Motivated by the growing recent interest in black hole solutions immersed in astrophysical dark matter environments, we construct an exact static, spherically symmetric black hole solution sourced by a Dehnen $\left(2,3,0\right)$ dark matter halo through the full Einstein field equations and investigate the physical consequences of the surrounding halo on the resulting spacetime geometry. The influence of the halo on optical phenomena is analyzed via null geodesics, where we show that the dark matter environment substantially modifies photon trajectories, displaces the circular photon orbits, and deforms the associated gravitational lensing structure. By evaluating the Lyapunov exponent of unstable null geodesics, we further determine the corresponding behavior of massless quasinormal modes in the eikonal regime, revealing explicit corrections to the oscillation and damping spectrum induced by the halo. We then explore the thermodynamic properties of the black hole--halo system by computing the conserved mass, Hawking temperature, entropy, heat capacity, and Gibbs free energy, allowing for a detailed assessment of both local and global thermal stability. Our analysis demonstrates that the dark matter halo increases the radius of the photon sphere and the apparent shadow, enlarges the domain of thermodynamic stability, and generates nontrivial phase structures absent in the vacuum Schwarzschild case. These results highlight that realistic dark matter environments can produce observable and thermodynamic deviations from isolated black hole geometries, potentially offering novel signatures of halo-induced gravitational effects.

We present a novel rotating black hole solution surrounded by a Hernquist dark matter halo, obtained by applying the Newman--Janis algorithm to the exact Schwarzschild--Hernquist spacetime. The resulting Kerr--Hernquist geometry provides an axisymmetric background for investigating scalar-field dynamics in realistic dark matter environments. Using the analytical asymptotic matching method, we derive the quasibound-state spectrum, identify the conditions for scalar cloud formation and the black hole bomb instability, and obtain an analytic expression for the superradiant scattering amplification factor. We show that the halo preserves the hydrogen-like structure of the quasibound-state spectrum while introducing corrections governed by the combination $\rho_0 r_0^3$. Increasing the halo density and scale radius enhances the scalar-field binding energy, lowers the critical field mass for scalar cloud formation, suppresses the growth rate of the superradiant instability for co-rotating modes ($m_\ell>0$), and accelerates the decay of counter-rotating modes ($m_\ell<0$). Furthermore, the dark matter halo reduces both the magnitude and frequency range of superradiant amplification, thereby weakening energy extraction from the black hole. These results demonstrate that the Kerr--Hernquist geometry provides a unified framework for studying quasibound states, scalar clouds, black hole bombs, and superradiant scattering, while revealing how a Hernquist dark matter halo leaves observable imprints on the spectrum and stability of rotating black holes.

A central challenge in testing inflationary scenarios with cosmic microwave background (CMB) data is to derive predictions for cosmological observables that remain accurate beyond the slow-roll regime, where the standard consistency relations are no longer applicable. We address this issue in the context of Einstein--Gauss--Bonnet (EGB) gravity by introducing a phase-$\theta$ parametrization of the inflationary dynamics. Within this framework, the background evolution and the coefficients governing scalar and tensor perturbations are expressed entirely in terms of a single monotonic phase variable and the Hubble parameter. This construction provides a closed, analytical mapping between the background parameters of a given model and the associated inflationary observables. A notable advantage of the proposed parametrization is that it remains regular throughout the inflationary epoch, including the end-of-inflation regime, in which the conventional slow-roll consistency relations no longer hold. As an illustrative application, we consider a Starobinsky-type potential supplemented by a linear coupling between the inflaton and the Gauss--Bonnet invariant. Using the proposed formalism, we demonstrate that the resulting predictions of the Starobinsky model are consistent with the most recent constraints from ACT DR6 and BICEP/Keck, explicitly incorporating the impact of the non-minimal Gauss--Bonnet coupling on the expected values of the cosmological perturbation parameters. Finally, we compute the corresponding relic stochastic gravitational-wave background and evaluate its detectability with current and forthcoming gravitational-wave observatories.

