Papers for Wednesday, Dec 27 2023

Planets are expected to conclude their growth through a series of giant impacts: energetic, global events that significantly alter planetary composition and evolution. Computer models and theory have elucidated the diverse outcomes of giant impacts in detail, improving our ability to interpret collision conditions from observations of their remnants. However, many open questions remain, as even the formation of the Moon, a widely suspected giant-impact product for which we have the most information, is still debated. We review giant-impact theory, the diverse nature of giant-impact outcomes, and the governing physical processes. We discuss the importance of computer simulations, informed by experiments, for accurately modeling the impact process. Finally, we outline how the application of probability theory and computational advancements can assist in inferring collision histories from observations, and we identify promising opportunities for advancing giant-impact theory in the future. $\bullet$ Giant impacts exhibit diverse possible outcomes leading to changes in planetary mass, composition, and thermal history depending on the conditions. $\bullet$ Improvements to computer simulation methodologies and new laboratory experiments provide critical insights into the detailed outcomes of giant impacts. $\bullet$ When colliding planets are similar in size, they can merge or escape one another with roughly equal probability, but with different effects on their resulting masses, densities, and orbits. $\bullet$ Different sequences of giant impacts can produce similar planets, encouraging the use of probability theory to evaluate distinct formation hypotheses.

We investigate how well the SPHEREx all-sky survey can constrain local primordial non-Gaussianity beyond the parameter $f_{\text{NL}}$ using the galaxy power spectrum. We forecast joint constraints on the parameters $f_{\text{NL}}$, $g_{\text{NL}}$ and $\tau_{\text{NL}}$ obtained assuming a simple two-field curvaton model of inflation. The parameters $f_{\text{NL}}$ and $g_{\text{NL}}$ characterise the squeezed limits of the primordial bispectrum and trispectrum respectively, and lead to a characteristic scale-dependence of the galaxy bias that increases out to arbitrarily large scales. Values of the parameter $\tau_{\text{NL}}> (\frac{6}{5}f_{\text{NL}})^{2}$ cause the galaxy power spectrum to have a stochastic component which also increases out to arbitrarily large scales. Our MCMC forecasts indicate that SPHEREx can provide joint constraints on any two of the three parameters $f_{\text{NL}}, \ g_{\text{NL}}$ and $\tau_{\text{NL}}$. Due to strong degeneracies among these parameters, measurements of the galaxy power spectra alone may not be sufficient to jointly constrain all three. Constraints on $f_{\text{NL}}, \ g_{\text{NL}}$ and $\tau_{\text{NL}}$ obtained from galaxy power spectrum observations depend on the modelling of underlying nuisance parameters. We study the robustness of our forecast constraints to modelling choices and note that even with relatively weak assumptions, SPHEREx galaxy power spectra can provide strong evidence of local non-Gaussianity, even if the particular values of $f_{\text{NL}}$ and $g_{\text{NL}}$ cannot be measured precisely.

One of the unique aspects of Earth is that it has a fractionally large Moon, which is thought to have formed from a Moon-forming disk generated by a giant impact. The Moon stabilizes the Earth's spin axis at least by several degrees and contributes to Earth's stable climate. Given that impacts are common during planet formation, exomoons, which are moons around planets in extrasolar systems, should be common as well, but no exomoon has been confirmed. Here we propose that an initially vapor-rich moon-forming disk is not capable of forming a large moon because growing moonlets, which are building blocks of a moon, experience strong gas drag and quickly fall toward the planet. Our impact simulations show that terrestrial and icy planets that are larger than $\sim 1.3-1.6 R_\oplus$ produce entirely vapor disks, which fail to form a large moon. This indicates that (1) our model supports the Moon-formation models that produce vapor-poor disks and (2) rocky and icy exoplanets whose radii are smaller than $\sim 1.6 R_\oplus$ are ideal candidates for hosting fractionally large exomoons.

We discuss the present state and planned updates of CosmoLattice, a cutting-edge code for lattice simulations of non-linear dynamics of scalar-gauge field theories in an expanding background. We first review current capabilities of the code, including the simulation of interacting singlet scalars and of Abelian and non-Abelian scalar-gauge theories. We also comment on new features recently implemented, such as the simulation of gravitational waves from scalar and gauge fields. Secondly, we discuss new extensions of CosmoLattice that we plan to release publicly. On the one hand, we comment on new physics modules, which include axion-gauge interactions $\phi F \widetilde{F}$, non-minimal gravitational couplings $\phi^2 R$, creation and evolution of cosmic defect networks, and magneto-hydro-dynamics (MHD). On the other hand, we discuss new technical features, including evolvers for non-canonical interactions, arbitrary initial conditions, simulations in 2+1 dimensions, and higher accuracy spatial derivatives.

We present the S-PLUS Transient Extension Program (STEP): a supernova and fast transient survey conducted in the southern hemisphere using data from the Southern Photometric Local Universe Survey (S-PLUS) Main Survey and the T80-South telescope. Transient astrophysical phenomena have a range of interest that goes through different fields of astrophysics and cosmology. With the detection of an electromagnetic counterpart to the gravitational wave (GW) event GW170817 from a binary neutron stars merger, new techniques and resources to study fast astrophysical transients in the multi-messenger context have increased. In this paper, we present the STEP overview, the SN follow-up data obtained, data reduction, analysis of new transients and deep learning algorithms to optimize transient candidate selection. Additionally, we present prospects and optimized strategy for the search of Gravitational Wave counterparts in the current LIGO/Virgo/Kagra observational run (O4) in the context of T80-South telescope.

Recent observations of the high-redshift universe have uncovered a significant number of active galactic nuclei, implying that supermassive black holes (SMBHs) would have to have been formed at much earlier times than expected. Direct collapse of metal-free gas clouds to SMBHs after recombination could help explain the early formation of SMBHs, but this scenario is stymied by the fragmentation of the clouds due to efficient molecular hydrogen cooling. We show that a subdominant population of tiny, evaporating primordial black holes, with significant clustering in some gas clouds, can heat the gas sufficiently so that molecular hydrogen is not formed, and direct collapse to to black holes is possible even at high redshifts.

Flare productivity varies among solar active regions (ARs). This study analyzed 20 ARs of contrasting sunspot areas and flare productivities to understand the super flare productivity of certain ARs. We used the flare index (FI) as an indicator of flare activity. We examined the pattern of morphological evolution of magnetic features. Further, we derived a set of magnetic feature parameters to quantitatively characterize ARs. Our study found that the correlation coefficient is the highest (r = 0.78) between FI and the length of the strong gradient polarity inversion line (SgPIL), while the coefficient is the lowest (r = 0.14) between FI and the total unsigned magnetic flux. For the selected ARs, this study also found that the super flare productive ARs have SgPILs (R value) longer (greater) than 50 Mm (4.5). These results suggest that flare productivity is mainly controlled by the size of the subregion that comprises close interaction of opposite magnetic polarities and is weakly correlated with the size of the whole ARs. Further, even though magnetic flux emergence is important, this study shows that it alone is insufficient to increase flare productivity. New emergence can drive either the interaction of like or opposite magnetic polarities of nonconjugate pairs (i.e., polarities not from the same bipole). In the former case, the magnetic configuration remains simple, and flare productivity would be low. In the latter case, the convergence of opposite magnetic fluxes of nonconjugate pairs results in a magnetic configuration with long SgPIL and an increase in flare productivity.

The far-infrared (IR) region is rich with information needed to characterize interstellar dust and to investigate the cold outer planets of the solar system and their icy moons. The proposed sub-orbital observatory the Balloon Experiment for Galactic INfrared Science (BEGINS) will utilize cryogenic instruments to map spectral energy distributions (SEDs) of interstellar dust in the Cygnus molecular cloud complex. A future high priority flagship mission Uranus Orbiter and Probe carrying a net flux radiometer (NFR) will study the in situ heat flux of the icy giants atmosphere to 10 bar pressure. These instruments require far-IR filters to define the instrument spectral bandwidths. Our ultimate goal is to define the instrument bands of BEGINS and the NFR with linear-variable filters (LVFs) and discrete-variable filters (DVFs). The LVFs and DVFs will be made of metal mesh band-pass filters (MMBF) comprised of a 100 nm thick gold film with cross-shaped slots of varying sizes along a silicon (Si) substrate with cyclic olefin copolymer (COC) anti-reflection (AR) coatings. We present our progress towards LVFs and DVFs with simulated and measured transmission of a room temperature, non-AR coated, single-band 44 $\mu$m MMBF filter. We have successfully fabricated, measured, and modeled a non-AR coated, room temperature 44 $\mu$m MMBF. The transmission at room temperature and non-AR coated was measured to be 27\% with a resolving power of 11. When COC-AR coated on both sides the transmission is expected to increase to 69\% with a resolving power of 10.

