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The PyLMT transient detection pipeline has been operational since November 2023, detecting transient and variable objects in the ILMT images in almost real time. Using the image subtraction technique, nearly 3700 CCD frames have been analyzed by the automated pipeline, generating nearly 23,000 alerts for the detection of verified transient candidates and cataloged variable sources. Around 21,000 of the alerts correspond to known MPC asteroids, nearly 2000 correspond to variable stars (including eclipsing binaries, RR Lyrae, Delta Scuti, T-Tauri, etc.), 509 correspond to variable AGNs (including QSOs, Seyfert galaxies, and blazars), 21 supernova candidates, and several other interesting candidates. We provide a concise overview of the detections and their significance, emphasizing the surveys potential contributions to a broad class of astrophysical and scientific cases. A transient detection dashboard called DART was developed using Streamlit to visualize and categorize candidates based on PyLMT and SIMBAD classifications. It includes cone-search functionality and displays key metadata, offering an intuitive interface that is publicly accessible. Our results demonstrate the viability of liquid mirror telescopes such as the ILMT for time-domain astronomy, emphasizing the important role that small-field survey facilities can play in systematic transient science programs.

HD 49798 is an X-ray binary consisting of a hot helium-rich subdwarf primary and an accreting compact companion with an orbital period of 1.55 d. TESS observations of its optical light curve suggest short-period brightenings superimposed on a sinusoidal variation. The latter can be attributed to the tidal deformation of the primary, while frequency analysis of the additional variations shows up to eleven frequencies which form an harmonic series based on a period of 1.4 d, in excellent agreement with the stellar rotation period inferred independently from spectroscopy. These brightenings may be explained by a slowly changing and inhomogeneous temperature distribution across the surface of the hot subdwarf, such as might be associated with a magnetic field or with the presence of Rossby waves in the stellar envelope.

Relativistic jets are observed in both stellar-mass black hole X-ray binaries (BHXRBs) and active galactic nuclei (AGNs), yet their bulk Lorentz factors differ systematically---those in black hole X-ray binaries are typically below $\sim2$, whereas AGN jets can reach $\sim50$. The origin of this discrepancy remains unclear. Searching the literature, we compile a sample of 333 AGNs with well-measured jet component motions, consisting of 270 quasars, 47 BL Lac objects, 10 FR I, and 6 FR II galaxies. We find that quasars/FR\,IIs exhibit minimal bulk Lorentz factors ranging from $\sim$1.0 to 41.5, with a mean of 11.5 (median 9.5). In contrast, BL Lac objects/FR\,Is show $Γ_{\rm jet}\sim$1.0--21.9, averaging 4.2 (median 1.5). These values, particularly the median, closely resemble those of BHXRBs, implying a strong correlation between jet speed and accretion mode. The Lorentz factor of a magnetically driven jet is mainly determined by the ratio of the magnetic pressure to rest mass energy density at the jet base. In BL Lacs/FRIs/BHXRBs, the field is maintained by the advection-dominated accretion flow (ADAF), and the gas at the ADAF surface is magnetically driven into the jets. In quasars/FRIIs, the field is maintained by the disc, while the jet base is connected to the corona. Our model calculations show that the disc field is always much stronger than that of the ADAF, and therefore leads to a larger $Γ_{\rm jet}$, which can explain the systematic difference in $Γ_{\rm jet}$ between these two types of sources.

We study the dynamics of a radiating relativistic star in the presence of the electromagnetic field and the cosmological constant. The evolution of the model originates from an initially static configuration. The temporal behaviour of the system is governed by a nonlinear second order equation which is studied using a phase plane analysis. We show that in the general case, with all physical parameters present, fold bifurcations arise which are related to nonzero charge and cosmological constant. Our treatment clarifies earlier results and we extend our study to the general solution space. We obtain a more comprehensive understanding of the temporal evolution for a shear-free configuration during collapse.

Ultralight bosons could trigger superradiant instabilities in rapidly spinning black holes, forming oscillating clouds while extracting rotational energy. We consider an extended, superradiance-informed spin distribution model that characterizes possible environment-induced spin variations and compare its predictions with the observed population of merging black hole binaries in the Gravitational-Wave Transient Catalogs (GWTCs). We find that the mass-spin relation predicted by a scalar boson with mass $m_b\sim 10^{-12} \,\rm eV$ is consistent with the GWTCs, with increasing significance from GWTC-3.0 to 5.0. The Bayes factor reaches $\ln B \approx 7.8$ for GWTC-5.0. Intriguingly, this mass range largely coincides with a previous study based on a waveform analysis of the GW190728 gravitational wave event. Our findings provide compelling evidence that a superradiance-informed spin distribution model is highly compatible with the expanding binary black hole population dataset.

Pinned superfluid vortices transmit a Magnus force to the neutron-star crust. A non-axisymmetric component of the superfluid-lattice lag can therefore support a persistent mass quadrupole. We calculate the l=m=2 response of self-gravitating, radially stratified spherical stars with SLy4 and BSk21 backgrounds, using a local microscopic pinning cap and a density-dependent Coulomb-lattice shear modulus. For a 1.4 M_sun star at 100 Hz, the equilibrium-compression maxima are epsilon=2.67x10^-9 (SLy4) and 2.44x10^-9 (BSk21). The global quadrupole is strikingly insensitive to the shear prescription: replacing mu=0.01P by the Coulomb profile and strongly varying uncertain edge layers changes the result only at the percent level. The dominant internal sensitivity is instead compressional. A density-resolved compressional kernel increases through the inner crust and steepens close to the crust-core interface, particularly for BSk21, showing that the deep inner crust controls the EoS dependence of the mountain. A fixed-composition calculation is used only as a non-relaxed sensitivity diagnostic, not as the secular prediction. At a common true local velocity benchmark, our fiducial ellipticities remain more than an order of magnitude below the complementary two-component cylindrical calculation of Gangwar & Jones (2026). We argue that the comparison points to the relative superfluid-lattice degree of freedom as the natural next ingredient for a common spherical model. The main result is therefore physical rather than numerical: the Magnus-mountain scale is robust to shear microphysics, while the deep-crust compressional response sets the leading uncertainty of the one-displacement model.

Supermassive binary black holes embedded in gas-rich environments are promising multi-messenger sources for pulsar timing arrays and future space-borne gravitational-wave interferometers. Their electromagnetic emission is governed by nonlinear plasma dynamics around the binary and is expected to inherit variability associated with the orbital motion thereof. Because active galactic nuclei are intrinsically stochastic, identifying robust binary signatures requires predictive models that connect large-scale circumbinary flows to the black holes. Previous relativistic simulations of accreting binaries have mostly focused on smaller separations and lower spins. We perform three-dimensional general relativistic magnetohydrodynamic simulations of a relaxed, magnetized circumbinary disk accreting onto an equal-mass binary black hole with a separation of $30$ gravitational radii and dimensionless spin $χ=0.9$. At these separations, the mini-disks around each black hole are persistent mass reservoirs but still show pronounced amplitude modulations governed by the eccentric circumbinary disk and the sloshing gas between the mini-disks. We analyze how the magnetic flux is transported from the circumbinary disk to the horizons, launching powerful dual jets with energy extraction efficiencies reaching $\approx 40\%$. The horizon-threading flux and jet luminosity alternate between the two black holes, producing an on-off dual-jet state. The wide jet funnels interact above the binary and form a persistent current sheet favorable to reconnection. We explore the influence of mini-disk thermodynamics, comparing efficient and inefficient cooling inside the cavity. Hotter mini-disks are less massive, exhibit weaker coherent periodicity, and launch less luminous jets despite comparable horizon-threading magnetic flux.