We propose a small-throat prescription for the wave function of a closed universe in the Lorentzian path integral formalism, motivated by the idea that universe creation may be obtained as the decoupling, or pinch-off, limit of a tunneling geometry connected to another universe through a small throat. Instead of retaining the parent-universe side explicitly, we describe the remaining half-geometry by a minisuperspace path integral with boundary conditions imposed at the throat. To model the finite throat, we introduce a small radiation component parametrized by $\epsilon$ in a closed minisuperspace model with a positive cosmological constant. The radiation term produces two turning points, an inner one $q_-\sim O(\epsilon)$ and an outer one $q_+\sim H^{-2}$, where $q$ is the square of the scale factor. Our prescription imposes the Neumann condition $\dot q(0)=0$ at the initial endpoint and restricts the initial size $q_i=q(0)$ to a small-throat domain $0<|q_i|<\sqrt{\epsilon}/H$ that contains $q_-$. This restriction selects the Riemann sheet containing the small-throat tunneling saddle and its Picard--Lefschetz cycle, while excluding the unsuppressed saddle associated with the outer turning point $q_+$. Taking the limit $\epsilon\to0$ after this finite-throat saddle problem has been defined, the small-throat domain collapses to $q_i \to 0$, and the saddle action reduces to that of the standard tunneling saddle. Other choices of lapse contour can instead select Hartle--Hawking-type growing branches. In this sense, the tunneling wave function can be obtained as the limiting form of tunneling from an arbitrarily small universe in a Lorentzian path integral, rather than by imposing a boundary condition directly at a vanishing geometry.

This paper investigates higher-dimensional scalar-tensor theories of gravity with nonminimal coupling, focusing on the reconstruction of exact spherically symmetric solutions. We systematically apply the formalism developed in previous works, which demonstrates that any static spherically symmetric metric can be represented as an exact solution of a scalar-tensor theory with specific coupling functions $f(\phi)$ and potential $U(\phi)$. Our analysis centers on two important classes of solutions in arbitrary spacetime dimensions: the Fisher-Janis-Newman-Winicour (FJNW) metric and its limiting case, the generalized Yilmaz-Rosen metric. We derive the key relations for the coupling function $f(\phi)$ and the scalar field potential $U(\phi)$ for both solution families using the master equation formalism in the Jordan frame. For the FJNW metric, we find that in the special case $s = 2$, $D = 6$, the coupling function $f(\phi)$ is positive in the domain $u^3 > M$, corresponding to gravitational attraction and a canonical scalar field with vanishing potential $U(\phi) = 0$. In contrast, for the generalized Yilmaz-Rosen metric in arbitrary dimensions $D > 4$, the reconstructed coupling function is always negative, $f(\phi) < 0$, indicating a phantom scalar field with negative kinetic energy and repulsive gravity.

Within Einstein power-Yang-Mills gravity (EPYM), we build a rotating black hole via the Newman-Janis procedure applied to the spherically symmetric static seed, obtaining a Kerr-like metric controlled by the spin \(a\), the magnetic Yang-Mills charge \(Q\), and the power parameter \(q\). We analyse the horizon structure and the photon region, and we compute the shadow as it appears to a remote observer for different values of these parameters. Using the published Event Horizon Telescope measurements of M87\(^*\) and Sgr A\(^*\), we constrain the Yang-Mills charge and the power parameter from the angular size and the Schwarzschild deviation \(\delta\) of the observed images. At the Maxwell point \(q = 1\) the spin marginalized likelihood combining both sources bounds the charge to \(Q \lesssim 0.26\,M\) at \(1\sigma\), while the fixed-spin band intersection at \(a = 0.7\,M\) gives the weaker \(Q \lesssim 0.52\,M\) from the M87\(^*\) angular size alone. The bound weakens as \(q \to 3/2\), where the shadow diameter becomes nearly insensitive to the charge. The shadow radius also fixes the limiting absorption cross section at high frequencies and hence the energy emission rate, which is suppressed by the charge, enhanced by the power parameter, and suppressed at near-extremal spin. We then compute the quasinormal modes of a massless scalar on the rotating background from the leading-order Wentzel-Kramers-Brillouin (WKB) conditions on the Teukolsky type radial potential, finding that the oscillation frequency rises and the damping rate falls as the charge or spin increases. The power parameter leaves an imprint on the shadow size and its charge sensitivity and in the quasinormal spectrum the shift is in principle present but lies below the resolution of current detectors.

We revisit the derivation of Morawetz--energy estimates for scalar wave equations in the domain of outer communication of a Kerr spacetime \(\KK(a,m)\). Our goal is to develop robust physical-space methods which are well suited for extension to realistic perturbations of Kerr. The proof rests on several ingredients. First, we derive conditional Morawetz estimates which extend the physical-space techniques initiated by Andersson and Blue \cite{AB}, and later adapted in \cite{GKS} to perturbations of slowly rotating Kerr, by exploiting a physical-space characterization of the full \(r\)-range of trapped null geodesics. Second, we use an idea introduced by Stogin \cite{St} in the axially symmetric case to handle the low-frequency difficulties in the Morawetz estimates. In the general case, the control of the lower-order terms also requires making full use of the principal trapping term in the Morawetz bulk norm, together with a new use of Hardy-type inequalities. A further new ingredient is the control of the boundary terms generated by the Morawetz estimates. This is based on two additional ideas: physical-space versions of Whiting's transform \cite{W}, developed in a forthcoming paper \cite{H-K2}, which yield a flux-independent energy estimate; and an adaptation of the Andersson--Blue invariant-operator method, which turns that estimate into a bound for the horizon flux. Finally, a continuity argument yields an unconditional global-in-time Morawetz estimate, while a new energy estimate is obtained from the construction of a causal vectorfield which is Killing on the trapping set. The results proved here are restricted to scalar wave equations, corresponding to spin \(0\), in the range \(|a|/m\leq 0.75\). We expect this restriction to be technical, and the methods developed in this paper to extend to the Teukolsky equation.