We present cosmological constraints from a joint analysis including the power spectrum and bispectrum of BOSS galaxies based on the Effective Field Theory of Large-Scale Structure predictions at one-loop order, in combination with CMB data from Planck, Supernovae from Pantheon+, and BAO from eBOSS and 6dF/MGS. Limits on $\Lambda$CDM parameters are in good agreement, and on average $\sim 5-10\%$ tighter, compared to former results including similar datasets but no bispectrum. Moreover, we find that galaxies at the three-point level with one-loop precision are decisive for the dark energy equation of state, constrained to be $w =-0.975 \pm 0.019$ at $68\%$CL. This value, consistent at $\sim 1.3\sigma$ with a cosmological constant, represents an improvement of about $140\%$ with respect to former determination. Our analyses illustrate the importance of beyond-two-point statistics at the highest reachable scales in constraining cosmological parameters, and in particular departure from $\Lambda$CDM.

Magnetized exoplanets can serve as the source of auroral radio emissions, allowing us to characterize the magnetospheric properties of these planets. Successful detections of auroral radio emissions from brown dwarfs, as well as from Jupiter, suggest that Jupiter-like planets in distant orbits may also generate radio emissions through a similar mechanism. In this study, we present our search for 250-500 MHz emissions from $\beta$ Pictoris b, one of the most extensively studied young Jupiter-like planets. We conducted the search using the upgraded Giant Metrewave Radio Telescope (uGMRT). Despite the favourable orbital inclination, no signal was detected, putting 3$\sigma$ upper limits on the radiation at 0.18 mJy. We translate this limit into constraints on the ionospheric and magnetospheric parameters, assuming that the emission is powered by the Hill current system. While the upper limit is larger by a factor of a few than the nominal estimate of radio intensity, we put constraints on the magnetospheric and ionospheric parameters.

We present a new approach for identifying neutrino flares. Using the unsupervised machine learning algorithm expectation maximization, we reduce computing times compared to conventional approaches by a factor of $10^5$ on a single CPU. Expectation maximization is also easily expandable to multiple flares. We explain the application of the algorithm and fit the neutrino flare of TXS 0506+056 as an example.

The very high energy (VHE) emission of the Central Molecular Zone (CMZ) is rarely modelled in 3D. Most approaches describe the morphology in 1D or simplify the diffusion to the isotropic case. In this work we show the impact of a realistic 3D magnetic field configuration and gas distribution on the VHE gamma-ray distribution of the CMZ. We solve the 3D cosmic-ray transport equation with an anisotropic diffusion tensor using the approach of stochastic differential equations as implemented in the CRPropa framework. We test two different source distributions for five different anisotropies of the diffusion tensor, covering the range of effectively fieldline-parallel diffusion to isotropic diffusion. Within the tested magnetic field configuration the anisotropy of the diffusion tensor is close to the isotropic case and three point sources within the CMZ are favoured. Future missions like the upcoming CTA will reveal more small-scale structures which are not jet included in the model. Therefor a more detailed 3D gas distribution and magnetic field structure will be needed.

Before the seasonal polar ice cap starts to expand towards lower latitudes on Mars, small frost patches may condensate out during the cold night and they may remain on the surface even during the day in shady areas. If ice in these areas can persist before the arrival of the contiguous ice cap, they may remain after the recession of it too, until the irradiation increases and the ice is met with direct sunlight. In case these small patches form periodically at the same location, slow chemical changes might occur as well. To see the spatial and temporal occurrence of such ice patches, large number of optical images should be searched for and checked. The aim of this study is to survey the ice condensation period on the surface with an automatized method using a Convolutional Neural Network (CNN) applied to High-Resolution Imaging Science Experiment (HiRISE) imagery from the Mars Reconnaissance Orbiter mission. The CNN trained to recognise small ice patches is automatizing the search, making it feasible to analyse large datasets. Previously a manual image analysis was conducted on 110 images from the southern hemisphere, captured by the HiRISE camera. Out of these, 37 images were identified with smaller ice patches, which were used to train the CNN. This approach is applied now to find further images with potential water ice patches in the latitude band between -40{\deg} and -60{\deg}, but contrarily to the training dataset recorded between 140-200{\deg} solar longitude, the images were taken from the condensation period between Ls = 0{\deg} to 90{\deg}. The model was ran on 171 new HiRISE images randomly picked from the given period between -40{\deg} and -60{\deg} latitude band, creating 73155 small image chunks. The model classified 2 images that show small, probably recently condensed frost patches and 327 chunks were predicted to show ice with more than 60% probability.

The collisional evolution of debris disks is expected to result in a characteristic wavy pattern of the grain size distributions, i.e., an under/overabundance of particles of specific sizes. This perturbed grain size distribution potentially leaves characteristic patterns in the spectral energy distribution (SED) of the disk system. We aim to quantify and understand the specific influence of discontinuous particle size distributions on the appearance of debris disks. For this purpose, we consider dust emission models based on two different grain size distributions, i.e., once with a single and once with a broken power law. We compare the spectral index $\alpha$ ($F_{\nu}\,\propto \nu^{\rm{\,\alpha}}$) in the case of a continuous grain size distribution with that of a discontinuous grain size distribution. We perform this comparison for central stars with different spectral types and two different disk structures (e.g., slim and broad debris dust rings). Within the considered parameter space, we find a characteristic difference between the spectral slopes of the SED in the different scenarios. More specifically, the overabundance of small grains leads to a steeper slope in the far-infrared/submillimeter regime, while the spectral index in the mm regime is hardly affected. On the other hand, the underabundance of medium-sized grains results in a slight steepening of the far-infrared slope of SED, while its primary effect is on the mm slope of SED, causing it to become shallower. We also find that the impact of an overabundance of small dust particles is more pronounced than that of an underabundance of medium-sized dust particles. Furthermore, we find that the difference between the spectral indices for the two different grain size distributions is largest for debris disks around brighter central stars and broader disks.

Fast Radio Bursts (FRBs) are millisecond-duration, bright ($\sim$Jy) extragalactic bursts, whose production mechanism is still unclear. Recently, a persistent radio source (PRS) of non-thermal origin was discovered to be physically associated to two of the repeating FRB sources. These two sources have unusually large Rotation Measure (RM) values likely tracing a dense magneto-ionic medium, consistent with a synchrotron radiation originating from a nebula surrounding the FRB source. Recent theoretical arguments predict that, if the observed RM mostly arises from the PRS region, there should be a simple relation between the luminosity of the PRS and the RM 8, 6. We report here the detection of a third, less luminous PRS associated with the nearby FRB 20201124A at a distance of 413 Mpc, significantly expanding the predicted relation into the low luminosity-low RM regime (<1000 rad/m2). At lower values of the RM, the radio luminosity falls below the limit of detection threshold for nowadays radio telescopes. These findings support the idea that the PRS is generated by a nebula in the FRB environment, and that most FRBs do not show a PRS because of a weaker magneto-ionic medium. This is generally consistent with models foreseeing a young magnetar as the central engine of the FRB, where the surrounding ionized nebula powers the PRS.