The search for electromagnetic signals from supermassive black hole (SMBH) binary systems is one of the cornerstones of multi-messenger astrophysics, complementing gravitational wave observations of such systems by pulsar timing arrays and LISA. Although extensive simulations have been run to understand the time variability of the bolometric luminosity from accreting binary SMBH systems, comparatively few spectral predictions have been made, and none that go beyond simple emission models. In this paper, we post-process a \texttt{HARM3D} simulation snapshot of a binary at $20 M$ separation accreting at 0.01 Eddington. For black hole masses $10^6$, $10^7$, and $10^8\, M_\odot$, we self-consistently solve for the radiated spectrum on the basis of time-steady radiation transfer, thermal balance, and ionization equilibrium, including all relevant relativistic effects as well as emission and absorption processes. Although most of the bolometric luminosity is radiated thermally by the disk, the low density regions evacuated by the binary's quadrupole moment produce copious X-rays, with $\sim40\%$ of the observed luminosity in a soft X-ray power law ($Γ= 2.3$). We identify two modes of observed azimuthal variation. The X-ray continuum varies by $\sim10\%$ due to an underlying asymmetry in the gas temperature of spiral shocks in the disk. The Fe~K$α$ equivalent width dips by $\sim25\%$ when the line of sight to the inner disk is partially obscured by the lump. These two effects share the same period and are $\sim π/2$ out of phase; the period is order days to weeks for typical AGN masses and a 20$M$ separation.

The Laser Interferometer Space Antenna is expected to observe gravitational waves from massive black hole binaries across cosmic time. Many are anticipated to be detectable hours to weeks before coalescence. We present a fast algorithm for the premerger detection and preliminary characterization of such binaries. The method performs a search for excess power with a chirping time-frequency morphology in short-time Fourier transform spectrograms. By tiling the time-frequency plane with slices defined by the quadrupole frequency evolution, we define a signal significance relative to a fitted background distribution of instrumental noise and Galactic foreground. Individual search triggers are followed by a coherence tracker that groups triggers consistent with the same physical signal over time. Doing so, our analysis provides progressively refined estimates of the chirp mass and coalescence time. We validate our algorithm on the SangriaHM LISA Data Challenge dataset, successfully detecting all 15 injected massive black hole binaries; 14 of them hours to weeks before merger, while one is only detected after the binary coalescence. The algorithm yields chirp mass relative errors below 3% for high-SNR sources and coalescence time uncertainties of up to a few hours. With a computational cost of less than a second to process a 10-day data segment on a single core, our approach is suitable for generating real-time alerts, triggering protected observational periods, and providing informative priors for Bayesian parameter estimation.

Globular clusters are efficient factories of recycled pulsars, but searches toward high-dispersion-measure (DM) clusters can be strongly limited near 1 GHz by dispersive smearing and interstellar scattering. We present the first MeerKAT S-band (nu ~ 2.4 GHz) pulsar survey of 14 globular clusters. High time- and frequency-resolution observations were searched using segmented acceleration and jerk techniques, followed by candidate folding and targeted folding with available timing ephemerides. We re-detected 39 known pulsars and discovered four new millisecond pulsars in Glimpse-C01: J1848-0129C, D, E, and F. Multi-epoch follow-up enabled preliminary Keplerian orbital fits for J1848-0129C and J1848-0129D. J1848-0129C is an eclipsing MSP in a ~5 d orbit, placing it among long-period eclipsing systems known as huntsman binaries, while J1848-0129D is in a ~3.4 d nearly circular orbit with a massive white-dwarf companion of about 1 solar mass. Two Glimpse-C01 pulsars show large DM offsets from the cluster average. Comparison with other Galactic globular clusters indicates that intracluster DM spreads tend to increase with foreground DM, implying that narrow DM search windows may be sub-optimal for high-DM clusters. From detections and non-detections, we infer a practical single-epoch MeerKAT S-band tied-array detectability scale of about 10-20 microJy. These results demonstrate the value of high-frequency searches for pulsars in strongly dispersed and scattered cluster environments.

Inflationary magnetogenesis provides a promising mechanism for generating primordial large-scale magnetic fields, but faces challenges. In this paper, we extend the Ratra model to a non-minimal $f(R)$ gravity framework, appearing in the Lagrangian in the form $f^2(η) F_{μν}F^{μν}$, to break the conformal invariance of the standard electromagnetic action. Focusing on the post-inflationary reheating epoch, we derive analytic expressions for the magnetic and electric energy density spectra by constructing a broken-power-law evolution for the scale factor and the coupling function across the inflation-to-reheating transition. Three key theoretical constraints are imposed on the model parameter space: the strong coupling condition, the backreaction constraint, and the CMB isotropy requirement. Through numerical calculations, we obtain predictions for the present-day magnetic field strength $B_0$ and coherence length $L_{c0}$ for various combinations of the inflationary energy scale $H_f$ and the reheating temperature $T_r$. We further incorporate the nonlinear effects of magnetohydrodynamic (MHD) turbulence after reheating, including the inverse transfer process, which significantly enhances the coherence length (up to $0.1$ Mpc) while reducing the field strength by several orders of magnitude. By comparing with observational constraints from radio observations and Fermi-LAT gamma-ray data, we demonstrate that the inflationary energy scale $H_f$, the reheating temperature $T_r$, the parameter $β$, and the e-folds numbers $N_f$, $N_r$ must satisfy stringent joint constraints. This work provides a viable theoretical framework for inflationary magnetogenesis that simultaneously satisfies theoretical consistency conditions and current observational bounds.

The minimalist approach for linear stability analysis is applied to fluids and magnetized ideal plasmas in cylindrical geometry. In this approach, the dispersion relation is obtained by integrating a single first-order differential equation - referred to as the principal equation - subject to appropriate boundary conditions. We first derive the principal equation for a general unperturbed state with radially varying density and pressure, axial and azimuthal components of both the velocity and magnetic field, and a radially directed gravitational field. We then use this formulation to analyze rotating flows with axial magnetic fields, addressing both wall-bounded and interface-driven axisymmetric instabilities. In addition to exact results for selected unperturbed states, we obtain approximate dispersion relations using the WKBJ method in the incompressible and compressible limits. The analysis encompasses centrifugal, magnetorotational, and buoyancy-driven instabilities as special cases, and it clarifies how compressibility modifies their stability properties.

Low-power extragalactic jets are known to be decelerated and dissipate large amounts of energy within their host galaxies. However, the exact process by which this occurs is still elusive. The aim of this work is to probe the role of stars as triggers of jet mass-loading, deceleration and dissipation in Fanaroff-Riley type I radio galaxies. This is motivated by a theoretical model that proposes that stars interacting with the jet boundaries could facilitate entrainment of interstellar medium (ISM) gas into jets, favouring mixing and dissipation. We have performed a numerical experiment of stars entering a relativistic flow, using a relativistic hydrodynamics code. Our setup is limited to the interaction of three stars with the jet boundary, in order to assess the results in a limited, controlled, environment, although this number of stars may be plausible in the inner kpc-region of a massive galaxy. Our results allow us to estimate the amount of entrained ISM gas as the stars enter the jet. We show that the entrainment temporally induced on scales of tens of parsecs and thousands of years by evolved stars is comparable to the initial jet mass rate. The way in which this entrainment happens is by the creation of a low pressure region behind the stellar objects, which drags ambient gas into the jet flow. Our results confirm that stars interacting with the jet boundaries, and acting as catalysts of ISM/shear gas entrainment, can significantly contribute to jet mass-load and deceleration.

Long-term visual and CCD V-band monitoring of the heavily reddened Wolf-Rayet star WR 80 from 2017-2026 reveals optical fading events that depart from its long-term stable baseline. On 26 April 2017 (JD 2457870), I discovered a deep minimum using a 22-inch (0.56-m) telescope, with the source plunging from a baseline of magnitude 14.6 down to magnitude 15.8. This 6-day event was subsequently verified via archival ASAS-SN V-band records. In July 2018, my visual observations identified a short duration fade to magnitude 15.4 that went undetected in concurrent electronic V band data streams, indicating a masking effect likely caused by near-infrared red leak contamination in the CCD filters. Following a stable phase recorded by continuous CCD V-band tracking from 2023 through early 2026, a mid-2026 visual detection caught a full 16-day fading event reaching a minimum magnitude of 15.3. These combined datasets establish that WR 80 undergoes highly variable optical obscuration events.

