droplet amplitude.

Obubra’s local government, located in the Cross River State of Nigeria, possesses commercial quantities of barite ores. These ore possess various forms of processing challenges. This paper presents research carried out to evaluate the efficacy of desliming to improve the physical properties of Obubra barite ore for its applications in the oil and gas industries. The desliming was carried out via elutriation using a floccumatic machine. The desliming parameters used in the experimental design were selected based on related literature; the factors and levels used included flowrates of 25.2 and 42.50 ml.s-1 and agitation times of 20 and 30 min. The physical and chemical responses were evaluated after each operation to evaluate the efficacy of each processing step. The optimal specific gravity after desliming was 4.18 g.cm-3, up from the raw value of 4.14 g.cm-3; the fineness or grain size remained the same at 75 µm; the moisture content was within the values of 0.01-0.02 % before and after the desliming process; while the pH value decreased to 7.06, from the raw value of 7.3. These results showed that Obubra barite ore can be upgraded by elutriation to meet the required American Petroleum Industry (API) specifications for use in the formulation of drilling mud.

Presented here is a bibliographic survey, which covers the work done in the period ranging from 1912 to 2023 on the various techniques employed in the processing of barite, along with the results obtained. This paper, the outcome of thorough research on various literature available from earlier studies, serves as a compendium of the major areas summarised in one paper. However, the objective of this paper was not to critique or review the outcomes of the various researchers. This article, which is essentially a one-stop guide handbook, will introduce the processing techniques used in barite processing, report the various research carried out by previous researchers using globally accepted processing techniques, and state the critical findings during the period under review.

Nematophagous fungi are widely utilized for biological control against both helminths and their intermediate hosts. This study investigates the fungus Monacrosporium thaumasium's potential in synthesizing silver nanoparticles (AgNPs). The efficacy of a crude extract from an M. thaumasium isolate (strain NF34) combined with silver nitrate (AgNO3) was tested on egg masses of Biomphalaria glabrata, serving as a model for embryotoxicity. The experiment followed a completely randomized design, with treatments containing AgNPs (in various proportions) and a control group with dechlorinated water maintained at 25 °C for ten days. Results indicate that M. thaumasium effectively produces AgNPs, causing 100% inhibition in exposed snail egg masses. The experimental results indicate that the fungus exhibits a potential molecular mechanism for nanoparticle formation, along with demonstrating embryotoxic activity in snail egg masses. These findings underscore the importance of further investigating this action and the underlying mechanism to provide potential applications in biological control.

We employ the simba-c cosmological simulation to study the impact of its upgraded chemical enrichment model (Chem5) on the distribution of metals in the intragroup medium (IGrM). We investigate the projected X-ray emission-weighted abundance profiles of key elements over two decades in halo mass (1013≤M500/M⊙≤1015). Typically, simba-c generates lower-amplitude abundance profiles than simba with flatter cores, in better agreement with observations. For low-mass groups, both simulations over-enrich the IGrM with Si, S, Ca, and Fe compared to observations, a trend likely related to inadequate modeling of metal dispersal and mixing. We analyze the 3D mass-weighted abundance profiles, concluding that the lower simba-c IGrM abundances are primarily a consequence of fewer metals in the IGrM, driven by reduced metal yields in Chem5, and the removal of the instantaneous recycling of metals approximation employed by simba. Additionally, an increased IGrM mass in low-mass simba-c groups is likely triggered by changes to the AGN and stellar feedback models. Our study suggests that a more realistic chemical enrichment model broadly improves agreement with observations, but physically motivated sub-grid models for other key processes, like AGN and stellar feedback and turbulent diffusion, are required to realistically reproduce observed group environments.

Alternative scenarios where the Big Bang singularity of the standard cosmological model is replaced by a bounce, or by an early almost static phase (known as emergent universe) have been frequently studied. We investigate the role of the spinor degrees of freedom in overcoming the initial singularity. We introduce a model which generalizes the Einstein–Cartan–Dirac theory, including local phase invariance of the spinor field supported by a gauge scalar field and certain couplings to the torsion. A natural gauge choice reduces the field equations to that of the Einstein–Dirac theory with a Dirac field potential that has polar and axial spinor currents. We identify a new potential term proportional to the square of the ratio of Dirac scalar and axial scalar, which provides a dark energy contribution dominating in the late-time Universe. In addition, the presence of spinor currents in the potential may induce the bounce of a contracting universe.

Recent studies have focused on how spinning black holes (BHs) within a binary system containing a strongly magnetized neutron star, then immersed in external magnetic fields, can acquire charge through mechanisms like the Wald process and how this charge could power pulsar-like electromagnetic radiation. Those objects called “Black hole pulsar” mimic the behaviour of a traditional pulsar, and they can generate electromagnetic fields, such as magnetic dipoles. Charged particles within an accretion disk around the black hole would then be influenced not only by the gravitational forces but also by electromagnetic forces, leading to different geometries and dynamics. In this context, we focus here on the interplay of the magnetic dipole and the accretion disk. We construct the equilibrium structures of non-conducting charged perfect fluids orbiting Kerr black holes under the influence of a dipole magnetic field aligned with the rotation axis of the BH. The dynamics of the accretion disk in such a system are shaped by a complex interplay between the non-uniform, non-Keplerian angular momentum distribution, the black hole’s induced magnetic dipole, and the fluid’s charge. We show how these factors jointly influence key properties of the disk, such as its geometry, aspect ratio, size, and rest mass density.