We investigate the interplay of phase mixing and the nonlinear turbulent cascade in the evolution and dissipation of Alfv\'en waves using compressible magnetohydrodynamics numerical simulations. We consider perturbations in the form of torsional waves, both propagating and standing, or turbulent fluctuations, or a combination of the two. The main purpose is to study how phase mixing and nonlinear couplings jointly work to produce small scales in different regimes. We conduct a numerical campaign to explore the typical parameters as the loop length, the amplitude and spatial profile of the perturbations, and the dissipative coefficients. A pseudo-spectral code is employed to solve the three-dimensional compressible magnetohydrodynamic equations, modeling the evolution of perturbations propagating in a flux tube corresponding to an equilibrium configuration with cylindrical symmetry. We find that phase mixing takes place for moderate amplitudes of the turbulent component even in a distorted, non-axisymmetric configuration, building small scales that are locally transverse to the density gradient. The dissipative time decreases with increasing the percentage of the turbulent component. This behavior is verified both for propagating and standing waves. Even in the fully turbulent case, a mechanism qualitatively similar to phase mixing occurs: it actively generates small scales together with the nonlinear cascade, thus providing the shortest dissipative time. General considerations are given to identify this regime in the parameter space. The turbulent perturbation also distorts the background density, locally increasing the Alfv\'en velocity gradient and further contributing to accelerating the formation of small scales.

The vertical shear instability (VSI) is a promising mechanism to drive turbulence in protoplanetary disks. Numerical simulations in literature demonstrate that the VSI non-linear saturation is predominated by the linear corrugation modes. These modes possess vertical wavelengths significantly longer than radial wavelengths. This paper aims to investigate the natural radial wavelengths of corrugation modes upon saturation, by a series of numerical simulations conducted in Athena++ at different grid resolutions, disk aspect ratios, and viscosity. We find a continuous reduction of radial wavelengths with grid resolution and a sign of convergence at 64 cells per scale height for fiducial models. Synthetic ALMA molecular line observations of $^{12}$CO(2-1) are performed to inspect the observability of corrugation modes feature, where it is washed out at above 32 cells per scale height. Flared and viscous disks that exhibit longer saturation wavelengths may mitigate the observation difficulty.

We present a time-dependent, one-dimensional magnetically driven disk-wind model based on magnetohydrodynamical (MHD) equations in the context of tidal disruption events (TDEs). We assume that the disk is geometrically thin and gas-pressure dominant and explicitly take into account magnetic braking as well as turbulent viscosity by an extended alpha viscosity prescription. We find a particular wind solution for a set of basic equations that satisfies the necessary and sufficient conditions for vertically unbound MHD flows. The solution demonstrates that the disk evolves with losing mass due to wind and accretion from the initial Gaussian density distribution. We confirm that the mass accretion rate follows the power law of time $t^{-19/16}$ at late times if the wind is absent, which corresponds to the classical solution of Cannizzo et al. (1990). We find that the mass accretion rate is steeper than the $t^{-19/16}$ curve if the disk wind is present. This is because the wind removes a significant fraction of the mass and angular momentum. Mass accretion is further induced by magnetic braking, known as a wind-driven accretion mechanism, resulting in more rapid decay with time in both the mass accretion and loss rates. The ultraviolet (UV) luminosity is the highest among the optical, UV, and X-ray luminosities from early to late evolutionary phases, suggesting optical and X-ray emissions from the disk are observationally insignificant due to magnetically driven winds in TDEs. Our model predicts that late-time bolometric light curves steeper than $t^{-19/16}$ in UV-bright TDEs potentially serve as compelling indicators for magnetically driven winds.

We investigate cosmological bounds on sterile neutrino masses in the light of the Hubble and $S_8$ tensions. We argue that non-zero masses for sterile neutrinos are inferred at 2$\sigma$ level in some extended models such as varying dark energy equation of state, when a direct measurement of the Hubble constant $H_0$ and weak lensing measurement of dark energy survey (DES) are taken into account. Furthermore, the Hubble and $S_8$ tensions are also reduced in such a framework. We also consider the case where a non-flat Universe is allowed and show that a slightly open Universe may be favored in models with sterile neutrinos in the context of the cosmological tensions.

Recent simulations show that the eccentricity of supermassive binary black hole with intermediate mass ratio could grow toward near unity through gravitational interaction with the stellar background in the merging remnant after two galaxies merge. The increased eccentricity reduces the timescale of the supermassive binary black hole merger through the strong gravitational radiation at periastron. Usually, large amount of gas flows toward the center of the newly merged galaxy, forming circumbinary gaseous disk around the binary in the center of the newly merged galaxy. Tidal interaction between such eccentric binary with intermediate mass ratio and circumbinary disk need to be investigated quantitatively. In this work, we study the gravitational interaction of the eccentric supermassive binary black hole with intermediate mass ratio and the circumbinary disk using code FARGO3D. Simulations are carried out with different semimajor, eccentricity and mass ratio. We find that the accretion rate onto the inner boundary could be strongly affected by the secondary black hole and tend to present periodic accretion rate in some situations. Such periodic accretion rate can be used as electromagnetic counterpart to the gravitational wave radiated by such kind of eccentric binary.

We confront massive Proca-Nuevo gravity with cosmological observations. The former is a non-linear theory involving a massive spin-1 field, that can be extended incorporating operators of the Generalized Proca class, and when coupled to gravity it can be covariantized in a way that exhibits consistent and ghost-free cosmological solutions, without experiencing instabilities and superluminalities at the perturbative level. When applied at a cosmological framework it induces extra terms in the Friedmann equations, however due to the special non-linear construction the field is eliminated in favor of the Hubble function. Thus, the resulting effective dark energy sector is dynamical, but with just one model parameter, namely the energy scale that controls the strength of the vector self-interactions. We use data from Supernovae Ia (SNIa) and Cosmic Chronometers (CC) observations and we construct the corresponding likelihood-contours for the free parameters. Interestingly enough, application of various information criteria, such as AIC, BIC and DIC, shows that the scenario of massive Proca-Nuevo gravity, although having exactly the same number of free parameters with {\Lambda}CDM concordance model, is more efficient in fitting the data. Finally, the reconstructed dark-energy equation-of-state parameter shows statistical compatibility with the model-independent, data-driven reconstructed one.

One of the most well-known extragalactic sources in the sky, quasar 3C 454.3, shows a curved parsec-scale jet that has been exhaustively monitored with very-long-baseline interferometry (VLBI) over the recent years. In this work, we present a comprehensive analysis of four years of high-frequency VLBI observations at 43 GHz and 86 GHz, between 2013-2017, in total intensity and linear polarization. The images obtained from these observations enabled us to study the jet structure and the magnetic field topology of the source on spatial scales down to 4.6 parsec in projected distance. The kinematic analysis reveals the abrupt vanishing of at least four new superluminal jet features in a characteristic jet region (i.e., region C), which is located at an approximate distance of 0.6 milliarcseconds from the VLBI core. Our results support a model in which the jet bends, directing the relativistic plasma flow almost perfectly toward our line of sight, co-spatially with the region where components appear to stop.

The light-curve evolution of a supernova contains information of the exploding star. Early-time photometry of a variety of explosive transients, including Calcium-rich transients and type IIb/Ibc and IIP supernovae shows evidence for an early light curve peak as a result of the explosion's shock wave passing through extended material (i.e., shock cooling emission (SCE)). Analytic modeling of the shock cooling emission allows us to estimate progenitor properties such as the radius and mass of extended material (e.g., the stellar envelope) as well as the shock velocity. In this work, we present a Python-based modular package that implements four analytic models originally developed in Piro 2015, Piro 2020 and Sapir & Waxman (2017) applied to photometric data to obtain progenitor parameter properties via different modeling techniques (including non-linear optimization, MCMC sampling). Our software is easily extendable to other analytic models for SCE and different methods of parameter estimation.

The spectroscopic performance of x-ray instruments can be affected at high count rates. The effects and mitigation in the optical chain, such as x-ray attenuation filters or de-focusing mirrors, are widely discussed, but those in the signal chain are not. Using the Resolve x-ray microcalorimeter onboard the XRISM satellite, we discuss the effects observed during high count rate measurements and how these can be modeled. We focus on three instrumental effects that impact performance at high count rate: CPU limit, pile up, and electrical cross talk. High count rate data were obtained during ground testing using the flight model instrument and a calibration x-ray source. A simulated observation of GX 13+1 is presented to illustrate how to estimate these effects based on these models for observation planning. The impact of these effects on high count rate observations is discussed.