To overcome the failure of the conventional non-relativistic description of statistics in strong gravitational fields, we develop a covariant theory for a photon gas in curved spacetime, starting from the Boltzmann equation and employing the relaxation time approximation. The transport coefficients are computed up to second order, which are not a massless limit of the massive-particle results due to the fundamentally different phase-space geometry of null particles. At second order, the gravitational field renders the coefficients tensor-valued and induces transverse fluxes, analogous to the Hall effect. Using the first-order results, we derive relativistic generalizations of Fick's and Fourier's laws and obtain the radiation diffusion equation for spherically symmetric accretion disks. This provides a covariant description of radiative transport in strong gravitational fields for high-energy astrophysical applications.

The ionisation balance in molecular clouds is regulated by several ionising sources, including cosmic rays, X-rays, and ultraviolet radiation. Their relative importance depends on the local physical conditions and on the shielding column density. We compute the contribution of the large-scale diffuse X-ray radiation field to the ionisation in molecular clouds in the absence of strong local X-ray sources, such as young stars. Our goal is to quantify its significance relative to the Galactic cosmic rays. Using measurements of diffuse X-ray emission from the first eROSITA all-sky survey, we estimate the depth-dependent X-ray ionisation rate in molecular clouds across different Galactic environments. We consider both the observed diffuse field and a deabsorbed field obtained by correcting for foreground Galactic attenuation using HI4PI line-of-sight column densities in a pixel-by-pixel framework. Diffuse Galactic X-rays are unlikely to dominate the ionisation balance in well-shielded molecular gas ($N_{\mathrm{H}} > 5 \times 10^{21} \mathrm{cm^{-2}}$), where cosmic rays remain the primary ionising agent. At low column densities, the deabsorbed diffuse X-ray field produces ionisation rate of $ζ_X \sim 10^{-18}\mathrm{s^{-1}}$ at $N_{\mathrm H} \sim 10^{19}\mathrm{cm^{-2}}$, remaining below the lower end of Galactic cosmic ray ionisation rate ($\sim 10^{-17} \mathrm{s^{-1}}$). The X-ray contribution decreases rapidly with increasing shielding, falling to $ζ_{X}\sim10^{-19}\mathrm{s^{-1}}$ by $N_{\rm H}\sim10^{21}\mathrm{cm^{-2}}$ and to $ζ_X \sim5\times10^{-21}\mathrm{s^{-1}}$ by $N_{\rm H}\sim10^{22}\mathrm{cm^{-2}}$. Diffuse X-ray may therefore contribute to the thermal and chemical structure of low-extinction material and should be considered when interpreting ionisation tracers in diffuse or cloud-envelope environments.

For fifty years the Blandford--Znajek mechanism has been a mechanism and not an exact solution: force-free electrodynamics on a prescribed metric, with the jet's own field carrying no weight. Here that field gravitates. A split monopole weighs as much as a magnetic monopole, so its self-gravity is the magnetic Reissner--Nordström geometry; two copies glued across an equatorial current sheet put hole, disk and jet-driving flux into one spacetime, and force-free plasma makes a magnetosphere of it. Three things then follow that no test-field calculation can see. First, a steady jet is impossible. A stationary horizon cannot be heated but a slipping magnetosphere necessarily heats it, so the only stationary state is a dead one corotating with the hole, and a working jet is a black hole in decay at rates the field equations fix rather than assume. Second, flux enters the laws of black-hole mechanics as a charge, sharing one extremality budget with spin. That budget caps the jet power at $c^5/48G$ whatever the mass. Third, the lifetime output is finite: a maximally spinning hole delivers $1-e^{1/4}/\sqrt2=9.2\%$ of its mass and grows its horizon area by exactly $\sqrt e$. The horizon's own moment of inertia vanishes with the irrational exponent $(\sqrt{17}-1)/2$ set by the near-horizon throat, and what is left is a rotating hole whose angular momentum has passed to its own field.

Black holes of primordial or astrophysical origin immersed in axion dark matter provide a natural laboratory for exploring the interplay between compact objects and ultralight scalar fields. While previous studies have primarily focused on superradiance and horizon-scale phenomena, the gravitational response of the surrounding axion distribution has received comparatively little attention. We investigate the dynamics of particles orbiting Schwarzschild and Kerr primordial black holes embedded in scalar-field dark matter halos. Using first-order perturbation theory, we show that the ambient halo redistributes the gravitationally bound axion cloud, shifting the characteristic radius of the gravitational atom. Numerical integrations of timelike geodesics demonstrate that the maximum orbital response consistently occurs at this perturbed radius, establishing a direct correspondence between the microscopic structure of the axion wavefunction and the macroscopic dynamics of orbiting particles. Our results identify a new purely gravitational signature of scalar-field dark matter around primordial black holes and provide a framework for probing mixed axion--primordial black hole dark matter scenarios.

The late-time ringdown dynamics of near-extremal black holes (BHs) are expected to be dominated by zero-damped modes (ZDMs), whose decay rates are parametrically suppressed relative to those of ordinary quasinormal modes. In this paper, we demonstrate that exact WKB methods provide an exceptionally powerful framework for analyzing the ZDM spectrum of near-extremal Reissner--Nordström (RN) BHs. Focusing on massless, neutral scalar modes propagating on an RN background, we present the full Stokes geometry derived from the radial eigenvalue problem and establish the corresponding exact quantization condition (EQC). Our analytic computation of the Voros symbols entering the EQC achieves higher-order accuracy for the ZDM spectrum compared to previous studies and is systematically improvable. Ergo, this work serves as a proof of concept for investigations of ZDM spectra of other systems using exact WKB methods.

In this work, we build on Ref.~[Phys.~Rev.~D 112, 124060 (2025)], where we derived the dynamics of an electrically charged binary system at second post-Newtonian (2PN) order, by extending the analysis, at the same PN accuracy, to the associated emission of electromagnetic and gravitational radiation. We focus on non-spinning binaries that evolve quasi-adiabatically along a sequence of circular orbits, and compute the 2PN expression for the corresponding total energy flux at infinity. With respect to the well-known case of a neutral binary, the presence of charge induces both a new leading-order electromagnetic contribution of dipolar nature and additional charge-dependent corrections in the gravitational sector. To account for this richer phenomenology, we extend both the PN-matched multipolar post-Minkowskian and the effective field theory approaches to the radiation sector of charged binaries, with exact agreement for the contributions computed independently in both formalisms. We derive the radiative symmetric-trace-free multipole moments of the vector and gravitational fields at 2PN order. In doing so, we also compute 2PN-accurate charge-dependent corrections to the spherical multipoles of the waveform emitted by the binary, including a new memory contribution sourced by the stress-energy tensor of the electromagnetic radiation. These results lay the foundation for developing accurate waveform models capable of assessing the observational signatures of electric charge in gravitational-wave signals.

We investigate the impact of a dark matter density spike surrounding the Milky Way's supermassive black hole (SMBH) on the detectability of Singlino-dominated neutralino dark matter within the Next-to-Minimal Supersymmetric Standard Model (NMSSM). Similar density enhancements, or mini-spikes, around stellar-mass black holes (sBHs), have also been considered. Such a dark matter (DM) candidate typically produces weak indirect detection signals in conventional dark matter halos. Additionally, a Singlino-like lightest supersymmetric particle (LSP) is very difficult to probe at the LHC or through the direct DM search experiments. On top of that, recent observation of the LUX-ZEPLIN 248 keV Nuclear-Recoil Event may hint towards a DM that can be accommodated by a Singlino with mass more than 200 GeV. Keeping these in consideration, we examine the prospects for detecting these sub-TeV dark matter scenarios through gamma-ray observations of the regions surrounding the SMBH Sgr A$^\ast$ and the sBH in the low-mass X-ray binary XTE J1118+480.

We present a dedicated search for monochromatic gamma-ray emission from a recently proposed nearby dark matter subhalo candidate. Using nearly 15 years of Fermi-LAT Pass 8 data, we perform a sliding-window search for gamma-ray lines between 10 and 300 GeV. We do not find any statistically significant evidence for a line signal. The largest excess occurs at $E_γ\simeq 28 \, {\rm GeV}$ with a local significance of $2.5σ$. We therefore derive 95% confidence level upper limits on the annihilation cross section for $χχ\rightarrow γγ$. Under the assumed NFW subhalo model, the resulting constraints are stronger than existing Galactic Center line limits over much of the explored mass range. We further translate these line constraints into bounds on well-motivated WIMP models, such as Higgs-portal and Wino dark matter scenarios, restricting previously open parameter regions consistent with thermal freeze-out as well as models associated with dark matter interpretations of the Galactic Center Excess.

