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Radio pulsars can power their coherent radio emission through intermittent plasma discharges in magnetospheric gaps. The nonlinear coupling between particle acceleration, quantum electrodynamic (QED) processes, and electric field screening remains difficult to model self-consistently. We present an analytical concurrency model and first-principles particle-in-cell (PIC) simulations of polar cap discharges. The model predicts limit-cycle behavior where the electric field and plasma density oscillate with a frequency set by the local plasma frequency, modified by the plasma inertia. One-dimensional simulations with exact QED rates and realistic plasma parameters validate these predictions. The discharges generate pair multiplicities up to $M_\pm \sim 10^4$ and excite electric field oscillations with spectra consistent with pulsar radio microstructure. These results provide a theoretical framework connecting microphysical gap dynamics to macroscopic observables.

We extend the finite-solid-angle general relativistic radiation transport method of C. J. White et al. (2023) to time-dependent spacetimes represented in ADM form. This Valencia-type solver retains the angular transport and local implicit matter coupling of the original HARM-type solver, but replaces its time-independent Kerr--Schild tetrad and conserved-variable normalization with an Eulerian formulation. A Cholesky-gauge spatial tetrad makes the frame and its derivatives algebraic functions of the ADM variables, providing smooth, metric-compatible angular transport. The resulting transport system couples directly to an evolving spacetime, agnostic to the gauge evolution equations. Our test suite, including flat and curved beams, radiation--fluid coupling, and time-dependent geometries, establishes the accuracy and robustness of this approach. We further apply the Valencia-type solver to a radiative circumbinary disk, illustrating its potential for multi-messenger studies of dynamical strongly gravitating systems.

Coherent radio emission is observed from compact astrophysical objects with relatively weak magnetic fields, including millisecond pulsars and white dwarfs, the latter being proposed as possible sources of long-period radio transients. In such environments, the standard pair discharge mechanism---driven by curvature radiation and one-photon pair production---can fail because the low magnetic field strength suppresses photon conversion. We analyze a discharge mechanism that operates efficiently in weak-field magnetospheres, including two-vertex quantum electrodynamic processes: inverse Compton up-scattering of background photons followed by either two-photon or one-photon pair creation depending on the seed photon temperature. Using first-principles radiative particle-in-cell simulations incorporating exact QED cross sections, we demonstrate that these mechanisms robustly generate pair cascades in millisecond-pulsar magnetospheres and in hot white-dwarf environments. The resulting system exhibits limit-cycle behavior and generates electromagnetic field fluctuations capable of producing coherent radio emission, providing a natural explanation for radio activity in low-field compact objects.

We have discovered PSR J2108+5055, an extremely luminous but sporadic mode-changing rotating radio transient (RRAT), with a period of 0.495 s using the Canadian Hydrogen Intensity Mapping Experiment/Fast Radio Burst instrument (CHIME/FRB). We show that the brightest pulse from PSR J2108+5055 has a flux density of 3.1+/-1.0 kJy, corresponding to a spectral luminosity of (7.5+/-2.3)x10^23 erg s^-1 Hz^-1, assuming a dispersion-measure-derived distance of 1.6+/-0.3 kpc. We place an upper limit on the duty cycle of PSR J2108+5055 at 0.002% and measure a surface magnetic field of 5.8x10^11 G, a characteristic age of 1.2x10^7 yr, and a spindown luminosity of 2.2x10^32 erg s^-1. Using a simple model based on the Green Bank North Celestial Cap (GBNCC) survey, we place an upper limit on the number of PSR J2108+5055-like sources with similar peak flux densities in the GBNCC survey area of ~80 RRATs. We show that if PSR J2108+5055 were placed at the edge of the Local Group of galaxies, the Five-Hundred-Meter Aperture Spherical Telescope (FAST) would detect its brightest pulse. The second brightest pulse has a peak flux density of 1.5+/-0.7 kJy, and FAST would detect such a pulse out to ~1 Mpc, covering the inner Local Group, including Andromeda.