Dark matter, one of the fundamental components of the universe, has remained mysterious in modern cosmology and particle physics, and hence, this field is of utmost importance at the present moment. One of the foundational questions in this direction is the origin of dark matter, which directly links to its creation. In the present article, we study the gravitational production of dark matter in two distinct contexts: firstly, when reheating occurs through gravitational particle production, and secondly, when it is driven by decay of the inflaton field. We establish a connection between the reheating temperature and the mass of dark matter, and from the reheating bounds, we determine the range of viable dark matter mass values.

The positions of millisecond pulsars (MSPs) can be determined with sub-milliarcsecond (mas) accuracy using both Very Long Baseline Interferometry (VLBI) and timing, referenced to the International Celestial Reference Frame (ICRF) and planetary ephemerides frame, respectively, representing kinematic and dynamical reference frames. The two frames can be connected through observations of common celestial objects, MSPs observed with VLBI and timing. However, previous attempts to establish this connection were unreliable due to the limited number of MSPs observed by both techniques. Currently, 23 MSPs have been precisely measured using both multiple timing and VLBI networks. Among them, 17 MSPs are used to link the two reference frames, marking a significant three-fold increase in the number of common MSPs used for frame linking. Nevertheless, six MSPs located near the ecliptic plane are excluded from frame linkage due to positional differences exceeding 20 mas measured by VLBI and timing. This discrepancy is primarily attributed to errors introduced in fitting positions in timing methods. With astrometric parameters obtained via both VLBI and timing for these MSPs, the precision of linking DE436 and ICRF3 has surpassed 0.4 mas. Furthermore, thanks to the improved timing precision of MeerKAT, even with data from just 13 MSPs observed by both MeerKAT and VLBI, the precision of linking DE440 and ICRF3 can also exceed 0.4 mas. The reliability of this linkage depends on the precision of pulsar astrometric parameters, their spatial distribution, and discrepancies in pulsar positions obtained by the two techniques. Notably, proper motion differences identified by the two techniques are the most critical factors influencing the reference frame linking parameters. The core shift of the calibrators in VLBI pulsar observations is one of the factors causing proper motion discrepancies, and multi-wavelength observations are expected to solve it. With the improvement in timing accuracy and the application of new observation modes like multi-view and multi-band observations in VLBI, the linkage accuracy of the dynamical and kinematic reference frames is expected to reach 0.3 mas.

In this article, we consider the 4 + n dimensional spacetimes among which one is the four dimensional physical Universe and the other is an n-dimensional sphere with constant radius in the framework of Lanczos-Lovelock gravity. We find that the curvature of extra dimensional sphere contributes a huge but negative energy density provided that its radius is sufficiently small, such as the scale of Planck length. Therefore, the huge positive vacuum energy, i.e., the large positive cosmological constant is exactly cancelled out by the curvature of extra sphere. In the mean time the higher order of Lanczos-Lovelock term contributes an observations-allowed small cosmological constant if the number of extra dimensions is sufficiently large, such as n ≈ 69.

In our previous work, we investigated the spectra and anisotropy of galactic cosmic rays (GCRs) under the assumption of an axisymmetric distribution of galactic sources. Currently, much observational evidence indicates that the Milky Way is a typical spiral galaxy. In this work, we further utilize an anisotropic propagation model under the framework of spiral distribution sources to study spectra and anisotropy. During the calculation process, we adopt the spatial-dependent propagation (SDP) model, while incorporating the contribution from the nearby Geminga source and the anisotropic diffusion of cosmic rays (CRs) induced by the local regular magnetic field (LRMF). By comparing the results of background sources with spiral and axisymmetric distribution models, it is found that both of them can well reproduce the CR spectra and anisotropy. However, there exist differences in their propagation parameters. The diffusion coefficient with spiral distribution is larger than that with axisymmetric distribution, and its spectral indices are slightly harder. To investigate the effects of a nearby Geminga source and LRMF on anisotropy, two-dimensional (2D) anisotropy sky maps under various contributing factors are compared. Below 100 TeV, the anisotropy is predominantly influenced by both the nearby Geminga source and the LRMF, causing the phase to align with the direction of the LRMF. Above 100 TeV, the background sources become dominant, resulting in the phase pointing towards the Galactic Center (GC). Future high-precision measurements of CR anisotropy and spectra, such as the LHAASO experiment, will be crucial in evaluating the validity of our proposed model.

About twelve years ago, the use of standard functional manipulations was demonstrated to imply an unexpected property satisfied by the fermionic Green’s functions of QCD. This non-perturbative phenomenon has been dubbed an effective locality. In a much simpler way than in QCD, the most remarkable and intriguing aspects of effective locality have been presented in a recent publication on the Yang-Mills theory on Minkowski spacetime. While quickly recalled in the current paper, these results are used to calculate the problematic gluonic propagator in the Yang-Mills non-perturbative regime. This paper is dedicated to the memory of Professor Herbert M. Fried (1929–2023), whose inspiring manner, impressive command of functional methods in quantum field theories, enthusiasm for a broad range of topics in Theoretical Physics, and warm friendship are missed greatly by the authors.

While fluvial features are plentiful on Mars and offer valuable insights into past surface conditions, the climatic conditions inferred from these valleys, like precipitation and surface runoff discharges, remain the subject of debate. Model-based estimations have already been applied to several Martian valleys, but exploration of the related numerical estimations has been limited. This work applies an improved precipitation-based, steady-state erosion/accumulation model to a Martian valley and compares it to a terrestrial Mars analogue dessert catchment area. The simulations are based on a previously observed precipitation event and estimate the fluvial-related hydrological parameters, like flow depth, velocity, and erosion/accumulation processes in two different but morphologically similar watersheds. Moderate differences were observed in the erosion/accumulation results (0.13/−0.06 kg/m2/s for Zafit (Earth) and 0.01/−0.007 for Tinto B (Mars)). The difference is probably related to the lower areal ratio of surface on Mars where the shield factor is enough to trigger sediment movement, while in the Zafit basin, there is a larger area of undulating surface. The model could be applied to the whole surface of Mars. Using grain size estimation from the global THEMIS dataset, the grain size value artificially increased above that observed, and decreased hypothetic target rock density tests demonstrated that the model works according to theoretical expectations and is useful for further development. The findings of this work indicate the necessity of further testing of similar models on Mars and a better general analysis of the background geomorphological understanding of surface evolution regarding slope angles.