We present simultaneous XRISM, XMM-Newton, and NuSTAR observations of ESP 39607, a Seyfert 2 galaxy at $z = 0.201$. XRISM/Resolve reveals two absorption features near 4.7 and 4.9 keV in the observed frame, consistent with redshifted Fe XXV He-$α$/Fe XXVI Ly-$α$ absorption from gas inflowing at $v_{\rm in} \simeq 0.16c$. The high velocity identifies the absorber as an ultra-fast inflow (UFI), which is detected at $\sim 3$-$3.7σ$ across different methods and continuum models. Photoionization modeling yields $\log ξ/{\rm erg\,s^{-1}\,cm} \simeq 3.7$-$3.8$ and a column density $\log N_{\rm H,abs}/{\rm cm^{-2}} \simeq 23.2$-$23.8$, the latter depending on the assumed metallicity. The inflow velocity and line properties are consistent with those reported from two earlier NuSTAR epochs, indicating that similar inflowing material was present over a baseline of at least 2.2 yr in the source rest frame. Across all three epochs, the combined detection significance of the UFI is $5.3σ$. Given the dynamical timescale of a few days at the inferred radius, $R \simeq 49$-$77\,R_{\rm g}$, the multi-year evidence favors a scenario in which the inflow is continuously replenished, forming an accretion "cascade", rather than a single long-lived cloud. With an estimated mass inflow rate of $\dot{M}_{\rm in} \simeq 0.3$-$1.4\,M_\odot$ yr$^{-1}$, depending on metallicity, and a ratio $\dot{M}_{\rm in}/\dot{M}_{\rm acc} \simeq 0.2$-$1.0$, the inflow could supply a substantial fraction of the accretion needed to power the central active galactic nucleus.

Numerical relativity (NR) simulations provide the most faithful representation of the gravitational waves (GWs) emitted by binary black hole (BBH) systems during merger. In the context of GW astronomy, tasks such as parameter estimation can require vast numbers of waveform evaluations per second across the entire parameter space. Since performing full NR simulations for each evaluation is not computationally feasible, interpolating methods for existing NR waveforms, known as surrogate models, have been developed with marked success. In this paper, we build on our previous work to introduce methods to train a fast surrogate model based on neural networks in order to generate BBH merger waveforms, including the fundamental (2,2) mode, as well as the (3,3), (2,1), (4,4), (3,2), (4,3) and (5,5) higher-order modes. Applying a pretraining step on approximant data before fine-tuning on NR data allows us to smooth out the parameter space, and making use of the parallelization ability of GPUs to project the NR waveforms in the inclination-phase $(ι, φ)$ sphere during training allows the fitting of all the explored modes simultaneously. The developed surrogate model, \texttt{DANSur\_HM}, achieves average mismatches of the order of $10^{-4}$, with the worst mismatch at $2.5\times10^{-3}$, and achieves throughput above $6\times10^5$ waveforms/second on an NVIDIA V100 GPU. Parameter estimation tests confirm the usefulness of the inclusion of higher modes.

The Pulsar Monitoring in Argentina (PuMA) collaboration systematically monitors southern glitching pulsars, maintaining high-cadence single-pulse records of the Vela pulsar. We present a pulse-per-pulse reanalysis of the 2024 major glitch of Vela (PSR~J0835$-$4510) with the 400~MHz-bandwidth ROACH backend of the Argentine Institute of Radioastronomy, and extend our machine-learning single-pulse pipeline---Isolation Forest outlier rejection, $β$-Variational-AutoEncoder denoising, and Self-Organizing-Map clustering---to new observations of PSR~J1644$-$4559 and the millisecond pulsar PSR~J0437$-$4715. For Vela, the 4- and 6-cluster decompositions of the eight days bracketing the glitch reproduce, with seven times the previous bandwidth, the behavior found with the narrow-band ETTUS receivers: higher-amplitude clusters peak earlier in phase, are narrower, more skewed, and less populated. With the glitch jump and its two exponential recovery terms included in the timing solution, the mean profile is stable to 1\% across all eight days (width change $-0.5\pm0.9$\% from pre- to post-glitch); omitting the recovery terms would mimic a post-glitch broadening of up to 55\% through a folding-frequency error at the $10^{-7}$ level. The clusters of PSR~J1644$-$4559 differ almost exclusively in amplitude, as expected for a scattering-dominated profile. For PSR~J0437$-$4715, retaining the 10\% of pulses with the highest peak-dominance score doubles the signal-to-noise ratio, and a five-cluster decomposition yields narrow, phase-ordered groups a factor $3.6\pm0.4$ narrower than the average profile, suggesting a $\sim$3.5-fold improvement in cluster-based timing precision for this pulsar-timing-array target, to be confirmed in a follow-up paper.

Recent baryon acoustic oscillation measurements from DESI Data Release 2, when combined with CMB and supernova data, strengthen the motivation for exploring departures from $Λ$CDM in the late-time expansion history. Because an evolving dark-energy equation of state and an interaction within the dark sector can produce partially degenerate effects on the background expansion, their observational signatures should be assessed simultaneously. We first consider an interacting $w_0w_a$CDM model with $Q=βHρ_{\rm de}$, using Planck and ACT CMB data, DESI DR2, and DES-Dovekie supernovae. Allowing the dark-energy equation of state to evolve substantially weakens the preference for a nonzero coupling, while the preference for dynamical dark energy persists. The interaction provides essentially no additional improvement in the best fit, suggesting that part of the coupling preference found in more restricted interacting models may reflect a degeneracy with dark-energy dynamics. We then examine the same interaction for three one-parameter dynamical dark-energy trajectories: thawing, mirage, and generalized emergent dark energy (GEDE). The role of the interaction depends strongly on the assumed trajectory. The thawing and GEDE models favor sizable couplings of opposite signs, whereas the mirage trajectory already closely follows the dark-energy evolution preferred by the data and provides little support for an additional interaction. These models also predict markedly different signatures in structure growth, ranging from enhanced matter clustering in the interacting thawing model to strong suppression in interacting GEDE. These contrasting growth signatures, despite substantial degeneracies at the background level, highlight late-time large-scale-structure observations as a promising avenue for distinguishing dark-energy dynamics from dark-sector interactions.

The thickness of a reconnecting solar wind current sheet is normally inferred from a single spacecraft as the product of the boundary-normal speed and the crossing duration. Multipoint measurements have tested this method for generic solar wind current sheets and constrained the geometry of reconnection exhausts, but a direct comparison with single-spacecraft thickness estimates for the same reconnection-associated crossings is still lacking. We analyze four current-sheet crossings observed by Magnetospheric Multiscale in the pristine solar wind on 2017 November 10 the two boundaries of a confirmed reconnection exhaust and two nearby current sheets. The tetrahedron separation was $\approx 16$ km. Cross-correlation of the magnetic-field ramps gives millisecond-level lag uncertainties, boundary normals to $4^\circ-8^\circ$ and speeds to $5\%-8\%$, while single-threshold timing at these separations is noise dominated. The exhaust edges are 29-31 ion inertial lengths ($d_i$) thick. The two edge normals differ by $22^\circ$ (68% interval [$19^\circ,26^\circ$]), resolving a nonparallel exhaust geometry. At the exhaust edges, the measured boundary speeds agree with three standard single-spacecraft estimates to 4%-15% and remain within about one Alfvén speed of the plasma motion. Estimating the normal from one spacecraft is the larger source of error, though the thickness is still recovered to within tens of percent when a degenerate minimum-variance solution is rejected. At the actively reconnecting sheet, the boundary speed exceeds the local plasma speed along the normal by $29\% \pm 10\%$.

