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Black holes embedded in a dark matter background represent an important candidate model that extends the standard vacuum case, characterizing the strong gravitational environments at galactic centers and the gravitational influence of dark matter. This study focuses on dark matter halo-modified Kerr black holes and systematically investigates the observational characteristics of their surrounding thin accretion disks. The dark matter halo is modeled by a general double power-law density profile, whose integrated mass $M_D(r)$ modifies the radial mass function of Kerr metric to $m(r) = M + M_D(r)$. Based on this spacetime, we analyze the observational properties of their thin accretion disk, including the radiative flux, temperature, differential luminosity, and spectral luminosity as a function of radius, with respect to the black hole spin and dark matter halo parameters. Furthermore, by combining ray-tracing methods, we simulate the bolometric image of the thin accretion disk under different black hole spins, dark matter halo parameters, and viewing inclinations. The dark matter halo enhances the gravitational potential, shifting the innermost stable circular orbit (ISCO) of the accretion disk outward, suppressing the peak radiative flux, and producing a fainter image, thereby generating signatures that are possibly observational distinguishable from standard vacuum Kerr black holes.

The effective-one-body (EOB) framework, originally formulated within the post-Newtonian (PN) expansion, is central to modeling and interpreting gravitational-wave signals. Recent developments have incorporated the post-Minkowskian (PM) expansion into EOB theory. In this work, we focus on the bound state dynamics in the PM approximation up to the third order and construct the core ingredients of EOB: the effective metric. We examine two correspondence strategies, one based on the radial action variable and the other on the precession angle. We demonstrate that the radial action variable provides a consistent correspondence, which is further verified by the correspondence based on the precession angle. Building on these results, we adopt an isotropic gauge with a Schwarzschild-like parametrization to fix the remaining freedom. Within this parametrization, the effective metric coefficients are determined at 3PM order. Our results provide a consistent effective metric for the bound state dynamics.

The static tidal Love numbers (TLNs) of $4$-dimensional black holes vanish for bosonic perturbations but are generically nonzero for fermions, with rare exceptions. In this paper, we show that for static, spherically symmetric black holes, fermionic TLNs vanish if and only if the black hole is extremal, in the sense that its horizon is degenerate. This follows from a closed formula for the static fermionic TLN of any asymptotically flat black hole, obtained by solving the static massless Dirac equation exactly on an arbitrary such spacetime and imposing regularity at the horizon. As applications, we analyze the Culetu--Simpson--Visser regular black hole and the loop-quantum-gravity remnant black holes, whose extremal configurations lead to vanishing fermionic yet nonvanishing bosonic TLNs.

We present a catalog of physical parameters for powerful jet-accretion disk-black hole systems in one of the largest samples of gamma-ray emitting jetted active galactic nuclei (AGNs), including jet kinetic and radiative powers, jet radiative efficiencies, bulk Lorentz factors, black hole spins, accretion-disk magnetic fields and Compton dominance. Comparing jet kinetic power estimators for blazars, values derived from spectral energy distribution (SED) fitting tend to exceed those estimated via cavity power and other scaling relations. For radiatively efficient AGNs, most sources are inferred to possess high spins; for radiatively inefficient AGNs, many potentially have high spins, though some may differ. This indicates that black hole spin does not effectively distinguish radiatively efficient from inefficient jetted AGNs. Our results suggest accretion-disk magnetic field strength as a key discriminator, proposing a tentative dividing value of $\approx 10^{3.9}$ Gauss between radiatively efficient and inefficient populations. Jet power and bulk Lorentz factor exhibit significant correlations with black hole mass in radiatively efficient AGNs, while weak-to-moderate correlations are observed in radiatively inefficient AGNs within narrow accretion-rate bins. Our analysis reveals that jet power correlates with both disk luminosity and magnetic field strength. Furthermore, correlations linking Eddington ratio and Compton dominance with jet properties are consistent with the jet-accretion connection. Finally, jet radiative power and bulk Lorentz factor show a potential dependence on black hole spin. These results are consistent with the scenario in which jets are powered and accelerated by energy extraction from rapidly spinning black holes via accretion-disk magnetic fields.