In this article, we continue our investigation on how the electromagnetic waves propagate in the Friedman–Lemaître–Robertson–Walker spacetime. Unlike the standard approach, which relies on null geodesics and geometric optics approximation, we derive explicit solutions for electromagnetic waves in expanding spacetime and examine their implications for cosmological observations. In particular, our analysis reveals potential modifications to the standard luminosity distance formula. Its effect on other cosmological parameters, e.g., the amount of cold dust matter in the Universe, is considered and estimated from Type Ia supernovae data. We see that this alternative model is able to fit the supernova data, but it gives a qualitatively different Universe without a cosmological constant but with stiff or ultra-stiff matter.

Scan Quantum Mechanics (SQM) is a novel interpretation in which the superposition of states is only an approximate effective concept due to lack of time resolution. Quantum systems scan all possible states in the “apparent” superpositions and switch randomly and very rapidly among them. A crucial property that we postulate is quantum inertia Iq, that increases whenever a constituent is added, or the system is perturbed with all kinds of interactions. Once the quantum inertia reaches a critical value Icr for an observable, the switching among its eigenvalues stops and the corresponding superposition comes to an end. Consequently, increasing the quantum inertia of a quantum system by increasing its mass, its temperature, or the strength of the electric, magnetic and gravitational fields in its environment, can lead to the end of the superpositions for all the observables, the quantum system transmuting into a classical one, as a result. This process could be reversible, however, by decreasing the size of the system, its temperature, etc. SQM also implies a radiation mechanism from astrophysical objects with very strong gravitational fields that could contribute to neutron star formation. Future experiments might determine the critical quantum inertia Icr corresponding to different observables, which translates into critical masses, critical temperatures and critical electric, magnetic and gravitational fields.

We explore the evolutionary link between Galactic Be X-ray binaries (BeXBs) and Galactic field double neutron stars (DNSs) based on the properties of the NS spin period—P and binary orbital period—Porb. First, both BeXB and DNS sources show positive correlation trends in P versus Porb relation (P−Porb diagram), which may relate to the influence of the accretion evolution. Secondly, the two types of sources exhibit similar bi-modal P/Porb distributions with the gaps of P∼40 s/Porb∼60 days for BeXBs and P∼50 ms/Porb∼1 day for DNSs, respectively. We propose a possibility that Galactic BeXBs may transfer the bi-modal P/Porb classifications to Galactic field DNSs during the evolution process. Furthermore, based on the bi-modal gaps, we infer the contraction factors of P (by ∼1800) and Porb (by ∼160) valuesin the evolution from Galactic BeXBs to Galactic field DNSs. We find that the scaled P or Porb values of Galactic BeXBs share the similar bi-modal distributions to that of Galactic field DNSs, and these results can offer a reference to trace the classification and evolution between the two types of sources.

This is the Part III paper of our series of papers on a gauge-invariant perturbation theory on the Schwarzschild background spacetime. After reviewing our general framework for the gauge-invariant perturbation theory and the proposal for gauge-invariant treatments of l=0,1 mode perturbations on the Schwarzschild background spacetime in the Part I paper, we examine the problem of whether the l=0,1 even-mode solutions derived in the Part II paper are physically reasonable. We consider the linearized versions of the Lemaître–Tolman–Bondi solution and the non-rotating C-metric. As a result, we show that our derived even-mode solutions to the linearized Einstein equations realize these two linearized solutions. This supports the conclusion that our derived solutions are physically reasonable, which implies that our proposal for gauge-invariant treatments of l=0,1 mode perturbations is also physically reasonable. We also briefly summarize the conclusions of our series of papers.

The enigmatic phenomenon of dark energy (DE) is the elusive entity driving the accelerated expansion of our Universe. A plausible candidate for DE is the non-zero Einstein Cosmological Constant ΛE manifested as a constant energy density of the vacuum, yet it seemingly defies gravitational effects. In this work, we interpret the non-zero ΛE through the lens of scale-invariant cosmology. We revisit the conformal scale factor λ and its defining equations within the Scale-Invariant Vacuum (SIV) paradigm. Furthermore, we address the profound problem of the missing mass across galactic and extragalactic scales by deriving an MOND-like relation, g∼a0gN, within the SIV context. Remarkably, the values obtained for ΛE and the MOND fundamental acceleration, a0, align with observed magnitudes, specifically, a0≈10−10ms−2 and ΛE≈1.8×10−52m−2. Moreover, we propose a novel early dark energy term, T˜μν∼κH, within the SIV paradigm, which holds potential relevance for addressing the Hubble tension.

We analyze the anisotropic Bianchi models, and in particular the Bianchi Type IX known as the Mixmaster universe, where the Misner anisotropic variables obey Deformed Commutation Relations inspired by Quantum Gravity theories. We consider three different deformations, two of which have been able to remove the initial singularity similarly to Loop Quantum Cosmology when implemented in the single-volume variable. Here, the two-dimensional algebras naturally implement a form of Non-Commutativity between the space variables that affects the dynamics of the anisotropies. In particular, we implement the modifications in their classical limit, where the Deformed Commutators become Deformed Poisson Brackets. We derive the modified Belinskii–Khalatnikov–Lifshitz map in all the three cases, and we study the fate of the chaotic behavior that the model classically presents. Depending on the sign of the deformation, the dynamics will either settle into oscillations between two almost-constant angles, or stop reflecting after a finite number of iterations and reach the singularity as one last simple Kasner solution. In either case, chaos is removed.