The masses of Galactic pulsars in binaries measured through radio timing point to structure in the mass distribution with implications for dense matter and astrophysical formation processes: a bimodal shape with peaks at ${\sim} 1.3\,M_\odot$ and ${\sim} 1.6\,M_\odot$, with a cutoff above ${\sim}2\,M_\odot$. However, this observed population of radio pulsars is shaped not only by intrinsic pulsar properties, such as birth masses, binary evolutionary pathways and dense-matter constraints, but also by observational effects. In existing catalogs of pulsar mass measurements, observational selection effects influence (i) which systems are detected in the first place (detectability) and (ii) which systems yield well-measured masses (measurability). In this work, we revisit the radio pulsar population distribution in the context of observational effects associated with pulsar radio timing. Simulating systems of radio pulsars and timing observations, we track the process by which a given system ends up in an observational dataset and estimate the impact of the binary and pulsar parameters. We fold this selection function into hierarchical population inference and extract the intrinsic astrophysical distribution of pulsars observed with radio timing. We jointly infer the populations of pulsar mass, companion mass, orbital eccentricity, orbital period and pulsar spin period. Selection effects have minimal impact on the mass distributions, but more significantly affect other parameters. The ratio of circular-to-eccentric systems shifts from an observed $1\!:\!1$ to an astrophysical, selection-corrected $2\!:\!1$ ratio, while the true population is shifted toward longer orbital and spin periods than observed.

We present the results of directed searches for continuous gravitational waves from unknown neutron stars in five Milky Way globular clusters. We carry out these searches in the LIGO data from the first eight months of the fourth LIGO-Virgo-KAGRA observing run using the WEAVE semicoherent program, which sums matched-filter detection-statistic values over many time segments spanning the observation period. No gravitational wave signal is detected in the search band of 20--475 Hz. Injections of simulated continuous wave signals in the data indicate that we achieve the most sensitive results to date across most of the explored parameter space volume, obtaining median 95% confidence level upper limits as low as <inline-formula><mml:math><mml:mo>~</mml:mo><mml:mn>4.2</mml:mn><mml:mo>×</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mo>-</mml:mo><mml:mn>26</mml:mn></mml:mrow></mml:msup></mml:math></inline-formula> near 282 Hz for NGC 6397. We also derive upper limits on neutron star ellipticity and <inline-formula><mml:math><mml:mi>r</mml:mi></mml:math></inline-formula>-mode amplitudes, reaching <inline-formula><mml:math><mml:mo>≲</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mo>-</mml:mo><mml:mn>5</mml:mn></mml:mrow></mml:msup></mml:math></inline-formula> and <inline-formula><mml:math><mml:mo>≲</mml:mo><mml:msup><mml:mn>10</mml:mn><mml:mrow><mml:mo>-</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:msup></mml:math></inline-formula>, respectively, at frequencies above 200 Hz.

We investigate whether hairy black holes generated through spontaneous symmetry breaking in Einstein-Scalar-Gauss-Bonnet (ESGB) theory, involving a complex scalar field with a global $U(1)$ symmetry, can be compatible with cosmological evolution. To this end, we introduce the ESGB theory with a scalar self-interaction that becomes relevant on cosmological scales while remaining negligible near the black hole. Owing to the time dependence of the GB term on cosmological scales, the scalar field dynamics in the evolving FLRW background differ qualitatively from those in the nearly static black hole background. In particular, for scalar-GB couplings compatible with hairy black hole formation, the effective potential supports a symmetry-broken vacuum throughout inflation. However, after inflation, a decelerated expansion changes the sign of the GB term, temporarily making the effective potential unbounded from below. As the GB contribution subsequently decreases, the scalar self-interaction eventually dominates and restores the symmetry. Within this schematic framework, we derive stringent constraints on the coupling strengths, the cutoff scale, and the black hole mass, which primarily arise for avoiding efficient tachyonic amplification of the scalar field perturbations during the unbounded phase. For cutoff scales compatible with both cosmological evolution and scalar hair formation, we find that only ultralight black holes with masses of the order of a few grams can develop scalar hair, identifying them as hairy primordial black holes.

The solar tachocline, a thin shear layer separating the differentially rotating convective zone (CZ) from the underlying rigidly rotating radiative zone (RZ), remains a dynamical mystery. Under the influence of "radiative spreading" (the process by which meridional circulation, baroclinicity, and differential rotation burrow through a stably stratified fluid), the tachocline should have spread significantly by the current age of the Sun. Some unknown torque must therefore rigidify the whole solar interior below the CZ and keep the tachocline confined to a thin layer. At the same time, the spin-down process (through which cool stars shed angular momentum via surface magnetic torques) must extract angular momentum from the solar RZ, presenting a second mystery: solar spin-down must be communicated from the near-surface layers to the deep interior, all the while leaving the tachocline intact. In this work, we explicitly analyze the dynamics of radiative spreading in two 3D, spherical-shell, fully nonlinear fluid simulations of a solar-like CZ--RZ system, one without a magnetic field (hydrodynamic---HD) and one with a small random seed magnetic field (magnetohydrodynamic---MHD). We find that radiative spreading is unmitigated in the HD case (as expected), but in the MHD case, a self-excited dynamo not only confines the tachocline, but \textit{also} extracts angular momentum from the RZ, thereby communicating the spin-down downward. We thus speculate that solar and stellar tachoclines may be intimately linked to both the spin-down process and global dynamo.

Recently, we constructed analytical purely electric and purely magnetic black-hole solutions in Einstein--Euler--Heisenberg theory, while the corresponding dyonic solutions were obtained numerically \cite{Luo:2026srx}. Motivated by the recent analytical construction of a dyonic black hole at the special coupling locus $b=a/2$ \cite{Ahmed:2026ufj}, we revisit the general dyonic sector. We show that exact analytical dyonic black-hole solutions can be constructed for nonlinear couplings satisfying $2b>a$, without imposing the restriction $b=a/2$. The mass function is expressed in closed form in terms of the Lauricella hypergeometric function. In particular, our construction yields an exact dyonic solution for the Euler--Heisenberg coupling $b=7a/4$. The solution of Ref.~\cite{Ahmed:2026ufj} is recovered in the limiting case $2b\rightarrow a$.

Topological defects are ubiquitous in physics, arising from condensed matter physics to the early universe. Although there exist many universal scaling laws for correlations between topological defects, such as Porod scaling, the fingerprint of topological defect cores has remained largely unexplored. Here, we discover a universal scaling law in the region $k>1/ξ$, where $ξ$ is the healing length of the topological defects, taking the scaling of the form factor $S_f \propto k^{-(d+p+2)}$, where $d$ is the spatial dimension and $p$ is the defect codimension. We analytically prove that this exponent originates from a universal V-shaped cusp at the defect core and is independent of the underlying system and dynamics. Numerical simulations verify this scaling law in four typical frameworks: the time-dependent Ginzburg-Landau and Gross-Pitaevskii equations in the weak-coupling regime, the gauge/gravity duality model in the strong-coupling regime, and the Klein-Gordon equation in the Friedmann-Robertson-Walker background in cosmology. Our work provides a new probe for studying topological defects in systems ranging from superconductors to cosmological phase transitions.

This volume defines the exoplanet science program enabled by the dedicated high-contrast coronagraph in the baseline science payload of the 3.5-meter Segmented-Mirror Robotic Space Telescope. The observatory architecture incorporates the optical interfaces, wavefront sensing and control, pointing stability, and operations software required for coronagraphic observations from the outset. The observing strategy gives priority to the nearest stellar systems because they provide the most accessible laboratories for planetary exploration and the most likely destinations of future interstellar missions. The diffraction limit sets a reflected-light horizon of roughly 10--15 pc for planets at 1 AU and roughly 50--80 pc for Jupiter analogs. Within those horizons, the telescope can image nearby giant planets, obtain reflected-light spectra of their atmospheres, survey young systems and circumstellar disks, and support the habitability and biosignature programs that larger future missions will pursue. The wide-field imager complements the coronagraph through transit photometry, occurrence-rate statistics, and long-term monitoring of stellar magnetic activity. A systematic census of the nearest stellar neighbors provides a lasting reference for exoplanet science and future space exploration.