We investigate the repetitive Penrose process for neutral particles in a rotating four-dimensional Einstein--Gauss--Bonnet black hole obtained through the modified Newman--Janis algorithm, developing a nonlinear iterative scheme in which the mass, angular momentum, and irreducible mass are updated after each extraction event. Imposing the triple turning-point condition, we obtain a closed-form solution of the conservation equations for energy, angular momentum, and radial momentum that reduces to the Kerr result in the limit of vanishing coupling. The distinctive feature of this background is that, although the Gauss--Bonnet coupling $\alpha$ is a fixed constant of the action and is not carried by the infalling fragments, the dimensionless coupling $\hat\alpha=\alpha/M^{2}$ grows at every iteration as the mass decreases, so that the effective Gauss--Bonnet correction is self-amplified along the sequence. We find that a larger coupling lowers the extremal spin, contracts the ergosphere, and reduces the number of admissible decays, forbidding the process near the horizon at strong coupling while permitting it at larger decay radii; the termination is controlled throughout by the incident particle. The energy return on investment decreases monotonically with $\hat\alpha$ and the growth of the irreducible mass is suppressed relative to Kerr, whereas the energy utilization efficiency is non-monotonic: below a critical coupling the parameter space exhibits a four-region structure with a bounded window in which the EGB black hole is more efficient than Kerr; this four-region structure collapses into a three-region one above a critical coupling. This coupling-driven reorganization of the efficiency landscape has no analogue in the Kerr, Reissner--Nordström, Kerr--de~Sitter, accelerating Kerr, or Kerr--Newman cases.

We present a concise and explicit analysis of logarithmically corrected black-hole thermodynamics and scalar scattering on the Schwarzschild branch of symmetric teleparallel gravity. Treating the metric and the flat, torsion-free affine connection as independent variables, we formulate the relevant nonmetricity geometry and field equations and show that the linear branch is dynamically equivalent to general relativity up to a boundary term. The vacuum solution is therefore the Schwarzschild spacetime. The leading entropy is derived from both the Noether-charge method and the classical first law, after which a logarithmic correction is introduced. When the geometry and ADM mass are kept fixed, the geometric Hawking temperature remains unchanged, whereas the temperature defined through the corrected first law is modified. The apparent divergence of the heat capacity occurs outside the regime in which the logarithmic expansion is reliable and therefore cannot be interpreted as a physical phase transition. We also derive the scalar radial equation, effective potential, conserved Wronskian, and reflection-transmission relation. For a neutral scalar field on a static neutral background, no superradiant amplification occurs, and the entropy correction produces no first-order change in the scattering amplitudes unless a genuine semiclassical backreaction or an explicit rotating or charged black-hole solution is provided.

Recently, we demonstrated that while an interstellar mission to the nearest black hole remains highly speculative and extraordinarily challenging, it is not entirely implausible within the coming decades. Given that such a mission would likely take about a hundred years and require substantial financial and human investment, it is essential to assess whether it could investigate black holes and test General Relativity to a degree that cannot be achieved by Solar System observatories for the foreseeable future. In Paper I, we assumed the capability to decelerate the spacecraft and presented a preliminary study of how orbiting probes could test the nature of the compact object. In this second paper, we study how the black hole can be tested without decelerating the spacecraft, using flyby probes.

It has been argued that degenerate higher-order scalar-tensor theories and the effective field theory (EFT) of dark energy are endowed with the Vainshtein mechanism, resulting in a screened fifth force in the exterior of a gravitational source. However, spherical symmetry has been assumed in most of the discussions so far. In this paper, we study whether the Vainshtein mechanism operates in the EFT of dark energy beyond spherical symmetry, focusing in particular on the role of the ``beyond Horndeski'' EFT parameters. Assuming that deviations from spherical symmetry are small, we compute multipole moments of the gravitational potential for a given nonspherical source. For a generic choice of the ``beyond Horndeski'' EFT parameters, it is shown that the multipole moments of the fifth force are not screened in the region where the monopole component is screened. Rather, the gravitational potential shows a characteristic oscillatory behavior in its multipole components. In the special case where the EFT parameters are tuned so that graviton decay into dark energy is practically absent, the behavior of the multipole moments is qualitatively different from that in the generic case. However, also in this case, the Vainshtein mechanism is not efficient enough to screen the fifth force around the source.