Context. Three-dimensional (3D) reconnection is an important mechanism for efficiently releasing energy during astrophysical eruptive events, which is difficult to be quantitatively analyzed especially within turbulent plasmas. Aims. In this paper, an efficient method for identifying locations and configurations of 3D reconnection from MHD data is developed. Methods. This method analyzes the local nonideal electric field and magnetic structure at an arbitrary position. As only performing algebraical manipulations on the discrete field data and avoiding computationally expensive operations like field-line tracing and root-finding, this method naturally possesses high efficiency. To validate this method, we apply it to the 3D data from a high-resolution simulation of a Harris-sheet reconnection and a data-driven simulation of a coronal flux rope eruption. Results. It is shown that this method can precisely identify the local structures of discrete magnetic field. Through the information of nonideal electric field and the geometric attributes of magnetic field, the local structures of reconnection sites can be effectively and comprehensively determined. For fine turbulent processes, both qualitative pictures and quantitative statistical properties of small-scale reconnection structures can be obtained. For large-scale solar simulations, macro-scale magnetic structures such as flux ropes and eruption current sheets can also be recognized. Conclusions. We develop a powerful method to analyze multi-scale structures of 3D reconnection. It can be applied not only in MHD simulations but also in kinetic simulations, plasma experiments, and in-situ observations.

(abridged) We present the newly acquired data for an AstroSat/UVIT field centered on a face-on spiral starburst galaxy UGC 10420, located in the cluster Abell 2199. We have analysed the FUV data for this field along with the archival data from the Galex mission, optical photometric data from the SDSS, and low-frequency radio data from the LoTSS survey, respectively. The stars were separated from the galaxies using the SDSS pipeline classification, while the spectroscopic redshifts available for 35% of the detected UVIT sources were used to identify member galaxies of the cluster Abell 2199. We find that (a) the non-cluster galaxies are on average fainter than the cluster galaxies at fixed magnitude, (b) stars and galaxies are indistinguishable in the r vs NUV-r plane, and (c) bright stars are ~1.5 mag bluer than the galaxies in the FUV-r vs NUV-r colour-colour plane. Besides UGC 10420 which is the only known cluster galaxy with an extended-UV disk, we identify five more galaxies with asymmetric FUV morphology and extended radio emission in this field. All the asymmetric member galaxies of Abell 2199, lie within the virial boundaries of the cluster. This observation, together with the fact that these asymmetric cluster galaxies have low-frequency radio tails or FUV emission pointing away from the cluster centre leads us to hypothesise that these galaxies are likely undergoing ram-pressure stripping (RPS) under the influence of cluster-environment related mechanisms. A comparison of optical and FUV star formation rate of UVIT detected galaxies shows enhanced star formation in half of the RPS candidates, suggesting that environment-related mechanisms may lead to a burst of star formation in RPS galaxies. Our analysis indicates the presence of at least two more groups or clusters at z~0.077 and 0.260, coincident with Abell 2199 along the line of sight of the field of view studied here.

The solar cycle is generated by a magnetohydrodynamic dynamo mechanism, which involves the induction and recycling of the toroidal and poloidal components of the Sun's magnetic field. Recent observations indicate that the Babcock-Leighton mechanism -- mediated via the emergence and evolution of tilted bipolar active regions -- is the primary contributor to the Sun's large-scale dipolar field. Surface flux transport models and dynamo models have been employed to simulate this mechanism, which also allows for physics-based solar cycle forecasts. Recently, an alternative analytic method has been proposed to quantify the contribution of individual active regions to the Sun's dipole moment. Utilizing solar cycle observations spanning a century, here we test the efficacy of this algebraic approach. Our results demonstrate that the algebraic quantification approach is reasonably successful in estimating dipole moments at solar minima over the past century -- providing an independent verification of the Babcock-Leighton mechanism as the primary contributor to the Sun's dipole field variations. We highlight that this algebraic methodology stands as an independent approach for estimating the dipole moment at the minima of solar cycles, relying on characteristics of the sunspot cycle. We also show how this method may be utilized for solar cycle predictions; our estimate of the Sun's dipole field at the end of cycle 24 using this approach indicates that solar cycle 25 would be a moderately weak cycle, ranging between solar cycle 20 and cycle 24.

Low-surface-brightness galaxies (LSBGs), fainter members of the galaxy population, are thought to be numerous. However, due to their low surface brightness, the search for a wide-area sample of LSBGs is difficult, which in turn limits our ability to fully understand the formation and evolution of galaxies as well as galaxy relationships. Edge-on LSBGs, due to their unique orientation, offer an excellent opportunity to study galaxy structure and galaxy components. In this work, we utilize the You Only Look Once object detection algorithm to construct an edge-on LSBG detection model by training on 281 edge-on LSBGs in Sloan Digital Sky Survey (SDSS) $gri$-band composite images. This model achieved a recall of 94.64% and a purity of 95.38% on the test set. We searched across 938,046 $gri$-band images from SDSS Data Release 16 and found 52,293 candidate LSBGs. To enhance the purity of the candidate LSBGs and reduce contamination, we employed the Deep Support Vector Data Description algorithm to identify anomalies within the candidate samples. Ultimately, we compiled a catalog containing 40,759 edge-on LSBG candidates. This sample has similar characteristics to the training data set, mainly composed of blue edge-on LSBG candidates. The catalog is available online at https://github.com/worldoutside/Edge-on_LSBG.

Higher order clustering statistics of Ly$\alpha$ forest provide a unique probe to study non-gaussianity in Intergalactic matter distribution up to high redshifts and from large to small scales. The author presents a brief review of his work studying the spatial clustering properties of Ly$\alpha$ absorbers, with emphasis on 3-point statistics. The observational side of this involves redshift-space clustering of low-$z$ ($z<0.48$) and high-$z$ ($1.7<z<3.5$) Ly$\alpha$ absorbers. This is complemented with astrophysical inferences drawn from N-body hydrodynamical simulations. We also use simulations to study 2-point and 3-point clustering statistics in the transverse direction using projected QSO triplet sightlines. Such studies will become possible observationally with upcoming surveys.

The existence of accreting supermassive black holes up to billions of solar masses at early cosmological epochs (in the context of this work, redshifts z>=6) requires very fast growth rates which is challenging to explain. The presence of a relativistic jet can be a direct indication of activity and accretion status in active galactic nuclei (AGN), constraining the radiative properties of these extreme objects. However, known jetted AGN beyond z~6 are still very rare. The radio-emitting AGN J2331+1129 has recently been claimed as a candidate BL Lac object at redshift z=6.57, based on its synchrotron-dominated emission spectrum and the lack of ultraviolet/optical emission lines. It is a promising candidate for the highest-redshift blazar known to date. The aim of the observations described here was to support or refute the blazar classification of this peculiar source. We performed high-resolution radio interferometric imaging observations of J2331+1129 using the Very Long Baseline Array at 1.6 and 4.9 GHz in 2022 Feb. The images revealed a compact but slightly resolved, flat-spectrum core feature at both frequencies, indicating that the total radio emission is produced by a compact jet and originates from within a central 10-pc scale region. While these are consistent with the radio properties of a BL Lac object, the inferred brightness temperatures are at least an order of magnitude lower than expected from a Doppler-boosted radio jet, leaving the high-redshift BL Lac identification still an open question.

The low energy effective action of quantum gravity may include the higher curvature terms such as the Gauss-Bonnet term. The inflaton dynamics may be affected by the Gauss-Bonnet term if there is an inflaton-Gauss-Bonnet coupling. We show that an inflation model with a simple power law potential is made viable if it is coupled to the Gauss-Bonnet term since the prediction on the scalar spectral index and the tensor-to-scalar ratio are modified. We further point out that such a model predicts huge amount of gravitational waves at the high frequency range around 100GHz--100THz through the perturbative inflaton decay into gravitons induced by the Gauss-Bonnet term. Thus the spectrum of high frequency gravitational background is a unique feature of the inflation models with a Gauss-Bonnet correction.