Two-flavor neutrino oscillation is analyzed using the consistent histories approach. We identify the properties of neutrinos and the oscillation conditions, such as the presence of matter or the impact of measurement, that ensure the consistency of three-time neutrino histories. The connection between the consistency of these histories and the well-known CP violation explored in this study serves as a specific example.

In the present work, we study cosmology in dilatonic f(R,T) gravity to address the inflationary phase of the early universe. As usual, in dilatonic gravity, the scalar potential assumes the exponential form. However, this potential is not good enough to be in accordance with the Planck 2018 data. More strikingly, the generalized β-exponential cannot take this into account either. It is just only presence of the dilatonic sector, in the intermediate coupling regime, that can help the theory to be in full accordance with the observational data.

Based on Newtonian mechanics, in this article, we present a heuristic derivation of the Friedmann equations, providing an intuitive foundation for these fundamental relations in cosmology. Additionally, using the first law of thermodynamics and Euler’s equation, we derive a set of equations that, at linear order, coincide with those obtained from the conservation of the stress-energy tensor in general relativity. This approach not only highlights the consistency between Newtonian and relativistic frameworks in certain limits, but also serves as a pedagogical bridge, offering insights into the physical principles underlying the dynamics of the universe.

We study the dynamics of a coherent state of closed type II string gravitons within the framework of the Steepest Entropy Ascent Quantum Thermodynamics, an effective model where the quantum evolution is driven by a maximal increase of entropy. We find that by perturbing the pure coherent state of gravitons by the presence of other states in the string spectrum, there exist conditions upon which the system undergoes decoherence by reaching thermodynamical equilibrium. This suggests the instability of the coherent state of gravitons. We identify the time scale it takes the system to reach equilibrium consisting of a mixed state of fields in the string spectrum and compare it with the quantum-break time. Also we find that in such final state the quantum-break time seems to be larger than the classical break-time.

The first part of this work provides a review of recent research on generalised entropies and their origin, as well as its application to black hole thermodynamics. To start, it is shown that the Hawking temperature and the Bekenstein–Hawking entropy are, respectively, the only possible thermodynamical temperature and entropy of the Schwarzschild black hole. Moreover, it is investigated if the other known generalised entropies, which include Rényi’s entropy, Tsallis entropy, and the four- and five-parameter generalised entropies, could correctly yield the Hawking temperature and the ADM mass. The possibility that generalised entropies could describe hairy black hole thermodynamics is also considered, both for the Reissner–Nordström black hole and for Einstein’s gravity coupled with two scalar fields. Two possibilities are investigated, namely, the case when the ADM mass does not yield the Bekenstein–Hawking entropy, and the case in which the effective mass expressing the energy inside the horizon does not yield the Hawking temperature. For the model with two scalar fields, the radii of the photon sphere and of the black hole shadow are calculated, which gives constraints on the BH parameters. These constraints are seen to be consistent, provided that the black hole is of the Schwarzschild type. Subsequently, the origin of the generalised entropies is investigated, by using their microscopic particle descriptions in the frameworks of a microcanonical ensemble and canonical ensemble, respectively. Finally, the McLaughlin expansion for the generalised entropies is used to derive, in each case, the microscopic interpretation of the generalised entropies, via the canonical and the grand canonical ensembles.

Thermal relics with masses in the GeV to TeV range remain possible candidates for the Universe’s dark matter (DM). These neutral particles are often assumed to have vanishing electric and magnetic dipole moments so that they do not interact with single real photons, but the anapole moment, a static electromagnetic property whose features are akin to that of a classical toroidal solenoid, can still be non-zero, permitting interactions with single virtual photons. In some models, DM predominantly annihilates into charged standard model particles through a p-wave process mediated by the anapole moment. The anapole moment is also responsible for another interaction of interest. If a DM medium were subjected to an electric current, a DM particle whose anapole moment was aligned with the current would have lower energy than the state with an antialigned anapole moment. Given these interactions, if a collection of initially unpolarized DM particles were subjected to an electric current, then the DM medium would become partially polarized, according to the Boltzmann distribution. In such a polarized medium, DM annihilation into photons, a subdominant s-wave process realizable through higher order interactions, would be somewhat suppressed. If the local electric current existed during a time in which the DM begins to drop out of thermal equilibrium with the rest of the Universe, the suppressed annihilation could lead to a small local excess in the relic DM density relative to a current-free region. This mechanism by which the local DM density can be perturbed is novel. Using effective interactions to model a DM particle’s anapole moment and polarizabilities (responsible for s-wave annihilation into two photons), we compute the changes in the DM density produced by long- and short-lived currents around freeze out. If we employ the most stringent constraints on DM annihilation into two photons, we find that long-lived currents can result in a fractional change in the DM density on the order of 10−17 for DM masses around 100 GeV; for short-lived currents, this fractional change in local DM density is on the order of 10−23 for the same DM mass.