Investigating the correlation of flux variability in blazars across multiple spectral bands provides a key tool for constraining emission mechanisms and jet physical parameters. We study the gamma-ray and optical variability correlation of BL Lacertae on timescales of about 1 day during September 2022, when the source was within the TESS field of view, and over a longer period (April 2022 - September 2023) encompassing its gamma-ray flare, which finishes the series of flares during the high-activity phase. Our analysis confirms the Synchrotron Self-Compton mechanism as the origin of the gamma-ray emission, characterized by a zero time lag. For the longer interval, the Discrete Correlation Function (DCF) reveals a second statistically significant peak at the time lag of about 12 days. We demonstrate that this peak arises due to the presence of an additional flare in one of the bands, which accompanies a gamma-ray and optical flares correlated at zero time lag. We interpret the orphan flare origin in terms of the propagation of an injected blob of high-energy electrons along a jet with a decaying magnetic field, accounting for electron radiative cooling.

The constancy of Newton's gravitational constant G is a fundamental prediction underlying general relativity and a critical assumption in theories of gravity beyond it. We report a high-precision test of a possible temporal variation of G in a strong gravitational field, using high-resolution ultraviolet spectra of Ni V absorption lines in the white dwarf G191-B2B obtained with the Hubble Space Telescope Imaging Spectrograph (HST/STIS). By comparing the measured line centroids with laboratory wavelengths and isolating the gravitational-redshift contribution, we obtain dG/G = (-0.014 +/- 0.016) x 10^-15 yr^-1 at a strong-field potential phi approximately 10^4, corresponding to an absorption redshift z_abs approximately 8.47 x 10^-5. The result is consistent with a constant G and places a stringent constraint on its secular variation in the strong-field regime. Our measurement demonstrates the potential of white-dwarf stars as a sensitive probe of temporal variations in the gravitational coupling.

A black hole need not ring down in isolation, since a nearby companion can subject it to an external gravitational tide. We calculate how a quadrupole tide modifies the Schwarzschild black hole resonances. Linearising the exact tidally distorted Schwarzschild solution in the tidal amplitude $A$, we derive the diagonal odd- and even-parity perturbation equations on the deformed background and compute the formal first order displacements of analytically continued Schwarzschild resonances. Each diagonal first order shift factorises as $δω_{n\ell m}=A\,c_{\ell m}κ_{n\ell}$, giving one reduced complex coefficient for each $(n,\ell)$, expressed as a ratio of contour integrals, multiplied by a universal Zeeman-like pattern that splits the $2\ell+1$ azimuthal multiplet. For the $\ell=2$ and $\ell=3$ sectors analysed explicitly, the odd- and even-parity shifts coincide, so Schwarzschild isospectrality survives at first order in the tidal amplitude. Quadratic tidal forces, by contrast, can break this degeneracy. Moreover, for a physical companion, the astrophysically dominant $(n,\ell,m)=(0,2,2)$ mode oscillates faster and decays more slowly. Finally, we show that the eikonal shifts admit a geometric description in terms of the Penrose limit about the tidally deformed photon ring.

We study how discrete self-similarity (DSS) in the critical behavior of scalar-field collapse is imprinted on primordial-black-hole (PBH) mass functions. Using the DSS-modulated critical scaling law found in cosmological simulations, we propagate the near-threshold mass map into normalized PBH mass functions during a {kination} era. We compare Gaussian window function, $k$-space top-hat window function, and real-space top-hat window function, together with a real-space top-hat window function multiplied by a kination transfer function. We find that critical behavior in gravitational collapse produces an irreducible minimum width even for an infinitesimally narrow primordial spectrum. DSS then modulates this critical-scaling profile, generating approximately log-periodic features in mass. At fixed horizon mass, successive equal-phase points of the DSS-modulated critical mass map satisfy $Δ\ln M_{\rm PBH}=γP_{\rm ln}$. Consequently, in the narrow-spectrum limit, the corresponding structures in the final mass function are expected to satisfy $Δ\ln m\simeqγP_{\rm ln}$, or $m_{n+1}/m_n\simeq5.6$, for the fiducial Choptuik DSS parameters $γ$ and $P_{\rm ln}$. For broad primordial spectra, the convolution over horizon masses dephases the DSS pattern and progressively washes out the critical substructure. We normalize the mass functions so that we may primarily study the profile shape and the survival of DSS substructure, rather than the absolute PBH abundance. These results provide a bridge between cosmological DSS collapse simulations and PBH phenomenology including population observables.