Determining the precise ages of young (tens to a few hundred Myr) kinematic (``moving") groups is important for placing star, protoplanetary disk, and planet observations on an evolutionary timeline. The nearby $\sim$25 Myr-old $\beta$ Pictoris Moving Group (BPMG) is an important benchmark for studying stars and planetary systems at the end of the primordial disk phase. Gaia DR3 astrometry and photometry, combined with ground-based observations and more sophisticated stellar models, permit a systematic re-evaluation of BPMG membership and age. We combined Gaia astrometry with previously published radial velocities to evaluate moving group membership in a Bayesian framework. To minimize the effect of unresolved stellar multiplicity on age estimates, we identified and excluded multi-star systems using Gaia astrometry, ground-based adaptive optics imaging, and multi-epoch radial velocities, as well as literature identifications. We estimated age using isochrone and lithium-depletion-boundary fitting with models that account for the effect of magnetic activity and spots on young, rapidly rotating stars. We find that age estimates are highly model-dependent; Dartmouth magnetic models with ages of 23$\pm$8 Myr and 33$^{+9}_{-11}$ Myr provide best fits to the lithium depletion boundary and Gaia $M_G$ vs. $B_{P}$-$R_{P}$ color-magnitude diagram, respectively, whereas a Dartmouth standard model with an age of 11$^{+4}_{-3}$ Myr provides a best fit to the 2MASS-Gaia $M_{K_S}$ vs. $B_{P}$-$R_{P}$ color-magnitude diagram.

The similarity in physical conditions in winds of low-mass post-asymptotic giant branch stars and evolved massive stars leads to the appearance of an interesting phenomenon of spectral mimicry. Due to that the discovery of every new star with Wolf--Rayet spectrum requires special study of its evolutionary status before it may be included in the list of Galactic Wolf--Rayet (WR) stars. A couple of years ago LAMOST J040901.83+323955.6 (hereafter J0409+3239) was selected as a WR star in LAMOST spectroscopic database by machine learning methods. In this work we investigated its evolutionary status. Analyzing the spatial location of J0409+3239, in the Galaxy and its position in the color-magnitude diagram we concluded what J0409+3239, is instead a low mass object with WR phenomenon. Its luminosity is $L*=1000 L_\odot$ and effective temperature $T_{\rm eff}$=40,000 K. Using new and archival photometric data we detected irregular variability on time scales from hours to tens of days with amplitude up to $\approx0.2$ mag. Comparison of the spectrum obtained in 2022 with the one from 2014 also shows an evidence of spectral variability. The absence of clearly detected circumstellar nebula does not allow to classify J0409+3239, as [WR], i.e. a central star of planetary nebula (CSPN). However, its position in Hertzsprung--Russell diagram suggests that J0409+3239, is a low mass star caught in rare transitional phase to CSPN. Estimation of J0409+3239, mass based on evolutionary tracks shows that it is less than $0.9~M_\odot$, and thus the age of the Galaxy is barely enough for the star to evolve to its current stage.

This paper investigates the number of scatterings a photon undergoes in random walks before escaping from a medium. The number of scatterings in random walk processes is commonly approximated as $\tau+\tau^2$ in the literature, where $\tau$ is the optical thickness measured from the center of the medium. However, it is found that this formula is not accurate. In this study, analytical solutions in sphere and slab geometries are derived for both optically thin and optically thick limits, assuming isotropic scattering. These solutions are verified using Monte Carlo simulations. In the optically thick limit, the number of scatterings is found to be $0.5\tau^2$ and $1.5\tau^2$ in a sphere and slab, respectively. In the optically thin limit, the number of scatterings is $\approx\tau$ in a sphere and $\approx\tau(1-\gamma-\ln\tau+\tau)$ in a slab, where $\gamma\simeq 0.57722$ is the Euler-Mascheroni constant. Additionally, we present approximate formulas that reasonably reproduce the simulation results well in intermediate optical depths. These results are applicable to scattering processes that exhibit forward and backward symmetry, including both isotropic and Thomson scattering.

The unique biosignature of life on Earth is the homochirality of organic compounds such as amino acids, proteins, and sugars. The origin of this homochirality has remained a mystery for over a century. While high-energy spin-polarized (spin-up or spin-down) electrons (SPEs) from the $\beta$ decay of radioactive nuclei discovered by Lee and Yang (1956) and Wu et al. (1957) have been proposed as a potential source of symmetry breaking, their exact role on homochirality is much debated. Here we suggest magnetically aligned dust grains as a new source of SPEs due to photoemission of electrons having aligned spins by the Barnett effect. For the interstellar UV radiation field of strength $G_{\rm UV}$, we found that the SPE emission rate is $\Gamma_{\rm pe}^{\rm SPE}\sim 10^{-14}G_{\rm UV}$ electrons per second per H, the fraction of spin-polarized to total photoelectrons is $\sim 10\%$, and the SPE yield (photoelectron number per UV photon) can reach $\sim 1\%$, using the modern theory of grain alignment. Low-energy SPEs from aligned grains would cause chiral symmetry breaking of interstellar chiral molecules due to spin-selective (dipole-dipole) interactions. Finally, we suggest magnetically aligned grains as chiral agents that facilitate and enrich the chiral asymmetry of chiral molecules. Our proposed mechanism might explain the detection of chiral asymmetry in the ISM, comets, and meteorites due to the ubiquitous UV radiation and magnetically aligned grains, paving the way for understanding the origin and distribution of life in the universe. This mechanism based on magnetic grain alignment implies the role of magnetic fields on chirality symmetry breaking.

Active galactic nucleus (AGN) driven outflows can have a significant impact on the evolution of the host galaxy. In this work, we compare the properties of galaxies that hosts AGNs with and without outflows. Our sample consists of 103 AGNs identified by mid-IR color-color selection, and confirmed with optical spectroscopy at a redshift range of 0.3 $\lesssim$ z $\lesssim$ 0.9. We fit the [OIII] $\lambda$5007 line using spectra from the zCOSMOS survey to identify and to study the occurrence of outflows. We find that ionized outflows are present in $\sim$25\% of our sample, with the largest incidence at the highest [OIII] and X-ray luminosity bins. The fastest outflows are found in the more extended and massive galaxies. We do not observe a difference in the star formation rate of AGNs with outflows compared to AGNs without outflows. From visual inspection and non-parametric morphological studies, we obtain that outflows are preferentially observed in galaxies with disk-type and elliptical morphologies.

This paper investigates the problem of estimating three stellar atmospheric physical parameters and thirteen elemental abundances for medium-resolution spectra from Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST). Typical characteristics of these spectra are their huge scale, wide range of spectral signal-to-noise ratios, and uneven distribution in parameter space.These characteristics lead to unsatisfactory results on the spectra with low temperature, high temperature or low metallicity.To this end, this paper proposes a Stellar Parameter Estimation method based on Multiple Regions (SPEMR) that effectively improves parameter estimation accuracy. On the spectra with {S/N $\geq 10$}, the precisions are 47 K, 0.08 dex, 0.03 dex respectively for the estimations of ($T_{\rm eff}$, $\log \,g$ and $\rm [Fe/H]$), 0.03 dex to 0.06 dex for elements C, Mg, Al, Si, Ca, Mn and Ni, 0.07 dex to 0.13 dex for N, O, S, K and Ti, while that of Cr is 0.16 dex.For the reference of astronomical science researchers and algorithm researchers, we released a catalog for 4.19 million medium-resolution spectra from the LAMOST DR8, experimental code, trained model, training data, and test data.

The bispectrum, the three-point correlation in Fourier space, is a crucial statistic for studying many effects targeted by the next-generation galaxy surveys, such as primordial non-Gaussianity (PNG) and general relativistic (GR) effects on large scales. In this work we develop a formalism for the bispectrum in the Spherical Fourier-Bessel (SFB) basis - a natural basis for computing correlation functions on the curved sky, as it diagonalizes the Laplacian operator in spherical coordinates. Working in the SFB basis allows for line-of-sight effects such as redshift space distortions (RSD) and GR to be accounted for exactly, i.e without having to resort to perturbative expansions to go beyond the plane-parallel approximation. Only analytic results for the SFB bispectrum exist in the literature given the intensive computations needed. We numerically calculate the SFB bispectrum for the first time, enabled by a few techniques: We implement a template decomposition of the redshift-space kernel $Z_2$ into Legendre polynomials, and separately treat the PNG and velocity-divergence terms. We derive an identity to integrate a product of three spherical harmonics connected by a Dirac delta function as a simple sum, and use it to investigate the limit of a homogeneous and isotropic Universe. Moreover, we present a formalism for convolving the signal with separable window functions, and use a toy spherically symmetric window to demonstrate the computation and give insights into the properties of the observed bispectrum signal. While our implementation remains computationally challenging, it is a step toward a feasible full extraction of information on large scales via a SFB bispectrum analysis.