Be stars are rapidly rotating B-type stars surrounded by circumstellar disks formed from self-ejected material. Understanding the mechanisms driving mass ejection and disk formation, known as the Be phenomenon, requires a detailed investigation of their variability and underlying physical processes. In this study, we analyze the photometric, spectroscopic, and seismic characteristics of three Be stars—HD 212044, 28 Cyg, and HD 174237—using high-cadence data from the TESS mission and spectral data from the BeSS database. Photometric variability was analyzed through iterative prewhitening and wavelet techniques, revealing distinct frequency groups associated with non-radial pulsations (NRPs). Spectral data provided equivalent width measurements of the Hα line, which correlated with photometric changes, reflecting dynamic interactions between the stars and their disks. Seismic analysis identified core rotation rates and buoyancy travel times for HD 212044 and 28 Cyg, offering insights into internal stellar processes and angular momentum distribution. HD 212044 exhibits a strong negative correlation between photometric brightness and Hα equivalent width, whereas this correlation is weaker in the case of 28 Cyg. The findings for these two stars highlight the interplay between NRPs, rapid rotation, and circumstellar disk dynamics. In contrast, the case of HD 174237 presents an example of how a binary system with mass transfer and a B-type component is revealed when observed simultaneously with space-based photometry and ground-based spectroscopy, demonstrating the importance of distinguishing classical Be stars from interacting binaries.

On 25 February 2014 at around 00:39 UT, a major solar flare (code: SOL2014-02-25T00:39) erupted at sunspot region AR11990. Using the updated science quality data of GOES-15, it has been classified as an X7.13 solar flare. This gave rise to the electron density changes that affected the strengths of ionospheric electric currents. In this work, the difference in total electron content (TEC), between the TEC during a flare day and a quiet, fitted TEC, ΔTEC, and rate of change of TEC, dTEC/dt, are determined to observe electron density changes due to the solar flare over a low-latitude region. These stations are at Quezon City (PIMO) and Taguig City (PTAG). Also, responses in the geomagnetic field component, ΔH, are calculated along with the variations in the equatorial electrojet (EEJ) strength. These are observed at equatorial, Davao (DAV) and Cagayan de Oro (CDO), and off-equatorial, Muntinlupa (MUT) and Legazpi (LGZ), stations. The resulting ΔTEC values were 1.17–1.97 TECU while dTEC/dt maxima were 0.29–0.48 TECU/min. The dTEC/dt maxima were found to concur with the time the solar EUV reached peak intensity at 00:45 UT, 4 min before the flare (i.e., X-ray) peaked. Furthermore, the ΔH variations exhibited larger enhancements at the equatorial stations. These are mostly attributed to the EEJ contributing to the geomagnetic field variations. The amplification experienced by the EEJ due to the increased ionospheric conductivity is then reflected in the geomagnetic responses. For the CDO-LGZ stations, the EEJ strength reached ~37 nT, while for the DAV-MUT, this was ~60 nT.

This review provides an observational perspective on the fundamental properties of super-Eddington accretion onto supermassive black holes in quasars. It begins by outlining the selection criteria, particularly focusing on optical and UV broad-line intensity ratios, used to identify a population of unobscured super-Eddington candidates. Several defining features place these candidates at the extreme end of the Population A in main sequence of quasars: among them are the highest observed singly-ionized iron emission, extreme outflow velocities in UV resonance lines, and unusually high metal abundances. These key properties reflect the coexistence of a virialized sub-system within the broad-line region alongside powerful outflows, with the observed gas enrichment likely driven by nuclear or circumnuclear star formation. The most compelling evidence for the occurrence of super-Eddington accretion onto supermassive black holes comes from recent observations of massive black holes at early cosmic epochs. These black holes require rapid growth rates that are only achievable through radiatively inefficient super-Eddington accretion. Furthermore, extreme Eddington ratios, close to or slightly exceeding unity, are consistent with the saturation of radiative output per unit mass predicted by accretion disk theory for super-Eddington accretion rates. The extreme properties of super-Eddington candidates suggest that these quasars could make them stable and well-defined cosmological distance indicators, leveraging the correlation between broad-line width and luminosity expected in virialized systems. Finally, several analogies with accretion processes around stellar-mass black holes, particularly in the high/soft state, are explored to provide additional insight into the mechanisms driving super-Eddington accretion.

Addressing the astronomical challenges posed by the interplay of data volume, AI sophistication, and energy consumption is crucial for the future of astronomy. As astronomical surveys continue to produce vast amounts of data, the computational and energy demands for galaxy classification have escalated, necessitating more efficient and sustainable approaches. This study presents a novel application of tensor factorization within the Faster R-CNN framework, resulting in the development of our model, T-Faster R-CNN, designed to enhance both the energy efficiency and computational performance of deep learning models used in galaxy classification. By integrating tensor factorization, our T-Faster R-CNN significantly reduces the model’s complexity, memory footprint, and CO2 emissions, while maintaining, and in some cases even improving, the accuracy of morphological classification. The effectiveness of this optimized model is validated using data from the Galaxy Zoo DECaLS, where it demonstrates substantial improvements in computational efficiency without compromising classification precision. Furthermore, this research incorporates green code principles, emphasizing reductions in energy consumption and environmental impact in computational astronomy. The T-Faster R-CNN model offers a resource-efficient, sustainable methodology for analyzing large-scale astronomical data, addressing the critical need for greener computational practices in the era of big data.

It is always more evident that the kinematics of galaxies provide us with unique information on the Nature of the dark particles and on the properties of the galaxy Dark Matter (DM) halos. However, in investigating this topic, we have to be very careful about certain issues related to the assumptions that we take or to the practices that we follow. Here, we critically discuss such issues, that, today, result of fundamental importance, in that we have realized that the Nature of the DM will be not provided by “The Theory” but, has to be inferred by reverse engineering the observational scenario.