Self-bounded dark matter (DM) subhalos are predicted to populate galactic halos in great abundance in the Cold Dark Matter (CDM) scenario. These substructures can leave observable imprints in strong gravitational lensing and have shown the ability to account for flux-ratio and position anomalies in multiply imaged systems. In this paper, we utilize the DM subhalos to address the image position anomalies of the two radio quads of HS 0810+2554 observed with the Very Long Baseline Interferometry. We model the lens using an elliptical power-law macro-lens supplemented by a population of CDM subhalos from numerical simulations and perform a dual-source reconstruction to fit all eight radio images simultaneously. We find that subhalos below $10^{6}M_\odot$ induce astrometric shifts smaller than the measurement uncertainties, whereas more massive subhalos naturally generate the required milliarcsecond perturbations without significantly altering the global lens configuration. Including CDM subhalos improves the fit from $χ^2=60.38$ for the pure macro-lens to $χ^2=1.61$. Our results show that the position anomalies of HS~0810+2554 can be explained within the CDM framework and do not by themselves necessarily require non-standard scenarios like fuzzy DM or angular complexity in the macro-lens. Instead, they provide a sharp and testable manifestation of the subhalo population predicted by CDM.

In February 2016 the LIGO and Virgo collaborations reported the discovery of gravitational waves in merging black holes, with the conclusion that their observational data did not show any violation of general relativity. The joint LIGO and Virgo team presented an upper limit on the graviton mass, using tests of modified gravitational dynamics. Yukawa-type gravitational potential corrections are often used as generic finite-range parametrisation in modified gravity contexts, including massive-gravity inspired models. Yukawa corrections are derived by semi-empirical approach, in the framework of f(R) gravity, a type of modified gravity which generalises Einsteins general relativity. Contrary to this approach, we use a classical Newtonian gravitational potential corrected by nonlinear effects in order to obtain a characteristic wavelength of the nonlinear density wave. This wavelength is then phenomenologically identified with an effective graviton Compton wavelength, leading to a model-dependent estimate of an effective graviton mass within the galaxy scale. The presented approach is independent from other methods published until now.

We investigate the temperature encoding process of two-level probes in de Sitter spacetime within the framework of open quantum systems. From a quantum-metrological perspective, we quantify the temperature encoding rate, which characterizes the precision of estimating a temperature parameter with a fixed total probe time. The maximal encoding rate is obtained by optimizing the initial state, evolution time, and measurement basis of each probe. For a static probe separated by a finite distance from a freely falling observer, both the intrinsic Gibbons--Hawking temperature and the position-dependent Unruh temperature are encoded in the probe state. We find that the encoding rate of the effective temperature is equal to the sum of the encoding rates of the intrinsic temperature and the Unruh temperature associated with the probe's inherent acceleration. Interestingly, when the intrinsic temperature is sufficiently small, the encoding rate of the intrinsic temperature initially increases with the Unruh temperature, reaches a maximum, and then decreases to zero. Thus, a nonzero inherent acceleration does not necessarily suppress the encoding of the intrinsic temperature. Instead, there exists an optimal inherent acceleration at which its encoding rate is maximized. Furthermore, we investigate the encoding rate of the Unruh temperature and the minimum total probe time required to estimate it with sufficient precision as functions of the separation distance. We find that the required total probe time and the corresponding number of probes remain experimentally feasible even when the probes are located relatively far from the cosmological horizon, with a radial position as large as $0.1$ times the horizon radius.

The effect of deflection of a light signal that propagates through the gravitational field of a solar system body at rest is considered in the case that the source and the observer are at a finite distance from the body. The observer is assumed to be located somewhere nearby the Earth, for instance at Lagrange point L2 of the Sun-Earth system, while the spatial position of the celestial light source is arbitrary. The gravitational fields in the exterior of the bodies are described by the full set of time-dependent mass-multipoles and spin-multipoles of these bodies. So the gravitating bodies can be of arbitrary shape, inner structure and rotational motion. The unit tangent vector of the light trajectory at the position of the observer is determined in the 1PN and 1.5PN approximation of the post-Newtonian (PN) scheme. A simplified expression for the unit tangent vector is obtained, where all terms are neglected that together contribute less than 10 nano-arcseconds in light deflection for all astrometric configurations between source, body and observer. It is shown that in the case of an axi-symmetric body the unit tangent vector of the light ray as well as the light deflection are given in terms of Chebyshev polynomials. This fact allows for determining the effect of light deflection in the gravitational fields of the bodies up to any order of the mass-multipoles and spin-multipoles. It is shown that the total light deflection, that is the angle of light deflection where source and observer are located at infinite spatial distance from the body, represents an upper limit of the effect of light deflection. These investigations are aiming at astrometric measurements on the sub-micro-arcsecond level of accuracy.