Aims. We investigate the role of photo-evaporation of dust exposed to the radiation field from hot young stars and planetary nebulae (PNe) as a possible destruction mechanism of dust grains in the interstellar medium (ISM). Methods. We estimate photo-evaporation induced by the feedback of individual or clustered young stars, of PNe and in the presence of a variable radiation field scaled with the interstellar radiation field. For PNe we investigate dust photo-evaporation of both dust grains already present in the ISM as well as those formed in the last phases of the evolution of thermally pulsing asymptotic giant branch (TP-AGB) stars. We include dust photo-evaporation rate in models of dust evolution in galaxies for different assumptions of the dust growth scenario, dust-to-gas ratios, star formation histories, and initial mass functions of the stars. Results. For all the cases considered, we find that both photo-evaporation from young stars and from PNe are negligible with respect to other dust removal processes such as destruction from supernovae shocks, astration and possibly outflow. Grains are stable against photo-evaporation if they are exposed to a radiation field which is up to 10^7 times the interstellar radiation field. Conclusions. Dust grains of size >= 0.01 microns are not efficiently destroyed by photo-evaporation also in the presence of a strong radiation field.

We examine the effect of variable viscosity parameter ($\alpha$) in relativistic, low angular momentum advective accretion flow around rotating black holes. Following the recent simulation studies of magnetohydrodynamic disk that reveal the radial variation of $\alpha(r)$, we theoretically investigate the properties of the global transonic accretion flow considering a one-dimensional power law prescription of viscosity parameter as $\alpha(r) \propto r^{\theta}$, where the viscosity exponent $\theta$ is a constant. In doing so, we adopt the relativistic equation of state and solve the fluid equations that govern the flow motion inside the disk. We find that depending on the flow parameters, accretion flow experiences centrifugally supported shock transition and such shocked accretion solutions continue to exist for wide ranges of the flow energy, angular momentum, accretion rate and viscosity exponent, respectively. Due to shock compression, the hot and dense post-shock flow (hereafter PSC) can produce the high energy radiations after reprocessing the soft photons from the pre-shock flow via inverse Comptonization. Since PSC is usually described using shock radius ($r_s$), compression ratio ($R$) and shock strength ($S$), we study the role of $\theta$ in deciding $r_s$, $R$ and $S$, respectively. Moreover, we obtain the parameter space for shock and find that possibility of shock formation diminishes as $\theta$ is increased. Finally, we compute the limiting value of $\theta$ ($i.e., \theta^{\rm max}$) that admits shock and find that flow can sustain more viscosity when it accretes onto rapidly rotating ($a_{\rm k} \rightarrow 1$) black hole in comparison to weakly rotating ($a_{\rm k} \rightarrow 0$) black hole.

Context. The Galactic centre is hazardous for stellar clusters because of the strong tidal force. Supposedly, many clusters were destroyed and contributed stars to the crowded stellar field of the bulge and the nuclear stellar cluster. However, it is hard to develop a realistic model to predict the long-term evolution of the complex inner Galaxy, and observing surviving clusters in the central region would provide crucial insights into destruction processes. Aims. Among hitherto-known Galactic globular clusters, VVV CL002 is the closest to the centre, 0.4 kpc, but has a very high transverse velocity, 400 km s$^{-1}$. The nature of this cluster and its impact on Galactic astronomy need to be addressed with spectroscopic follow-up. Methods. Here we report the first measurements of its radial velocity and chemical abundance based on near-infrared high-resolution spectroscopy. Results. We found that this cluster has a counterrotating orbit constrained within 1.0\,kpc of the centre, as close as 0.2 kpc at the perigalacticon, confirming that the cluster is not a passerby from the halo but a genuine survivor enduring the harsh conditions of the Galactic mill's tidal forces. In addition, its metallicity and $\alpha$ abundance ([$\alpha$/Fe] $\simeq +0.4$ and [Fe/H]$=-0.54$) are similar to some globular clusters in the bulge. Recent studies suggest that stars with such $\alpha$-enhanced stars were more common at 3 - 6 kpc from the centre around 10 Gyrs ago. Conclusions. We infer that VVV CL002 was formed outside but is currently falling down to the centre, exhibiting a real-time event that must have occurred to many clusters a long time ago.

Lyman-Alpha Emitting galaxies (LAEs) are typically young, low-mass, star-forming galaxies with little extinction from interstellar dust. Their low dust attenuation allows their Ly$\alpha$ emission to shine brightly in spectroscopic and photometric observations, providing an observational window into the high-redshift universe. Narrowband surveys reveal large, uniform samples of LAEs at specific redshifts that probe large scale structure and the temporal evolution of galaxy properties. The One-hundred-deg$^2$ DECam Imaging in Narrowbands (ODIN) utilizes three custom-made narrowband filters on the Dark Energy Camera (DECam) to discover LAEs at three equally spaced periods in cosmological history. In this paper, we introduce the hybrid-weighted double-broadband continuum estimation technique, which yields improved estimation of Ly$\alpha$ equivalent widths. Using this method, we discover 6339, 6056, and 4225 LAE candidates at $z =$ 2.4, 3.1, and 4.5 in the extended COSMOS field ($\sim$9 deg$^2$). We find that [O II] emitters are a minimal contaminant in our LAE samples, but that interloping Green Pea-like [O III] emitters are important for our redshift 4.5 sample. We introduce an innovative method for identifying [O II] and [O III] emitters via a combination of narrowband excess and galaxy colors, enabling their study as separate classes of objects. We present scaled median stacked SEDs for each galaxy sample, revealing the overall success of our selection methods. We also calculate rest-frame Ly$\alpha$ equivalent widths for our LAE samples and find that the EW distributions are best fit by exponential functions with scale lengths of $w_0$ = 55 $\pm$ 1, 65 $\pm$ 1, and 62 $\pm$ 1 Angstroms, respectively.

Recent observations of high-energy neutrinos by IceCube and gamma rays by the Fermi Large Area Telescope (LAT) and the MAGIC telescope have suggested that neutrinos are produced in gamma-ray opaque environments in the vicinity of supermassive black holes. In this work, we present 20 MeV - 1 TeV spectra of three Seyfert galaxies whose nuclei are predicted to be active in neutrinos, NGC 4151, NGC 4945 and the Circinus Galaxy, using 14.4 years of the Fermi LAT data. In particular, we find evidence of sub-GeV excess emission that can be attributed to gamma rays from NGC 4945, as was also seen in NGC 1068. These spectral features are consistent with predictions of the magnetically-powered corona model, and we argue that NGC 4945 is among the brightest neutrino active galaxies detectable for KM3Net and Baikal-GVD. On the other hand, in contrast to other reported results, we do not detect gamma rays from NGC 4151, which constrains neutrino emission from the accretion shock model. Future neutrino detectors such as IceCube-Gen2 and MeV gamma-ray telescopes such as AMEGO-X will be crucial for discriminating among the theoretical models.

Symbiotic binaries exhibit a wide range of photometric variability spanning different timescales attributed to orbital motion, intrinsic variability of individual components, or the interaction between the two stars. In the range from minutes to hours, variability induced by accretion processes, likely originating from the accretion disks, denoted as flickering, is detected. This variability could mimic solar-like oscillations exhibited by luminous red giants. We aim to investigate whether it is possible to utilize the precise observations of the NASA TESS mission to detect flickering in symbiotic stars despite such studies being usually performed at shorter wavelengths. Additionally, our goal is to develop a quantitative method for the detection of accretion-induced flickering that does not rely solely on subjective assessment of the light curves. We obtain the light curves of known symbiotic stars and a comprehensive control sample of assumed single red giants from the TESS FFIs. From the processed light curves and their PSD, we measure the amplitudes of the variability and other parameters. We introduce a method that enables the differentiation between flickering sources and stars that do not exhibit this variability. We detect flickering-like variability in 20 symbiotic stars utilizing TESS data, with 13 of them being previously unidentified as flickering sources. Moreover, the TESS observations facilitate the detection of related variations occurring over timescales of a few days, as well as changes in the flickering behavior across multiple sectors. The flickering has now been likely detected in a total of 35 known symbiotic stars. When focusing solely on accreting-only symbiotic stars where the detection of flickering is presumably more straightforward, the fraction could reach as high as ~80%. This suggests that accretion disks may be rather prevalent in these binaries.