The LUX-ZEPLIN (LZ) Collaboration recently reported one event consistent with a $248$ keV nuclear recoil in a $2.84$ tonne-year exposure, with a maximum local significance of $3.4σ$ and a global significance of $2.6σ$. We investigate whether the dark matter (DM)--nucleon interactions favored by this high-energy event can arise from particle DM models that simultaneously reproduce the observed relic abundance and satisfy indirect-detection constraints. Using the published LZ efficiency and operator significances, we show that elastic spin-independent (SI) scattering poorly explains an isolated high-energy recoil because its spectrum is concentrated at lower energies, whereas elastic spin-dependent (SD) $\mathcal{O}_4$ scattering remains viable. Endothermic scattering instead naturally suppresses the low-energy rate and shifts the recoil spectrum toward the observed energy. A thermal pseudo-Dirac fermion with an off-diagonal vector interaction provides a simple realization of this mechanism. For $m_χ\simeq1$ TeV, the relic-density requirement predicts $σ_N\simeq6.5\times10^{-43}\,\mathrm{cm}^2$, while a splitting $δ\simeq297$ keV shifts the recoil spectrum into the LZ event region. Present-day indirect-detection signals can be strongly suppressed because freeze-out proceeds mainly through coannihilation, while the excited state is depleted at late times. A thermal Higgsino provides a more predictive realization: its relic abundance fixes the mass near $1.1$ TeV, while a splitting $δ\simeq 371$ keV is required to reproduce the event. This interpretation is testable through the associated gamma-ray line signal. Overall, combining direct detection, relic density, and indirect detection significantly restricts the viable interpretations of the LZ event and provides concrete targets for future searches.

KIC~8462852 (Boyajian's star) shows deep, asymmetric, and highly irregular dimming events with no simple repetition pattern. A symmetric 1.1\% transit detected by \emph{TESS} in 2019 has been interpreted as a possible giant planet or brown dwarf, while the irregular dips are generally attributed to transiting dust from exocomets or planetesimal fragments. We test whether the broader dip families may nevertheless recur orbitally. Our scenario assumes a major disruption that produced fragments with slightly different periods, causing successive returns to spread progressively in orbital phase. We compare this recurrent model with a null hypothesis of chronologically independent family centers, accounting for the observing window, and marginalize over the recurrence period $P$ and dispersion scale $σ_P$. We obtain $B_{10}=44.9$ in favor of recurrence, corresponding to ``very strong'' evidence on the Jeffreys scale. The maximum-likelihood solution is $P_{\rm ML}=781.6$~d and $σ_{P,\rm ML}=80.0$~d, close to the 776.1-d timescale obtained if D800 and the 2019 \emph{TESS} event are separated by four revolutions. Independently of the timing fit, this period predicts a transit duration of about 20.5~h for the published stellar and transit parameters, in close agreement with the observed $\sim21$~h. The result is conditional on the adopted topology, priors, family definition, and observing selection function, and does not prove orbital recurrence. Nevertheless, the family timings strongly favor this specific recurrent-fragment model over independent occurrence, making progressive orbital phase dispersion a viable and physically motivated interpretation.

Higgsino dark matter remains one of the most convincing dark matter candidates. It can exist in a ``quasi-Dirac" regime, when the splitting between two Majorana components is on the order of $O(\rm few~\,MeV)$ or less. Owing to the strong gravitational pull of the Sun, the DM particles accelerate to up to $\sim 1400$\,km/sec in the solar core, which allows for inelastic scattering on heavy elements and very effective capture onto solar-bound trajectories. We evaluate the expected flux of the neutrinos from the expected $χχ\to W^+W^-,ZZ$ annihilation for the cosmologically preferred mass, $m_χ\simeq 1.08$\,TeV while keeping the mass splitting $δ$ as a free parameter. Confronting it with the non-observation of high-energy neutrinos from the Sun by the IceCube experiment, we obtain a robust limit, $δ>566$\,keV. These limits exclude the interpretation of the recent LZ event in terms of endothermic inelastic scattering of Higgsino dark matter on xenon nuclei.

We show that a single dark-photon dark matter framework can simultaneously account for two recently reported anomalies: the halo-like Galactic gamma-ray excess identified by Totani in 15 years of Fermi-LAT data, and the $E_{\rm nr}=248\pm23\,({\rm stat})\pm23\,({\rm sys})$ keV nuclear-recoil event of interest reported by the LUX-ZEPLIN Collaboration. The dark matter is a $U(1)_X$ dark photon $X$ with mass $m_X=420$ GeV, stabilized by a dark parity that forbids kinetic mixing with the Standard Model photon. A light scalar mediator $φ$, already required to explain the Totani excess via Sommerfeld enhancement, is extended to couple a nearly degenerate heavier vector partner $V$ to $X$. The resulting inelastic transition $X+N \to V+N$, with mass splitting $δ\simeq316$~keV close to the kinematic endpoint for $m_X=420$ GeV, naturally reproduces the localized LZ event once the detector energy resolution is included, while leaving the relic abundance and the halo phenomenology of the original Totani-motivated benchmark essentially unchanged.

We propose quasicrystalline inflation. Six quasiperiodic phases decompose into three phonons and three phasons. It turns out that a coherent pure-phason displacement can generate a local power dipole while the linear traceless quadrupole vanishes. From spatially varying quadratic effective field theory, we derive off-diagonal correlations whose momentum transfer is restricted to integer combinations of the six icosahedral wavevectors. These correlated off-diagonal signals provide a characteristic observational signature of primordial quasiperiodic order, primordial diffraction.

Fast and accurate stellar evolution emulators---surrogate models that approximate expensive simulation outputs with machine learning (ML)---are powerful tools for modern stellar characterization, hierarchical inference, and population synthesis. We analyze the grid density required for reliable emulation by training ML algorithms on main-sequence models with masses M=[0.7,1.2] solar masses. This range is challenging to emulate due to rapidly varying evolutionary behavior caused by the radiative-to-convective core transition, as well as the requirement to match the part-per-thousand seismic precision that has been delivered for such stars from the NASA Kepler mission. Generating grids from analytical models, as well as MESA, YREC, MIST, and ASTEC, we compare linear interpolation, k-nearest neighbors, random forests, and neural networks (NNs) in interpolating the stellar observables: T_eff, L, Delta nu, and nu_max. While NNs outperform other methods, sparse grids induce localized failures in the core-transition region, resulting in unstable derivatives, ensemble disagreement, and fragmented posterior distributions during inference. Performance gains from denser grids are non-uniform, suggesting that adaptive grid generation should be favored over uniform refinement. Finally, we show that NN ensembles allow for localized uncertainty propagation, more accurately reflecting emulator reliability across parameter space than global uncertainty estimates. As we consider only the two-dimensional case of varying only stellar mass and age along the main sequence, these results represent a lower bound on the challenge in emulating stellar evolution simulations for precision asteroseismology.

Extreme-mass-ratio inspirals (EMRIs) provide a unique laboratory for probing strong-field gravity and complex relativistic dynamics. We study a tidally deformed EMRI composed of a stellar-mass secondary orbiting a supermassive (non-)rotating black hole embedded in an external, adiabatically varying tidal environment. These systems provide a restricted, yet astrophysically motivated, realization of the relativistic three-body problem, expected to appear in active galactic nuclei, with a clear hierarchy of masses and radiation-reaction timescales. The external tidal deformation breaks the axisymmetry of the Kerr spacetime, rendering the geodesic dynamics non-integrable and giving rise to chaotic motion. The resulting signature of non-integrability is characterized through Poincaré maps and rotation curves constructed from the ratios of the fundamental frequencies of bound radial, polar, and azimuthal motion. We identify two prominent plateaus whose widths increase with the tidal field amplitude, signaling a transition from weak to strong chaos. We then demonstrate the sensitivity of the chaotic dynamics to the orientation of the orbit relative to the tidal field. We further analyze the proper-time evolution of the action-angle variables, showing that the angle combinations associated with the dominant commensurabilities are phase locked, thereby allowing the associated tidal contributions to induce secular changes in the constants of motion, whereas off-plateau angle combinations circulate. These results clarify the dynamical significance of the prominent plateaus and provide a novel phase-space characterization of tidal resonances in EMRIs. Finally, we discuss the potential role of radiation-reaction effects in driving EMRIs through tidal island crossings and the implications for gravitational-wave inference with future detectors.