A large suite of N-body/hydrodynamical simulations is used to demonstrate that the physical properties of the merging cluster El Gordo are well reproduced within a two-state self-interacting dark matter scenario. Our findings show that, in addition to elastic scattering, the presence of an inelastic, endothermic, up-scattering channel is essential to satisfy observational constraints derived from the measured weak lensing profiles of the two colliding clusters. We find that the observational properties of El Gordo are adequately matched by our self-interacting dark matter model within the following interval of parameters: an elastic cross-section in the range of ~ 4 -5 cm^2/gr, and an up-scattering channel bounded by an inelastic cross-section of approximately ~ 2 -4 cm^2/gr with a threshold velocity of ~1200 - 1600 kms, respectively. We argue that our conclusions depend critically on current uncertainties in the primary mass and the projected separation d_{DM}. In fact, our findings suggest that if error estimates in weak lensing measurements were significantly reduced - with future observations showing evidence of a low primary mass (<~ 10^{15} M_sun ) and a larger projected separation d_{DM} >~ 740 kpc - it would then be difficult for the proposed self-interacting scenario to be reconciled with observational constraints. We further suggest that future lensing surveys of massive, high-velocity merging clusters could be decisive in testing the proposed dark matter scenario.

Computing boson star families traditionally requires repeated solution of nonlinear eigenvalue boundary-value problems and careful numerical continuation through turning points. We develop a physics-informed neural network (PINN) that learns the map from the physical parameters and radial coordinate directly to the scalar and metric fields over an equilibrium solution manifold. Regularity and asymptotic boundary conditions are incorporated into the network output, while the training objective combines pointwise supervision, Einstein-Klein-Gordon residuals, and curve-level constraints on the Arnowitt-Deser-Misner mass and Noether charge. A trained model generates a complete configuration in a single forward pass. Across representative one-, two-, and three-branch families, the method reconstructs the mass-frequency spirals and conserved quantities, including configurations on inner branches that require delicate continuation in conventional solvers. These results establish physics-informed surrogate learning as a practical route to amortized exploration of nonlinear self-gravitating solution families.

In this work we explore the imprints of self-interacting dark matter (SIDM) on the structure of simulated galaxy groups and clusters in view of future optical surveys. We find that both baryonic and projection effects lead to a significant alleviation of the SIDM core-forming behavior on the mass and density profiles, resulting in very small ($\lesssim 5\%$) deviations from standard collisionless dark matter. The opposite trend emerges for our most massive halos, where SIDM tends to significantly enhance the central density instead; we compare those halos with the observed dark matter profiles of two galaxy clusters, MACS J1206 and Abell S1063, finding that SIDM may leave potentially detectable imprints on cluster cores when considering the small observational uncertainty of current kinematic mass measurements. Finally, we find that weak lensing observations provide a promising tool for testing SIDM on cluster scales: in an idealized scenario where systematics are under control, weak lensing shear profiles exhibit up to $\sim 20\%$ level deviations for $M_{200} \gtrsim 10^{13}\ \text{M}_\odot$ halos. Conversely, the projected concentration-mass relation is only slightly modified by our SIDM models. We also discuss the limitiations of our analysis and the impact of the simulation resolution, as well as possible extension of this work. Overall, our results provide a baseline for future SIDM studies: although line-of-sight projection and baryonic effects significantly reduce SIDM imprints on halo mass profiles, weak lensing and kinematic analyses in galaxy clusters may potentially allow for robust detection and constraining of dark matter self-interactions in massive structures from megaparsec down to kiloparsec scales.