In this work, we study the dynamics of rotation of the small satellites Methone and Aegaeon and revisit previous works on the rotation of Prometheus, Metis, and Amalthea. In all cases, the surfaces of section computed with the standard spin-orbit model reveal that the synchronous regime shares another large domain in the rotation phase space. We reproduce and apply the hamiltonian theory given in Wisdom (2004) to analytically characterize the detected structure as being a secondary resonance where the period of oscillations around the synchronism is similar to the orbital period. Being that the current rotational states of this sort of satellite should be synchronous (Thomas and Helfenstein 2020), our results can be taken into account in evolutionary studies of their rotation.

Causal relationships in conformal geometry are used to analyze angular boundaries of cosmic microwave background (CMB) correlations. It is shown that curvature correlations limited to timelike intervals on world lines that have connected causal diamonds during inflation generate an angular correlation function $C(\Theta)$ of gravitationally-induced CMB anisotropy that vanishes in a range of angular separation from $\Theta= \pi/2 - \arcsin(1/4)$ to as far as $\Theta=3\pi/4$. This model-independent symmetry is shown to agree remarkably well with even-parity and dipole-corrected CMB correlations measured in all-sky maps from the WMAP and Planck satellites. Realizations of the standard quantum field theory cosmological model are shown to produce comparably small correlation with probabilities ranging from $\simeq 10^{-4.3}$ to $\simeq 10^{-1.5}$, depending on the map and range of angular separation. These measurements are interpreted as evidence for a causal symmetry based on a basic physical principle not included in the effective field theory approximation to cosmological quantum gravity: quantum fluctuations only generate physical correlations of spacetime curvature within regions bounded by causal diamonds. Theoretical implications and further cosmological tests of this interpretation are briefly discussed.

Horizon-scale observations from the Event Horizon Telescope (EHT) have enabled precision study of supermassive black hole accretion. Contemporary accretion modeling often treats the inflowing plasma as a single, thermal fluid, but microphysical kinetic effects can lead to significant deviations from this idealized picture. We investigate how the helicity barrier influences EHT-accessible electromagnetic observables by employing a simple model for electron heating based on kinetic physics and the cascade of energy and helicity in unbalanced turbulence. Although the helicity barrier plays only a minor role in regions with high plasma-beta, like in SANE disks, it may substantially impact in regions with more ordered magnetic fields, such as the jet and its surrounding wind in SANE flows as well as throughout the entire domain in MAD flows. In SANE flows, emission shifts from the funnel wall towards the lower-magnetization disk region; in MAD flows the emission morphology remains largely unchanged. Including the helicity barrier leads to characteristically lower electron temperatures, and neglecting it can lead to underestimated accretion rates and inferred jet powers. The corresponding higher plasma densities result in increased depolarization and Faraday depths thereby decreasing the amplitude of the beta_2 coefficient while leaving its angle unchanged. Both the increased jet power and lower |beta_2| may help alleviate outstanding tensions between modeling and EHT observations. We also find that the estimated ring diameter may be underestimated when the helicity barrier is neglected. Our results underscore the significance of the helicity barrier in shaping black hole observables and inferred accretion system parameters.

Experiments searching for weakly interacting massive particle dark matter are now detecting background events from solar neutrino-electron scattering. However, the dominant background in state-of-the-art experiments such as LZ and XENONnT is beta decays from radon contamination. In spite of careful detector material screening, radon progenitor atoms are ubiquitous and long-lived, and radon is extremely soluble in liquid xenon. We propose a change of phase and demonstrate that crystalline xenon offers more than a factor x500 exclusion against radon ingress, compared with the liquid state. This level of radon exclusion would allow crystallized versions of existing experiments to probe spin-independent cross sections near 1e-47 cm2 in roughly 11 years, as opposed to the 35~years required otherwise.

We use publicly-available data to perform a search for correlations of high energy neutrino candidate events detected by IceCube and high-energy photons seen by the HAWC collaboration. Our search is focused on unveiling such correlations outside of the Galactic plane. This search is sensitive to correlations in the neutrino candidate and photon skymaps which would arise from a population of unidentified point sources. We find no evidence for such a correlation, but suggest strategies for improvements with new data sets.

Shadow detection and removal is a challenging problem in the analysis of hyperspectral images. Yet, this step is crucial for analyzing data for remote sensing applications like methane detection. In this work, we develop a shadow detection and removal method only based on the spectrum of each pixel and the overall distribution of spectral values. We first introduce Iterative Logistic Regression (ILR) to learn a spectral basis in which shadows can be linearly classified. We then model the joint distribution of the mean radiance and the projection coefficients of the spectra onto the above basis as a parametric linear combination of Gaussians. We can then extract the maximum likelihood mixing parameter of the Gaussians to estimate the shadow coverage and to correct the shadowed spectra. Our correction scheme reduces correction artefacts at shadow borders. The shadow detection and removal method is applied to hyperspectral images from MethaneAIR, a precursor to the satellite MethaneSAT.

The equation of state (EOS) of dense nuclear matter is a key factor to determine the internal structure and properties of neutron stars. However, the EOS of high-density nuclear matter has great uncertainty mainly because the terrestrial nuclear experiments cannot reproduce matter as dense as that in the inner core of a neutron star. Fortunately, continuous improvements in astronomical observations of neutron stars provide the opportunity to inversely constrain the EOS of high-density nuclear matter. A number of methods have been proposed to implement this inverse constraint, such as the Bayesian analysis algorithm, the Lindblom's approach, and so on. Neural network algorithm is an effective new method developed in recent years. By employing a set of isospin-dependent parametric EOSs as the training sample of neural network algorithm, we set up an effective way to reconstruct the EOS with relative accuracy through a few mass-radius data. Based on the obtained neural network algorithms and according to the NICER observations on masses and radii of neutron stars with assumed precision, we get the inversely constrained EOS and further calculate the corresponding macroscopic properties of the neutron star. The results are basically consistent with the constraint on EOS from the Huth $et~ al.$ based on Bayesian analysis. Moreover, the results show that even though the neural network algorithm was obtained by using the finite parameterized EOS as the training set, it is valid for any rational parameter combination of the parameterized EOS model.

Metastable cosmic strings appear in models of new physics with a two-step symmetry breaking $G\to H\to 1$, where $\pi_1(H)\neq 0$ and $\pi_1(G)=0$. They decay via the monopole-antimonopole pair creation inside. Conventionally, the breaking rate has been estimated by an infinitely thin string approximation, which requires a large hierarchy between the symmetry breaking scales. In this paper, we reexamine it by taking into account the finite sizes of both the cosmic string and the monopole. We obtain a robust lower limit on the tunneling factor $e^{-S_B}$ even for regimes the conventional estimate is unreliable. In particular, it is relevant to the cosmic string interpretation of the gravitational wave signals recently reported by pulsar timing array experiments.

The gravitational lensing of supermassive black holes surrounded by dark matter halo has attracted a great number of interests in recent years. However, many studies employed simplified dark matter density models, which makes it very hard to give a precise prediction on the dark matter effects in real astrophysical galaxies. In this work, to more accurately describe the distribution of dark matter in real astrophysical galaxies, we study the gravitational lensing of black holes in astrophysical dark matter halo models (Beta, Burkert, Brownstein, and Moore). The deflection angle is obtained using a generalized Gibbons-Werner approach. The visual angular positions and the Einstein rings are also calculated by adopting the gravitational lens equation. Specifically, we choose the supermassive black holes in Milky Way Galaxy, Andromeda galaxy (M31), Virgo galaxy (M87), and ESO138-G014 galaxy as examples, including the corresponding fitted value of dark matter halos. The results suggest that the dark matter halo described by the Beta model has non-negligible influences on the gravitational deflection angle and gravitational lensing observations. However, the Burkert, Brownstein, and Moore models have relatively small influences on angular position of images and the Einstein ring.