We study the conformal scattering of massless scalar waves in Minkowski spacetime. The conformal scattering problem is formulated as a Goursat (characteristic initial-value) problem of the physical wave equation in compactified double-null coordinates, including the neighborhood of spatial infinity $i^0$. As null infinities $\mathcal{I}^\pm$ lie on the domain boundary by construction, asymptotic radiation is directly accessible. We consider three physical scenarios: free wave propagation, scattering off a Pöschl--Teller (PT) potential, and the semi-linear $|φ|^{n-1}φ$ wave equation. For multipole numbers $\ell =0,1$, an explicit stencil, averaging along the spatial direction, yields globally second-order convergent results. For $\ell \ge 2$, an implicit stencil averaging along the temporal direction is required for numerical stability. Although the singular $i^0$ reduces the convergence of the radiation data on $\mathcal{I}^+$ to first order, Richardson extrapolation enhances the effective convergence rate to approximately $1.5$. For PT scattering, our method accurately computes scattering quantities, notably the phase shifts induced by the potential. In the semi-linear case, our method captures the physical signatures of a self-defocusing Kerr nonlinearity, including self-phase modulation and spectral broadening. The compactified double-null framework proves to be simple and efficient, suggesting a promising approach to the global evolution of conformal scattering.

Some dynamical spacetime solutions that describe ultra-compact objects are analysed. We show that by turning a static spacetime that describes a one-way wormhole into a dynamical time-dependent one, a singularity might arise in general. Several well-known wormhole solutions are studied, which are shown to become singular when promoted to a time-dependent wormhole. However, we show that one can construct a dynamical wormhole free of singularities. The corresponding Lagrangian that holds such dynamical spacetimes is also reconstructed, based on a two-scalar-field model free of ghosts. Energy conditions are also analysed, which might remain satisfied for a dynamical -singular- wormhole. Finally, the evolution of the optical appearance of such dynamical objects is simulated and compared to static solutions. Some interesting features emerge that point to a way to measure the time evolution of dynamical objects by looking at the photon ring structure around the object.

In this work, we investigate Hawking radiation and second order quantum corrected thermodynamics of a Vaidya-Bonnor black hole surrounded by quintessence. Within the Hamilton-Jacobi tunneling formalism, analytical expressions for the event horizons, tunneling probability, and Hawking temperature are derived by treating the quintessence field as a perturbative contribution. The classical thermodynamic quantities, including entropy, heat capacity, enthalpy, Helmholtz free energy, and Gibbs free energy, are then obtained and analyzed. Quantum thermal fluctuations are incorporated through logarithmic and inverse-entropy corrections to the Bekenstein-Hawking entropy, leading to second-order corrected thermodynamic quantities. Their effects on thermal stability and phase transitions are examined in detail. Furthermore, analytical expressions for the quantum-corrected remnant radius and remnant mass are derived, showing that the combined effects of quintessence and quantum corrections can prevent complete black hole evaporation and lead to the formation of a stable remnant. Our results show that both quintessence and higher-order quantum corrections enhance thermodynamdymic stability and significantly favor the formation of stable black hole remnants.