We investigate the impact of dark fluid accretion on gravitational waveforms emitted by a compact binary system consisting of a supermassive black hole and a stellar-mass black hole. Using a Lagrangian framework with 1 PN and 2.5 PN corrections, we analyze the effects of the spherically symmetric accretion of a fluid with steady-state flow, including those characterized by an equation of state parameter resembling dark energy, on the binary’s dynamics. We validate our approach by comparing it with previous studies in the common region of validity and extend the analysis to include both local effects, such as dynamical friction, and global gravitational interactions with the stellar-mass black hole, focusing on their dependence on the fluid’s properties. Our analysis reveals that these interactions induce de-phasing in gravitational waveforms, with the phase shift influenced by the fluid’s equation of state and energy density. We also extend the study to sudden cosmological singularities, finding that, although they can deform the binary’s orbit from initially circular to elliptical, their effect on de-phasing is negligible for cosmologically relevant energy densities. By incorporating both the local and global gravitational interactions of a fluid on a two-body system into the equations of motion, this preliminary study provides a framework for understanding the interplay between fluid dynamics and gravitational wave emissions in astrophysical systems. It further reinforces the potential for probing the properties of astrophysically relevant fluids through gravitational wave observations.

We present a comprehensive comparison of different Markov chain Monte Carlo (MCMC) sampling methods, evaluating their performance on both standard test problems and cosmological parameter estimation. Our analysis includes traditional Metropolis–Hastings MCMC, Hamiltonian Monte Carlo (HMC), slice sampling, nested sampling as implemented in dynesty, and PolyChord. We examine samplers through multiple metrics including runtime, memory usage, effective sample size, and parameter accuracy, testing their scaling with dimension and response to different probability distributions. While all samplers perform well with simple Gaussian distributions, we find that HMC and nested sampling show advantages for more complex distributions typical of cosmological problems. Traditional MCMC and slice sampling become less efficient in higher dimensions, while nested methods maintain accuracy but at higher computational cost. In cosmological applications using BAO data, we observe similar patterns, with particular challenges arising from parameter degeneracies and poorly constrained parameters.

We study the Stueckelberg field in de Sitter space, which is a massive vector field with the gauge fixing (GF) term 12ζ(Aμ;μ)2. We obtain the vacuum stress tensor, which consists of the transverse, longitudinal, temporal, and GF parts, and each contains various UV divergences. By the minimal subtraction rule, we regularize each part of the stress tensor to its pertinent adiabatic order. The transverse stress tensor is regularized to the 0th adiabatic order, while the longitudinal, temporal, and GF stress tensors are regularized to the 2nd adiabatic order. The resulting total regularized vacuum stress tensor is convergent and maximally symmetric, has a positive energy density, and respects the covariant conservation, and thus, it can be identified as the cosmological constant that drives the de Sitter inflation. Under the Lorenz condition Aμ;μ=0, the regularized Stueckelberg stress tensor reduces to the regularized Proca stress tensor that contains only the transverse and longitudinal modes. In the massless limit, the regularized Stueckelberg stress tensor becomes zero, and is the same as that of the Maxwell field with the GF term, and no trace anomaly exists. If the order of adiabatic regularization were lower than our prescription, some divergences would remain. If the order were higher, say, under the conventional 4th-order regularization, more terms than necessary would be subtracted off, leading to an unphysical negative energy density and the trace anomaly simultaneously.

In this paper, we conduct a thorough investigation of the surface and curvature tensions, σ and γ, of three-flavor cold quark matter using the Nambu–Jona–Lasinio (NJL) model with vector interactions. Our approach ensures both local and global electric charge neutrality, as well as chemical equilibrium under weak interactions. By employing the multiple reflection expansion formalism to account for finite size effects, we explore the impact of specific input parameters, particularly the vector coupling constant ratio ηV, the radius R of quark matter droplets, as well as the charge-per-baryon ratio ξ of the finite size configurations. We focus on the role of the contributions of each term of the NJL Lagrangian to the surface and curvature tensions in the mean field approximation. We find that the total surface tension exhibits two different density regimes: it remains roughly constant at around 100MeVfm−2 up to approximately 2–4 times the nuclear saturation density, and beyond this point, it becomes a steeply increasing function of nB. The total surface and curvature tensions are relatively insensitive to variations in R but are affected by changes in ξ and ηV. We observe that the largest contribution to σ and γ comes from the regularized divergent term, making these quantities significantly higher than those obtained within the MIT bag model.

According to general relativity, the cosmological redshift may be caused by other mechanisms than the source moving away from the observer. It can occur on a global scale, similar to the gravitational redshift near massive stars. In principle, these are differences in the time-dependent global metric field between the source in the past and the observer in the present. In this paper we attempt a new interpretation of the simple solution of Einstein’s equations within a fully conformal metric for the case of a time-independent energy-momentum tensor. The scaling factor here acts identically on all four space-time coordinates and the speed of light is independent of the conformal time. The fully conformal metric is interpreted here as a universal geometric background which is scale invariant and acts universally on all objects, including gauges and clocks, regardless of their dimensions and internal interactions. The associated scale invariant exponential expansion is thus only relative and all observers at different times are completely equal. The model introduces the concept of the appearent age of the universe, which is the limiting consequence of time dilation into the past, and corresponds to the present value of the age of the universe H−1 according to the standard model. This appearent age is the same for all observers, and the Hubble constant is thus a true universal constant, invariant to time translations. The motivation of this work was to test the possibility of the above cosmological redshift mechanism in confrontation with astrophysical data. Probably the most important consequence is the generalized formulation and interpretation of the Hubble-Lemaître law z(r) = (eHr/c − 1), which shows good agreement with astrophysical data even for the most distant supernovae. Confronting the conformal metric model with some astrophysical data shows an interesting agreement with the observed spatial distribution of astrophysical sources such as γ-ray bursts and quasars. On a cosmological scale, the above fully conformal metric naturally determines the global energy density, spatial flatness, and solves the horizon problem and Olbers’ paradox in infinite spacetime.