To investigate the initial conditions of high-mass star-forming regions, we use SiO (2-1) emission to trace early shock-related kinematics toward sixteen 70 $μ$m-dark and massive clumps with luminosity-to-mass ratios ($L/M$) $< 1\,L_{\odot}/M_{\odot}$, as part of the Multiwavelength Line-Imaging Survey of the 70 $μ$m-dark and bright clouds (MIAO) project. Using ALMA observations at a spatial resolution of $\sim$0.06 pc and a velocity resolution of 0.21 km s$^{-1}$, we identify a total of thirty-seven outflows with a variety of morphologies. Outflow parameters were derived by integrating the HCO$^+$ (1-0) line wings, excluding the quiescent dense core component traced by H$^{13}$CO$^+$ (1-0). We find that outflow masses and velocities show moderate positive correlations with the masses of their driving cores. Owing to the high sensitivity of our observations, which yield longer projected outflow lengths compared to previous studies, the derived outflow dynamical ages span $\sim10^{3}$-$10^{5}$ yr. We detect six narrow-linewidth (0.6-1.4 km s$^{-1}$) and three broad ($>$ 2 km s$^{-1}$) SiO (2-1) features not associated with outflows driven by clearly identified protostars. Lacking coincident 3 mm dust continuum cores, their origins may be young outflows from undetected low-mass protostars, dissipating shocks, cloud-cloud collisions, or projection effects when the outflows lie close to the plane of the sky. The detection of these shocks and outflows in such extremely young environments demonstrates that protostellar activity has already begun.

Whether the slow solar wind originates from one coronal source or two distinct channels remains a central open question in heliophysics. Resolving this requires unsupervised separation of two populations that arrive at nearly the same bulk speed and differ mainly in heavy-ion composition. We present Solar-CDC, a self-supervised contrastive deep clustering (CDC) framework that maps plasma observables to a latent space via a Transformer encoder, optimizes a triplet margin loss, and updates pseudo-labels via $k$-means. Theoretically, we prove that neighborhood-preserving embeddings such as t-SNE and UMAP are fundamentally constrained. Preserving the neighbor graph leaves the cross-cluster cut fraction unchanged, and preserving all but a fraction $\varepsilon$ of its links moves that fraction by at most $\varepsilon$. Neither bound depends on the target dimension. A margin objective rewrites the graph and drives the cut fraction to zero. Empirically, on 30,602 Solar Orbiter observations, thirty combinations of dimensionality reduction and clustering peak at a silhouette of $0.454$, whereas Solar-CDC reaches $0.869$. Escaping the geometric bound alone does not guarantee physical validity: TriMap also optimizes triplets and reaches $0.824$, yet its clusters score below chance against the published composition taxonomy. Solar-CDC instead recovers clusters with mean charge-state ratios of $0.080$, $0.160$, and $0.400$, placing the intermediate population inside the window associated with coronal-hole boundaries. Even when the defining charge-state ratio is withheld from the inputs entirely, the model still recovers the taxonomy defined on it. Solar-CDC thus connects self-supervised representation learning to coronal source diagnostics. Importantly, a learning loss recovers physical populations only when driven by dynamically updated physically-aware clusters rather than distances.

We formulate a data-completeness test for extracting low-energy characteristic-cone running from flat-space on-shell renormalization-group residues. In four-dimensional, parity-even Einstein--scalar--Maxwell effective field theory through four derivatives and four external fields, Wilson directions are first placed on the physical EFT quotient and background propagation is represented by a traceless response on the full massless root sector. The response is identifiable from chosen amplitude coordinates precisely when the amplitude kernel lies in the response kernel. For the published opposite-helicity vector--scalar residue we find $β_μC_{γφ}^{(2)}=-55/(96π^2)$ and, after an order-reduced frame translation, the contribution $β_μ(r_T-r_γ)=-55/(48π^2M_{\rm P}^4)$. A finite operator registry gives explicit rank-two incompleteness tests: independent $F^4$ directions split photon polarizations on a magnetic background, while $\mathcal CFF$ produces an analytic splitting along a principal Weyl axis on a Petrov-I Einstein--scalar background. For the isolated scalar--photon contact, direct Schur reduction finds nonzero raw mixing but no first-order physical off-diagonal entry, by the Maxwell Ward identity. Thus the residue fixes one diagonal cone contribution but does not determine the term-complete characteristic response over the declared admissible coefficient domain.