We perform a cosmographic analysis of Type Ia supernovae using the Pantheon+\&SH0ES, DES-SNY5 and Union3 compilations. We consider different redshift intervals, analyzed through a third-order Taylor expansion and a Padé $(1,2)$ approximation of the luminosity distance. First, we first infer the cosmographic parameters directly from the observed supernova redshifts. Afterwards, we extend the analysis by including a dipole correction associated with the local peculiar velocity field, constraining both its amplitude and direction. For Pantheon+\&SH0ES, the Cepheid calibration allows a direct determination of the Hubble constant, whereas for DES-SNY5 and Union3 we fix $H_0$ to set the absolute distance scale. By progressively increasing the maximum redshift of the sample, we study how the inferred cosmographic parameters depend on the adopted redshift interval. We find that the Hubble constant obtained from Pantheon+\&SH0ES remains consistent with previous determinations for both cosmographic parameterizations. Instead, the agreement of the deceleration $q_0$ and jerk $j_0$ parameters with the $Λ$CDM values depends on the adopted compilation and improves mainly for Pantheon+\&SH0ES as the redshift interval is enlarged. Moreover, the reconstructed dipole parameters remain stable across the redshift intervals considered, with velocity amplitudes of order $300\,\mathrm{km\,s^{-1}}$, for all three supernova samples. Finally, fixing the dipole parameters with the cosmic microwave background values leads to a slight shift from the fiducial $Λ$CDM values of the deceleration $q_0$ and jerk $j_0$ parameters.

We investigate a class of late-time cosmological models derived from the phenomenological framework of variable matter diffusion. In these scenarios, energy-momentum conservation requires a continuous energy exchange between matter and an effective scalar-field dark-energy component, $φ$. We consider a baseline constant-diffusion scenario alongside four non-linear power-law parametrizations, in which the diffusion coefficient evolves as a function of the scale factor, matter density, scalar-field density, or Hubble expansion rate. To assess their cosmological viability, we implement these models within \texttt{SimpleMC} and constrain them using late-time observations, including cosmic chronometers, baryon acoustic oscillation measurements, Type Ia supernovae with and without the local SH0ES calibration. In the absence of the local calibration, the diffusion models yield only modest improvements in the fit ($Δχ^2 \approx -4$), performing comparably to the CPL parametrization while exhibiting negative Bayesian log-evidence differences relative to $Λ$CDM. In contrast, including SH0ES leads to a dramatic reduction in the minimum $χ^2$ ($Δχ^2 \approx -22$) and decisive Bayesian evidence in favor of the diffusion framework ($Δ\ln\mathcal{Z} \approx 9$). Remarkably, the single-parameter constant-diffusion model accounts for virtually all the statistical improvement, outperforming the CPL parametrization by more than 10 units in $χ^2$ and more than 8 units in $Δ\ln\mathcal{Z}$. The four non-linear extensions provide only negligible additional improvements ($Δχ^2 \approx -1$), indicating that current late-time background observations favor the presence of a non-vanishing matter-diffusion interaction over $Λ$CDM, while providing no statistically significant evidence for a specific time-dependent functional form of the diffusion coefficient.

We study the quantum interference of two paths that enclose a slowly rotating, infinitely long, and infinitely thin cylindrical shell, using the spacetime metric induced by the gravitational source. We show that the rotation of the shell affects the interference pattern even though it does not contribute to the classical motion of particles propagating outside the shell. Furthermore, we find that the gravitomagnetic field is non-vanishing only in the region inside the shell, yet it contributes to the interference taking place entirely in the exterior region. This phenomenon is therefore a gravitational analogue of the Aharonov-Bohm effect, in which a field confined to an inaccessible region influences the quantum phase of particles propagating in a field-free region.

We develop a semi-analytic extension of the Web-Halo Model (WHM) to Hu-Sawicki $f(R)$ gravity, with the aim of linking nonlinear matter clustering to the successive stages of cosmic-web collapse. The cylindrical sheet and filament windows of the original WHM are replaced by axisymmetric ellipsoidal top-hat windows, yielding a modest improvement around the perturbative-to-nonlinear transition without introducing additional fitting parameters. Modified gravity is incorporated through environment-dependent chameleon spherical collapse, from which the collapse threshold and virial overdensity are obtained and propagated through the sheet, filament, and halo contributions. For $|f_{R0}|=10^{-5}$ and $10^{-6}$, the predicted nonlinear enhancement is broadly consistent with the scale-, redshift-, and field-strength dependence seen in the e-MANTIS emulator, with closer agreement for the weaker field and at higher redshift. The component responses show that sheets and filaments contribute substantially around the transition regime, while the halo response becomes increasingly important at smaller scales. As complementary diagnostics, no displacement of the BAO peak is resolved, whereas tomographic weak-lensing spectra retain a percent-level response to the modified matter power spectrum. The extended WHM therefore provides a physically interpretable framework for tracing screened modified-gravity effects across the cosmic-web collapse hierarchy.