The concentration of dark matter haloes is closely linked to their mass accretion history. We utilize the halo mass accretion histories from large cosmological N-body simulations as inputs for our neural networks, which we train to predict the concentration of individual haloes at a given redshift. The trained model performs effectively in other cosmological simulations, achieving the root mean square error between the actual and predicted concentrations that significantly lower than that of the model by Zhao et al. and Giocoli et al. at any redshift. This model serves as a valuable tool for rapidly predicting halo concentrations at specified redshifts in large cosmological simulations.

The relativistic jets of gamma-ray bursts (GRBs) might be powered by a black-hole (BH) hyperaccretion system. The inherent asymmetry in these jets generates recoil forces, inducing oscillations and positional deviations of the BH from equilibrium. In this study, we explore the influence of different initial BH mass, spin, and mass accretion rate, as well as their evolutions on the dynamical properties of BH under the effect of asymmetric jets. Our results reveal that the initial mass and accretion rate significantly impact the BH’s acceleration, velocity, and displacement, while the different initial spin plays a negligible role in shaping the overall dynamical evolution. Additionally, we calculate the gravitational wave (GW) strains associated with the asymmetric jets, finding that the resulting GW signals are too weak to be detected, even for nearby GRBs. These findings provide critical insights into the dynamical response of BHs to asymmetric jets and the associated GW radiation, advancing our understanding of BH physics in GRBs.

We fit the three finestructure constants of the Standard Model, in which the first approximation of theoretically estimable parameters include (1) a “unified scale”, turning out not equal to the Planck scale and thus only estimable by a very speculative story, the second includes (2) a “number of layers” being a priori the number of families, and the third is (3) a unified coupling related to a critical coupling on a lattice. So formally, we postdict the three fine structure constants! In the philosophy of our model, there is a physical lattice theory with link variables taking values in a (or in the various) “small” representation(s) of the standard model Group. We argue for that these representations function in the first approximation based on the theory of a genuine SU(5) theory. Next, we take into account fluctuation of the gauge fields in the lattice and obtain a correction to the a priori SU(5) approximation, because of course the link fluctuations not corresponding to any standard model Lie algebra, but only to the SU(5), do not exist. The model is a development of our old anti-grand-unification model having as its genuine gauge group, close to fundamental scale, a cross-product of the standard model group S(U(3)×U(2)) with itself, with there being one Cartesian product factor for each family. In our old works, we included the hypothesis of the “multiple point criticallity principle”, which here effectively means the coupling constants are critical on the lattice. Counted relative to the Higgs scale, we suggest in our sense that the“unified scale” (where the deviations between the inverse fine structure constants deviate by quantum fluctuations being only from standard model groups, not SU(5)) makes up the 2/3rd power of the Planck scale relative to the Higgs scale or the topquarkmass scale.

When radiation from a background source passes through a cloud of cold plasma, diverging lensing occurs if the source and observer are well-aligned. Unlike gravitational lensing, plasma lensing is dispersive, increasing in strength with wavelength. The Drude model is a generalization of cold plasma, including absorbing dielectric dust described by a complex index of refraction. The Drude lens is only dispersive for wavelengths shorter than the dust characteristic scale (λ≪λd). At sufficient photon energy, the dust particles act like refractive clouds. For longer wavelengths λ≫λd, the optical properties of the Drude lens are constant, unique behavior compared to the predictions of the cold plasma lens. Thus, cold plasma lenses can be distinguished from Drude lenses using multi-band observations. The Drude medium extends the applicability of all previous tools, from gravitational and plasma lensing, to describe scattering phenomena in the X-ray regime.

We apply extended local hidden-gauge formalism to study meson–meson interactions with the quark constituents ccc¯c¯, ccc¯b¯/c¯c¯cb, ccb¯b¯/c¯c¯bb, bbc¯b¯/b¯b¯cb, and bbb¯b¯, in which the exchanged mesons are the fully heavy vector mesons J/ψ, Bc* and Υ. We solve the coupled-channel Bethe–Salpeter equation to derive two poles in the bbc¯b¯ system and two poles in the ccc¯b¯ system. There are also four charge-conjugated poles in the b¯b¯cb and c¯c¯cb systems. In the bbc¯b¯ system, one pole corresponds to a sub-threshold bound state when the cutoff momentum is set to Λ>850 MeV. The other pole in this system corresponds to a sub-threshold bound state when Λ>1100 MeV. In the ccc¯b¯ system, the two poles correspond to sub-threshold bound states only when Λ>1550 MeV and Λ>2650 MeV. This makes them difficult to identify as deeply bound hadronic molecules. We propose investigating the two poles of the bbc¯b¯ system in the μ+μ−Bc− channel at the LHC.

Gamma-ray production by proton–proton (pp) inelastic collisions plays an important role in searching for cosmic-ray (CR) accelerators. Understanding the pionic gamma-ray production associated with giant molecular/atomic clouds is thus crucial to identify this process. In this work, we study the feedback of the pionic gamma-ray production to the CR distribution, by considering collision-induced energy loss on cosmic-ray protons in the dense core region of molecular clouds (MCs). We try to introduce a Monte Carlo simulation framework to quantify this effect, and present a detailed analysis to evaluate how pp collisions harden the cosmic-ray proton spectrum and the resulting gamma-ray spectrum in giant clouds.

In the present work, we investigate anisotropic compact stars under the general relativistic platform. Following a novel technique, we found an exact self-bound analytical stellar solution. The obtained solution was matched on the spherical surface of the boundary to the Schwarzschild metric in order to find the expressions of the constants involved in the neutral system. We conducted various critical investigations such as on the variations in pressures, density, energy conditions, pressure–density ratios, the velocity of sounds, and gravitational potentials within stellar objects. We also conducted a stability analysis of the models using the cracking concepts and the adiabatic index. The values of the constant parameters were taken corresponding to the secondary components of GW190814 to validate the physical viability of our solution. This study provides fruitful results that are physically viable and, hence, satisfactory.