We present a multi-sector $TESS$ photometric and spectral energy distribution analysis of the eclipsing binary CPD--82~291 (RX~J0853.1--8244). Eight $TESS$ sectors reveal well-defined eclipses and substantial, changing out-of-eclipse modulation. The asymmetries are reproduced by different surface-brightness configurations at different epochs, consistent with strong and evolving stellar activity, although the fitted circular regions are not unique maps of individual starspots. A detached-binary light-curve model yields an orbital inclination of $i\simeq82.1^\circ$ and a photometric mass ratio of $q_{\rm phot}\simeq0.464$. Without a spectroscopic radial-velocity orbit, the mass ratio and absolute parameters are model-dependent rather than dynamical measurements. Combining the light-curve geometry with the SED radius scale and \textit{Gaia} distance gives $R_1\simeq1.25\,R_\odot$ and $R_2\simeq3.70\,R_\odot$; the corresponding model-inferred masses remain substantially less secure than the dimensionless light-curve parameters. The stellar photospheres reproduce the observed SED from the optical region through WISE W4, with no statistically significant mid-infrared excess. The only positive long-wavelength deviation is a low-significance $60\,μ$m measurement, while the $90\,μ$m result is an upper limit. A cool circumbinary-dust model can reproduce this tentative signal, but such a component is not required by the photometry, and its inferred mass and radial extent are non-unique and strongly model dependent. Evolutionary tracks place the primary close to the zero-age main sequence and the secondary well above the main-sequence locus. However, the absence of radial velocities and spectroscopic youth indicators, together with $Gaia$ astrometry inconsistent with Chamaeleon~I membership, prevents a secure pre-main-sequence classification.

Recent DESI DR2 observations have renewed interest in extensions of the $Λ$CDM cosmological model, particularly through indications of a time-varying dark energy equation of state. In this work, we investigate whether such deviations may also involve interactions within the dark sector. We consider an interacting dark energy scenario in which the dark matter density evolves as $ρ_{\rm dm}\propto a^{-3+δ}$, with the constant $δ$ quantifying the interaction strength, and allow the dark energy equation of state to be either constant but different from $-1$, or dynamically evolving through the CPL parametrization. The models are constrained using Planck CMB data, DESI DR2 BAO measurements, and three Type Ia supernova compilations: PantheonPlus, Union3, and DES-Dovekie. For the constant equation-of-state case, the inclusion of DESI and supernova data leads to a preference for a small negative interaction parameter, with a significance above $2σ$. When dynamical dark energy is allowed, the evidence for interaction becomes weak, while the data favor a quintessence-like evolving dark energy component. In both scenarios, Bayesian model comparison still favors $Λ$CDM. Our results show that the inferred role of dark-sector interactions depends strongly on the nature of dark energy, highlighting the importance of jointly testing dark energy dynamics and interactions in the DESI era.

In 1980, the Universe was made of stars, cosmology was the province of less than 100 astronomers, the Hubble constant was only known to within a factor of two, and the hot big bang was the ``the standard model of cosmology.'' Particle physics was a thriving enterprise concerned with the inner space of quarks, leptons and the strong, weak and electromagnetic interactions. The Standard Model was newly established and the aspirations were for a ``grand unification'' of the forces and particles. By 2000, the agendas of inner space and outer space were inextricably linked, and $Λ$CDM with its inflation, particle dark matter and dark energy -- and a Hubble constant reliably known to better than 10\% -- was the new standard model. The big questions connecting inner space and outer space included the origin of ordinary matter, the identity of dark matter, the nature of dark energy, and an understanding of the origin of space, time and the Universe. Particle dark matter, the idea that the bulk of the mysterious dark matter is a new, long-lived or stable elementary particle, played a central in bringing together inner space and outer space, and today is still a hot topic in both fields.