We compiled data for 127 hosts (plus six candidates) and used them as constraints to construct interior models of the hosts using the {\small MESA} code. Two significant conclusions emerge from these models. First, except for a few stars, the hosts' metallicity ($Z_0$) is greater than 0.007. This suggests a possible suppression of the occurrence of planets below $Z_0\approx0.007$. Second, it concerns how chemical evolution unfolds in the galactic disc. For a given $Z_0$ value, considering the oldest stars, there is a linear relationship between $Z_0$ and age ($t_9$). This line is around $t_9=13.4$ Gyr at $Z_0=0$, a value consistent with the age of the Galaxy. The linear relationship continues until around $t_9=6$ Gyr, and the maximum value of $Z_0$ remains constant between $t_9=2-6$ Gyr. We further modelled 12 hosts classified as red clump (RC) stars in the literature, explicitly accounting for mass loss along the red giant branch. These models highlight the critical role of mass-loss assumptions in determining the initial masses and ages of RC hosts, and their implications for the survival and evolution of close-in planets. Another key outcome of this study is the discovery of the relationship between $Z_0$ and the observed metallicity ($Z_{\rm s}$) for the hosts. We obtain a useful expression for $Z_0$, the input parameter for the models, as a function of stellar mass, radius, and $Z_{\rm s}$. This expression can be used to estimate $Z_0$ based on the reduced surface metallicity due to microscopic diffusion. We also derive an expression for planetary mass relative to the orbital semimajor axis and host mass. This expression may indicate a mass distribution near the inner disc where these planets formed, except for hot-Jupiters. Planet radii appear to depend on the planet's mass and irradiation energy, as well as the orbital period.

JWST has enabled the measurement of carbon, oxygen, and sulfur abundances in the atmospheres of directly imaged planets. Interpretation of these abundances from a planet formation standpoint requires the corresponding abundances for the host star. In this work, we present detailed characterizations of the cold imaged planet hosts AF Lep A and $ε$ Indi A using high-resolution Gemini/GHOST spectra. We derive the atmospheric parameters $T_{\rm eff}$ and $\log{g}$ using two different approaches, revealing differences in $T_{\rm eff}$ up to $\sim260\,$K. The derived parameters are subsequently incorporated in measurement of 16 elemental abundances (C, O, Na, Mg, Si, S, K, Ca, Sc, Ti, Cr, Mn, Fe, Ni, Zn, Y) and several abundance ratios. Utilizing both the spectral fit and the equivalent width methods, we find solar C/O, C/S and O/S ratios ($<1.5σ$) for AF Lep A and $ε$ Indi A. We compare our measured abundances and their ratios with those of the planets AF Lep b and $ε$ Indi Ab, with the elevated abundances for the planets relative to their host stars strongly indicating formation by core-accretion pathways.

The key focus of this research work is the analysis of a non-singular cosmic bounce in the context of $\mathcal{F}(Q)$ gravity, with $Q$ representing the non-metricity scalar. We consider the gravitational Lagrangian $\mathcal{F}(Q)=Q+ψQ^n$ in the presence of a modified Chaplygin-type matter source with a flat Friedmann-Robertson-Walker spacetime and a perfect matter distribution. In order to proceed, we adopt two approaches: a reconstruction approach using scale-factor ansatz and analysis of a two-dimensional autonomous dynamical system. Our results imply that the geometry coupling parameter $ψ$ plays an important role and causes geometrical repulsion for violating the null energy condition. A numerical scan of the $(ρ_0,ψ)$ parameter space suggests that there is a critical energy density for the bounce to take place, below which the universe evolves towards the standard singular cosmological solution. Moreover, the effective equation of state slowly evolves towards the de Sitter value ($ω_{eff}\rightarrow -1$) and the squared sound speed is bounded by the stability and causality condition ($0\leq C_s^2\leq1$). It is found that $\mathcal{F}(Q)$ gravity provides a coherent geometric picture of the non-singular bouncing universe in accordance with the cosmic accelerated expansion.