This article is Part I of our series of full papers on a gauge-invariant “linear” perturbation theory on the Schwarzschild background spacetime which was briefly reported in our short papers by the present author in 2021. We first review our general framework of the gauge-invariant perturbation theory, which can be easily extended to the “higher-order” perturbation theory. When we apply this general framework to perturbations on the Schwarzschild background spacetime, gauge-invariant treatments of l=0,1 mode perturbations are required. On the other hand, in the current consensus on the perturbations of the Schwarzschild spacetime, gauge-invariant treatments for l=0,1 modes are difficult if we keep the reconstruction of the original metric perturbations in our mind. Due to this situation, we propose a strategy of a gauge-invariant treatment of l=0,1 mode perturbations through the decomposition of the metric perturbations by singular harmonic functions at once and the regularization of these singularities through the imposition of the boundary conditions to the Einstein equations. Following this proposal, we derive the linearized Einstein equations for any modes of l≥0 in a gauge-invariant manner. We discuss the solutions to the odd-mode perturbation equations in the linearized Einstein equations and show that these perturbations include the Kerr parameter perturbation in these odd-mode perturbations, which is physically reasonable. In the Part II and Part III papers of this series of papers, we will show that the even-mode solutions to the linearized Einstein equations obtained through our proposal are also physically reasonable. Then, we conclude that our proposal of a gauge-invariant treatment for l=0,1-mode perturbations is also physically reasonable.

In this paper, we describe the study of one- and three-dimension pion and kaon source functions for chaotic and partially coherent sources in Pb-Pb central collisions at sNN=2.76 TeV using the AMPT model. The characteristic source function quantities are calculated and compared with the results obtained by fitting the two-boson correlation functions using the Gaussian source formula. It was found that the imaging results are approximately consistent with the results of the Gaussian source formula fits. The partially coherent pion sources exhibit a high degree of coherence. However, the kaon pairs with high transverse momenta are emitted with a high degree of chaos.

In this study, we investigate the properties of a thin accretion disk around a static spherically symmetric black hole in 4D Einstein–Gauss–Bonnet gravity, with an additional coupling constant, α, appearing in the spacetime metric. Using the Novikov–Thorne accretion disk model, we examine the thermal properties of the disk, finding that increasing α reduces the energy, angular momentum, and effective potential of a test particle orbiting the black hole. We demonstrate that α can mimic the spin of a Kerr black hole in general relativity up to a≃ 0.23 M for the maximum value of α. Our analysis of the thermal radiation flux shows that larger α values increase the flux and shift its maximum towards the central black hole, while far from the black hole, the solution recovers the Schwarzschild limit. The impact of α on the radiative efficiency of the disk is weak but can slightly alter it. Assuming black-body radiation, we observe that the disk’s temperature peaks near its inner edge and is higher for larger α values. Lastly, the electromagnetic spectra reveal that the disk’s luminosity is lower in Einstein–Gauss–Bonnet gravity compared to general relativity, with the peak luminosity shifting toward higher frequencies, corresponding to the soft X-ray band as α increases.

We consider the Weyl invariant theory of gravity as an alternative approach to the problem of the origin of dark matter. According to this theory, the geometric Weyl 1-form effectively behaves as a Proca field. In this work, our starting point is to consider the existence of a gas of Weyl–Proca particles in a Bose–Einstein condensate and investigate its behavior in a cosmological context. The results obtained show that, for appropriate values of the free parameter of the model, the Weyl field behaves approximately as a dust fluid in the matter-dominated era as expected for a dark matter candidate.

The dispersion measures (DMs) of the fast radio bursts (FRBs) are a valuable tool to probe the baryonic content of the intergalactic medium and the circumgalactic medium of the intervening galaxies along the sightlines. However, interpreting the DMs is complicated by the contribution of the hot gas in and around our Milky Way. This study examines the relationship between DMMW, derived from localized FRBs, and the Galaxy’s hot gas, using X-ray absorption and emission data from O vii and O viii. We find evidence for a positive correlation between DMMW and O vii absorption, reflecting contributions from both the disk and halo components. This conclusion is supported by two lines of evidence: (1) no correlation between DMMW and O vii/O viii emission, which primarily traces dense disk regions; and (2) the comparison with electron density models, where DMMW aligns with models that incorporate both disk and halo components but significantly exceeds predictions from pure disk-only models, emphasizing the halo’s role. Furthermore, the lack of correlation with O viii absorption suggests that the primary temperature of the Galaxy’s hot gas is likely around 2×106 K or less, as traced by O vii absorption, while gas at higher temperatures (∼3–5 × 106 K) is present but less abundant. Our findings provide insights into the Milky Way’s gas distribution and improve DMMW estimates for future cosmological studies.

This is the Part II paper of our series of papers on a gauge-invariant perturbation theory on the Schwarzschild background spacetime. After reviewing our general framework of the gauge-invariant perturbation theory and the proposal of gauge-invariant treatments for l=0,1-mode perturbations on the Schwarzschild background spacetime in the Part I paper, we examine the linearized Einstein equations for even-mode perturbations. We discuss the strategy to solve the linearized Einstein equations for these even-mode perturbations including l=0,1 modes. Furthermore, we explicitly derive the l=0,1-mode solutions to the linearized Einstein equations in both the vacuum and the non-vacuum cases. We show that the solutions for l=0-mode perturbations includes the additional Schwarzschild mass parameter perturbation, which is physically reasonable. Then, we conclude that our proposal of the resolution of the l=0,1-mode problem is physically reasonable due to the realization of the additional Schwarzschild mass parameter perturbation and the Kerr parameter perturbation in the Part I paper.