We construct Barrow holographic dark energy with varying exponent. Such an energy-scale-dependent behavior is typical in quantum field theory and quantum gravity under renormalization group considerations, however in the present scenario it has an additional justification, since in realistic cases one expects that Barrow entropy quantum-gravitational effects to be stronger at early times and to smooth out and disappear at late times. We impose specific, redshift-dependent ans\"{a}tze for the Barrow running exponent, such as the linear, CPL-like, exponential, and trigonometric ones, and we investigate their cosmological behavior. We show that we can recover the standard thermal history of the universe, with the sequence of matter and dark energy epochs, in which the transition from deceleration to acceleration happens at $z\approx 0.65$, in agreement with observations. In the most realistic case of hyperbolic tangent ansatz, in which we can easily bound Barrow exponent inside its theoretically determined bounds 0 and 1 for all redshifts, we see that the dark-energy equation-of-state parameter can be quintessence like, or experience the phantom-divide crossing, while in the future it can either tend to the cosmological constant value or start increasing again. All these features reveal that Barrow holographic dark energy with varying exponent is not only theoretically more justified than the standard, constant-exponent case, but it leads to richer cosmological behavior too.

The target auditory of scientific outreach efforts is often limited to the small enthusiastic subset of the society that value science and actively seeks knowledge. However, the vast majority is usually indifferent or in some cases may even be opposed to sciences. To bring these people around to support sciences, we have to double and triple our efforts. I describe my personal experience how I reach out to them by means of popular articles in glossy magazines - not the most common outreach venue, at least in Bulgaria. Four years of writing have though me that the key for success is to turn the science into and engaging human story that will keep the readers curious until the revelation of the riddle at the end of the last paragraph. Next, come the spectacular visuals - for the modern reader, spoiled by eye candies of Internet and Hollywood they are almost as important as the written words. The final requirement is accessibility - an article should explain well only two or three concepts; I am not calling for simplicity but for measuring and structuring of the information content - it is better to give the readers two understandable pieces that they would enjoy instead one impenetrable article that would turn them away from popular science for good.

Orbiting low frequency antennas for radio astronomy (OLFAR) that capture cosmic signals in the frequency range below 30MHz could provide valuable insights on our Universe. These wireless swarms of satellites form a connectivity graph that allows data exchange between most pairs of satellites. Since this swarm acts as an interferometer, the aim is to compute the cross-correlations between most pairs of satellites. We propose a k-nearest-neighbour communication protocol, and investigate the minimum neighbourhood size of each satellite that ensures connectivity of at least 95% of the swarm. We describe the proportion of cross-correlations that can be computed in our method given an energy budget per satellite. Despite the method's apparent simplicity, it allows us to gain insight into the requirements for such satellite swarms. In particular, we give specific advice on the energy requirements to have sufficient coverage of the relevant baselines.

We show analytically that there exist compact stellar objects akin to neutron stars whose radius is smaller than the Schwarzschild radius defined by Arnowitt-Deser-Misner (ADM) mass. The radius of the compact object is defined by the radius where the energy density and the pressure of ordinary matter vanish, while clouds of scalar(s) can extend beyond this radius -- a situation that is often encountered in modified gravity theories, like $F(R)$ gravity and the scalar--Einstein--Gauss-Bonnet gravity. The clouds of scalar mode(s) give additional contributions to the ADM mass and as a result, the corresponding Schwarzschild radius given by the ADM mass can be larger than that of the compact object.

We generalize the notion of Einstein-Rosen bridge by defining it as a space-ilke connection between two universes with regions of asymptotically minkowskian space-time infinities. The corresponding symmetry and asymmetry properties of the generalized Einstein-Rosen bridge are considered at the cases of Reissner-Nordstr\"om and Kerr metrics. We elucidate the versatility of intriguing symmetry and asymmetry phenomena outside and inside black holes. For description of the test particle (planet and photon) motion it is used the Kerr-Newman metric of the rotating and electrically charged black hole. In particular, it is demonstrated the symmetry and asymmetry of the one-way Einstein-Rosen bridge inside black hole toward and through the plethora of endless and infinite universes.

We study conformal transformations in the most general parity-preserving models of the New General Relativity type. Then we apply them to analysis of cosmological perturbations in the (simplest) spatially flat cosmologies. Strong coupling issues around Minkowski spacetime are seen for many special cases of these models. At the same time, the behaviour of the most general three-parameter case seems to be very robust, presumably always with only the eight first-class constraints coming from diffeomorphisms. Also the case of the so-called 1-parameter New GR doesn't show any discontinuity between Minkowski and the cosmology, though without showing any deviations from GR which would be observable at this level either.

We modify the symmetric-teleparallel dark energy through the addition of a further Yukawa-like term, in which the non-metricity scalar, $Q$, is non-minimally coupled to a scalar field Lagrangian where the phion acts as quintessence, describing dark energy. We investigate regions of stability and find late-time attractors. To do so, we conduct a stability analysis for different types of physical potentials describing dark energy, namely the power-law, inverse power-law, and exponential potentials. Within these choices, we furthermore single out particular limiting cases, such as the constant, linear and inverse potentials. For all the considered scenarios, regions of stability are calculated in terms of the signs of the coupling constant and the exponent, revealing a clear degeneracy among coefficients necessary to ensure stability. We find that a generic power-law potential with $\alpha > 0$ is not suitable as a non-minimal quintessence potential and we put severe limits on the use of inverse potential, as well. In addition, the equations of state of each potential have been also computed. We find the constant potential seems to be favored than other treatments, since the critical point appears independent of the non-minimal coupling.

We study the collisions of elastic superconducting strings, also referred to as current-carrying strings, formed in a $U_{\rm local}(1) \times U_{\rm global}(1)$ field-theory model, using three-dimensional numerical field-theoretic simulations. The breaking of Ulocal(1) leads to string formation via the Higgs mechanism, while the scalar field of the second Uglobal(1) carries the current, which condenses onto the string. We construct straight and static superconducting string solutions numerically and identify the regions in which they exist in the model parameter space. We then perform dynamical simulations for colliding superconducting strings with various collision angles and collision velocities. We explore the kinematic parameter space for six sets of model parameters characterising the coupling between the two scalar fields and the current on the string. The final states of the strings (after the collision) are reported diagrammatically. We classify them into four categories: (i) regular intercommutation, (ii) double intercommutation, (iii) bound state, and (iv) expanding string solution. We find that the outcome of the collision process is the regular intercommutation of the colliding strings in most of the kinematic parameter space while they form bound states for small velocities and small angles. We also find that the strings undergo two successive intercommutations and therefore pass through one other in a small region corresponding to relatively small angles and velocities of order c/2. The string structure breaks down when there is a relatively large coupling between the two scalar fields even if each string is stable before the occurrence of the collision.

We present a significant extension of the quark mass density-dependent model (QMDDM), initially revised in our prior study (Lugones and Grunfeld, Phys. Rev. D 107, 043025 (2023)), where thermodynamic inconsistencies were addressed. Our current work enriches the QMDDM by incorporating excluded volume effects, as a step towards a more realistic representation of the quark matter equation of state (EOS) at zero temperature. We introduce the concept of ``available volume'' in the Helmholtz free energy formulation, accounting for the space excluded by each quasiparticle due to its finite size or repulsive interactions. We present a methodology to modify the EOS for point-like particles, allowing for a simple and direct incorporation of excluded volume effects. This is first addressed in a simple one-flavor model and then extended to a more realistic three-flavor system, incorporating both mass and volume dependencies on the baryon number density. We examine various ansatzes for the excluded volume, ultimately adopting one that aligns with the asymptotic freedom behavior of Quantum Chromodynamics (QCD). The EOS for electrically neutral systems in chemical equilibrium is computed, focusing on self-bound and hybrid matter scenarios. We show that the incorporation of excluded volume effects renders the EOS stiffer and that excluded volume effects are essential to align the mass-radius relation of self-bound and hybrid stars with modern astrophysical constraints.