We develop a canonical ADM framework for gravitational backreaction during inflation. Our approach extends the formalism used to compute cosmological correlators by applying it to the evolution of the quantum background, which we identify with the metric one-point function. The aim is to assess the quantum stability of inflationary geometries under gravitational backreaction. Within this framework, the backreaction is determined by the expectation values of the Hamiltonian constraint and the equations of motion for the spatial metric. Working in the exact de Sitter limit, we apply the framework to a massless minimally coupled spectator scalar field and the physical graviton polarizations. At one loop, their backreaction renormalizes the relation between the cosmological constant and the Hubble parameter without inducing any secular departure from de Sitter evolution, in agreement with previous results. We perform the calculation using a hard momentum cutoff and show that a fixed physical cutoff allows the homogeneous background equations to be renormalized with time- and background-independent coefficients, in contrast to a fixed comoving cutoff. Finally, we demonstrate that the explicit representation of the backreaction depends on the gauge condition imposed on the metric fluctuations, as well as on the background-fluctuation split. Nevertheless, these different representations are related by a gauge transformation and are therefore physically equivalent.

We compute the excitation factors of Kerr-de Sitter black hole quasinormal modes using two different techniques: a Heun function representation and an expansion of the solution in terms of hypergeometric functions. Exceptional points at which the complex frequencies of different overtones coincide are a generic feature of the Kerr-de Sitter quasinormal mode spectrum. Near exceptional points, the modes exhibit a "hysteresis phenomenon" that was previously found for Kerr black holes perturbed by massive fields and the absolute value of the excitation factors of the individual modes is significantly enhanced, while they acquire nearly opposite phases. We extrapolate the excitation factors to small values of the cosmological constant and find good agreement with previous calculations in the Kerr limit.

The phase coherence of primordial perturbations shapes the acoustic peaks of the CMB and is regarded as a key signature of inflation. Inflationary scenarios at different energy scales, thus with different durations, are commonly expected to leave different levels of coherence. We show this expectation fails: because the curvature perturbation is conserved on super-Hubble scales, the coherence at recombination inherits a value fixed by the observed primordial spectrum alone. This holds irrespective of the inflationary energy scale and the subsequent expansion history.

White dwarf--brown dwarf (WD--BD) binaries are intrinsically rare systems that provide a unique opportunity to study binary evolution and the formation of substellar companions. Despite recent observational progress, only a small number are known in the solar neighbourhood. We investigate whether their scarcity can be explained by binary formation and evolution together with observational selection effects. We extend the MRBIN binary population synthesis code into the substellar regime by incorporating brown dwarf evolutionary models and an extended initial mass function. We simulate the stellar population within 100 pc of the Sun and compare the predicted WD--BD population with the observed sample. Our simulations predict 13+-5 WD--BD systems within 100 pc, consistent with observations. These systems represent only 0.1% of the local white dwarf population, confirming their rarity. The models reproduce the overall distributions of white dwarf masses, temperatures, and orbital periods, although the simulated brown dwarfs are systematically hotter than observed. Close WD--BD binaries are underproduced with the standard common-envelope efficiency 0.3, suggesting that higher efficiencies may be required to reproduce the observed short-period systems. The simulations also reproduce the observed deficit of systems at intermediate orbital periods between post-common-envelope binaries and wide non-interacting systems, as well as a weakened brown dwarf desert in main-sequence--brown dwarf binaries.

We study scalar perturbations of a seven-dimensional Kerr--AdS black hole with three independent rotation parameters. In this geometry, the Klein--Gordon equation separates into one radial and two angular second-order linear ordinary differential equations, each with five regular singular points. We apply the Hill determinant method to compute analytic expansions of the accessory parameters in two different parameter regimes. The resulting accessory parameter expansions coincide with those obtained from the instanton part of the Nekrasov--Shatashvili function of four-dimensional $\mathcal{N}=2$ quiver gauge theories. These expansions are then used to derive perturbative expressions for the angular eigenvalues in the slowly rotating limit and for the quasinormal mode frequencies in the small black hole limit.

Primordial black hole (PBH) calculations usually treat rare curvature peaks as isolated collapsing regions. Using fully nonlinear $3+1$ numerical-relativity simulations in a radiation-dominated Universe, we demonstrate that neighbouring primordial curvature perturbations need not map one-to-one onto PBHs: they may ultimately disperse, collapse collectively into a single PBH, or undergo distinct local collapses and form more than one PBH. In the family of two-component profiles studied here, the latter outcome is a pair of PBHs, identified by the coexistence of two disconnected apparent horizons on at least one time slice. We introduce a nonspherical quasi-local compaction diagnostic based on the Hawking mass and referenced to a round flat-FLRW sphere of equal area. It retains the angular structure of the curvature field and reduces to the standard Misner-Sharp compaction function in spherical symmetry. The global maximum of this diagnostic, $\mathcal K_{\rm form}$, provides an empirical indicator of whether at least one PBH forms, with a transition near $\mathcal K_{\rm form,c}\approx0.56$ and modest profile-dependent scatter. For forming bimodal profiles, we supplement the nonlinear compactness with a signed linear surface strength evaluated on the same probing spheres. The viability of the weaker local branch and the competition between the local and common-enclosing branches improve the empirical discrimination between single- and double-PBH outcomes. Our results therefore show that the maximum curvature amplitude alone does not determine the collapse outcome, which also depends on the spatial extent, characteristic scales, and geometry of the surrounding curvature environment.

We show that Gravity from Entropy (GfE) exhibits a tensor-propagation pathology on generic FLRW backgrounds. In vacuum, in the symmetry-inheriting single-multiplet sector, and for the algebraic perfect-fluid constitutive embedding, the strict-principal TT system has a nonzero real characteristic only when \(\dot H=K/a^2\). Away from this locus the temporal principal roots become complex, signaling a high-frequency hyperbolicity obstruction. Under the stated isotropy assumptions, a rank theorem further shows that one foundational multiplet cannot provide the isotropic bivector response needed to remove this problem.

Spatially resolved stellar kinematics are critical to the high precision achieved by cosmological probes utilizing time delays of strongly lensed quasars. Combined with high-resolution imaging and lens modeling, dynamical models of the 2D resolved kinematics of the deflector galaxy tightly constrain the mass profile and break the mass-sheet degeneracy, in turn providing tight constraints on the Hubble constant when the time delays are included. We extract stellar kinematics of the deflector galaxies in the quadruply lensed quasar systems HE0435-1223, PG1115+080, and WFI2033-4723 from James Webb Space Telescope Near-Infrared Spectrograph (JWST-NIRSpec) integral field spectroscopy. The kinematic maps reach average per-bin total (statistical and systematic) uncertainties of 6-11%, with average bin-to-bin correlated errors of only $\sim 1.2\%$. The aperture-integrated velocity dispersions are statistically consistent with the values used in the previous TDCOSMO analysis (all within $0.9σ$), with their average uncertainty reduced from 3.7% to 2.4% owing to improvements in the data reduction and kinematic-extraction methodology. We classify PG1115+080 as a fast rotator, HE0435-1223 and WFI2033-4723 as slow rotators within the probed radii, and we refine the source redshifts from the kinematics of the lensed host galaxies. Kinematic maps will be combined with time delays, lens models, and line-of-sight convergence estimates to measure cosmological parameters in the upcoming TDCOSMO 2026 milestone publication.

We study the linear onset of matter-induced scalarization for a static black hole surrounded by two spatially separated thin matter shells. We assume that the conformal matter coupling is unity on the scalar-free background and that its logarithmic derivative vanishes there. The scalar perturbation then decouples from the metric and matter perturbations at first order, while the invariant surface traces of the shells give singular terms in the scalar equation. For a static spherical black-hole exterior with no bulk scalar effective-mass term between the shells, the onset reduces to the finite-rank condition $$ 1-a_1-a_2+(1-χ)a_1a_2=0, \qquad χ=\frac{{\cal S}(R_2)}{{\cal S}(R_1)}, $$ where $a_j$ is the attractive strength of shell $j$ normalized by its one--shell threshold on the same background and ${\cal S}$ is the static radial resistance. This relation shows that two individually subcritical shells can collectively destabilize the scalar-free black hole. We derive the critical scalar cloud in closed form and verify numerically, in the Schwarzschild probe problem, that a growing mode with a finite growth rate appears beyond the threshold. For an exact scalar-free background consisting of three Schwarzschild regions joined by two Israel shells, we separately derive the static onset condition and the corresponding critical cloud. The exact Israel trace also exhibits a sign transition whose light-shell limit occurs at the Schwarzschild photon sphere.

The bispectrum of cosmological perturbations is an important probe of inflation and the underlying particle physics. However, calculating it becomes challenging in inflation models where inflaton dynamics is dominated by quantum diffusion rather than slow-roll, especially in the multi-field case. In this paper, employing the stochastic-$δ\mathcal{N}$ formalism, we propose a Monte Carlo-based method to calculate the bispectrum in the squeezed limit, as an extension of the method for the power spectrum that we previously proposed. Our method involves generating paths of inflatons' time evolution that branch only several times, avoiding nested path generation, which incurs a prohibitive computational cost. As numerical demonstrations, we apply the proposed method to single- and double-field chaotic inflation for validation, and to hybrid inflation with mild waterfall, for which, to the best of our knowledge, the bispectrum is calculated for the first time in this work.

The South Pole is among the driest sites on Earth, and the resulting high atmospheric transparency makes it an excellent site for millimeter-wave astronomical observations. Nevertheless, for bolometric surveys of the cosmic microwave background (CMB), fluctuations in line-of-sight water vapor drive variable atmospheric emission, which has a significant impact on survey sensitivity. We have deployed a water vapor radiometer (WVR) to characterize these fluctuations in space and time and to compare atmospheric and CMB signals with other sites. This WVR has been monitoring conditions from the South Pole over the past nine years, co-located and co-observing with the BICEP series of telescopes. In this work, we analyze the performance of the WVR and the characteristics of the South Pole atmosphere and demonstrate coherent wind-driven transport of water vapor structures across the site. We show that fluctuations in CMB detector timestreams are well correlated with fluctuations in atmospheric water vapor, providing independent justification for baseline filtering procedures used to remove these fluctuations and providing a new pathway to detect and mitigate the temperature-to-polarization leakage that currently limits the precision of ground-based CMB polarization measurements.

We study the dark matter (DM) density and velocity distribution in the solar neighborhood of Milky Way-like galaxies using the TNG50-1 run of the IllustrisTNG simulation suite. Milky Way-like galaxies are selected according to both their halo mass and their bulge-to-total stellar mass ratio, and the solar-neighborhood region within each galaxy is identified from the positions and number density of stars, so that DM particles associated with the galactic disc are extracted while contributions from the halo component are suppressed. Averaging over the selected galaxies, we obtain a local DM density of $ρ\simeq 0.47\pm0.02~{\rm GeV\,cm^{-3}}$, consistent with the range inferred from observations. The disc-based extraction gives a higher peak density, $0.41\pm0.02~{\rm GeV\,cm^{-3}}$, than the value $0.34\pm0.02~{\rm GeV\,cm^{-3}}$ from a simple distance-based extraction, probably because it excludes the low-density DM in the halo. The width of the density distribution, on the other hand, is nearly unchanged. The velocity distribution is well described by an isotropic Maxwellian with a peak velocity of about $226~{\rm km~s^{-1}}$, close to the value assumed in the standard halo model. The differences in the density and velocity distributions between our disc-based and simple distance-based extractions are not so large as to significantly affect the interpretation of direct-detection experiments.

We identify a boundary-geometry-driven mechanism for the dynamical formation of marginally outer trapped surfaces (MOTSs) in vacuum general relativity. Mild three-dimensional anisotropies evolve inside a compact Cauchy domain whose effective isotropic thickness remains controlled, while the generalized boundary mean curvature can increase during either contracting or expanding boundary evolution. This drives the boundary across Yau's geometric threshold, forcing MOTS formation from initially untrapped data. We further interpret the characteristic shear construction of Ref.~\cite{MondalYau2026} as the null manifestation of the same anisotropic vacuum dynamics. The result provides a purely vacuum physical realization of MOTS formation through global geometric effects, without invoking a short-pulse concentration mechanism for gravitational radiation.

Making up a sizeable portion of the galactic census, stellar multiples are experiencing a renaissance. Enabling the study of multiple strands of the study of cool stars, stellar multiples have been found and characterised in great numbers by the missions of the last decade, allowing the exploration of stellar parameters and populations, observation of stellar interactions, studies into stellar formation and evolution, and characterisation of circumbinary systems. This exciting explosion of science is only set to continue, with future missions set to offer even further insights into the topic. Within these proceedings we will summarise the presentations and discussions on cool stellar multiplicity within our splinter sessions at the 23rd Cambridge Workshop on Cool Stars, Stellar Systems, and the Sun, as we examine the present state of the field and look to what the future may bring.

We study thermal energy fluctuations of cosmological horizons within the canonical ensemble framework, treating the horizon as a thermodynamic system characterized by temperature and entropy. The analysis is performed for a class of gravitational theories, including (n+1)-dimensional Einstein gravity, Gauss-Bonnet gravity, Lovelock gravity, and models incorporating quantum deformed entropy corrections. We find that horizon energy fluctuations stabilize to a constant value in the asymptotic de Sitter limit, independent of the underlying gravity theory and robust against higher-curvature and quantum corrections. It is worth mentioning that in its final de Sitter state, the universe obeys holographic equipartition condition and in consequence the horizon entropy attains a maximum constant value, just like an ordinary macroscopic system. These findings establish a unified thermodynamic picture in which entropy maximization, holographic equipartition, and the suppression of energy fluctuations collectively characterize the asymptotic de Sitter universe as the equilibrium end state of cosmic evolution.

Effective-source formulations provide a practical route to gravitational self-force (GSF) calculations when singular retarded fields cannot be handled directly mode by mode. Up to now, only frequency-domain first-order GSF for circular orbits in Schwarzschild spacetime was obtained with the effective-source method. We construct and implement a frequency-domain extended effective-source (EES) formulation for first-order Lorenz-gauge GSF on eccentric orbits in Schwarzschild spacetime. The central obstacle is that radial libration forces the physical puncture and effective source to switch between interior and exterior branches, limiting their differentiability and producing slow spectral convergence. We overcome this obstruction by analytically extending both branches across the libration region and solving the coupled Lorenz-gauge perturbation equations for the resulting smooth extended sources. This provides an end-to-end gravitational EES implementation for eccentric motion and validates a computational ingredient needed for extending frequency-domain effective-source calculations toward second order.

This study investigates an Einstein-nonlinear electrodynamic black hole generated by a Yukawa-screened electromagnetic potential and examines its thermal properties through the calculation of the fundamental thermodynamic potentials and variables. The effect of thermal fluctuations on the calculated standard thermodynamic quantities is analyzed through two different correction terms added to the Bekenstein-Hawking entropy. In this work, the thermodynamic behavior in cases where the black hole has a relatively large event horizon is investigated using a logarithmic correction term representing corrections arising from quantum fields in constant backgrounds. In addition, thermal fluctuations occurring in cases where the event horizon is small are analyzed through an exponential correction term added to the entropy, reflecting non-perturbative quantum effects. Finally, the thermodynamic functions for all obtained cases are examined graphically, and the stability properties of the black hole are discussed in detail.

We study the relativistic transformation of temperature for effective cosmological fluids with negative pressure within a covariant thermodynamic framework. The Lorentz transformation of temperature is derived for barotropic fluids with $p=wρ$ and for the (generalized) Chaplygin gas with $p=-A/ρ^α$. For barotropic fluids with constant negative equation-of-state parameter, we show that negative pressure suppresses the growth of temperature under relativistic boosts. In contrast, the Chaplygin gas exhibits a qualitatively different behavior due to its density-dependent pressure, leading to a monotonic increase of the transformed temperature with velocity. The dependence of the relativistic temperature on the relative velocity and background energy density is illustrated through representative examples.