Non-Gaussian noise transients ("glitches") in gravitational-wave observatories degrade our ability to accurately perform astrophysical inference. We present the analysis pipeline bilby_glitch, which allows for simultaneous Bayesian inference of gravitational-wave signals and glitches. Our framework is modular and built on top of the popular bilby framework, facilitating future extensions with additional glitch and signal models. We integrate transdimensional bilby into our framework and discuss three glitch models: a physically-motivated slow scattering model, and flexible sine-Gaussian and chirplet models. Using a combination of simulated and real data, we demonstrate that bilby_glitch produces reliable results. We then reanalyse two gravitational-wave events - GW191109 and GW200129 - which show signs of interesting black-hole spins, but which may also be affected by data-quality issues. Our results for GW191109 are consistent with previous analysis. For GW200129, we recover results consistent with Payne et al., where the evidence of spin-precession is much weaker when using the waveform approximant NRSur7dq4 in combination with wavelet-based glitch modeling. Furthermore, we show the astrophysical conclusion of this event is dependent on the interplay between the waveform approximant and glitch model, since in contrast to NRSur7dq4 we find that inference with the waveform approximant IMRPhenomXPHM shows strong evidence of spin-precession when used in combination with wavelet-based glitch modeling.

We investigate the influence of medium effects on strange quark matter and their consequences for the structural properties of compact stars. In this study, the bag constant, in the MIT bag model equation of state, is reformulated as a function of the chemical potential of quark. Imposing the Bodmer-Witten stability criterion, the parameter space is constrained by evaluating the energy per baryon. The Tolman-Oppenheimer-Volkoff equations are then solved to obtain the maximum mass-radius configurations. Our analysis shows that an increase in chemical potential leads to a reduction in the effective value of bag constant, resulting in a stiffer equation of state and correspondingly higher value of maximum stellar mass. Furthermore, we examine the chemical potential dependence of the tidal Love number and tidal deformability. The results demonstrate that, for the chosen set of parameters, the constraint from the GW170817 event, namely $\Lambda < 800$, is consistently satisfied. In this paper, we have tried to establish how chemical potential $(\mu)$ affects the maximum mass and tidal deformability of strange stars.

The James Webb Space Telescope (JWST) has revealed compact, red, overmassive accreting black holes - the so-called ``Little Red Dots'' (LRDs) - in chemically near-pristine hosts at $z\simeq5 - 9$, straining standard heavy-seed models. We show that a population of strongly clustered primordial black holes (PBH) with a broad mass function predicted by a QCD-epoch thermal history naturally realizes the configuration that assembles LRD-scale seeds: an intermediate-mass PBH \emph{nucleus} $M_{\rm BH}\sim10^3$-$10^5\,M_\odot$ surrounded, within a few parsecs, by a swarm of light ($m\sim30\,M_\odot$) PBHs embedded in dense baryonic gas. Gas dynamical friction keeps the loss cone full and lets the core contract, so the swarm sinks and is swallowed on $t_{\rm seed}\sim10$-50 Myr, well inside the cosmic time at $z\sim10$-$15$. Because a heavy nucleus is present \emph{ab initio}, the captures occur at extreme mass ratio $q\sim10^{-4}$-$10^{-2}$: the remnant is retained against gravitational recoil, and each capture reaches the innermost stable orbit under gravitational-wave (GW) emission, radiating $\simeq0.06\,m c^2$ so that the assembly efficiency is $\zeta\simeq0.06$ independent of $M_{\rm BH}$. The superposed swarm inspirals form a stochastic background $\Omega_{\rm GW} h^2\sim10^{-13}$-$10^{-11}$ with a $\Omega_{\rm GW}\propto f^{2/3}$ shape truncated below the gas-decoupling frequency and topped by a ringdown ``comb'' at $f_{\rm ring}(M_{\rm BH})\simeq13$ mHz for $10^5\,M_\odot$ and $\simeq1.3$ Hz for $10^3\,M_\odot$ nuclei at $z_f\simeq12$. The few comparable-mass nucleus-nucleus coalescences are instead individually resolvable LISA/deci-Hz sources. Detection, and discrimination of these signatures from a directly formed PBH seed of the same mass, would identify the LRDs as PBH-nucleus seeded black holes.

Extreme mass-ratio inspirals (EMRIs) are sensitive probes of weak environmental effects around massive black holes, since such effects can accumulate into observable gravitational-wave phase shifts. In this work, we study the phase degeneracy between dark matter halos and accretion disks in eccentric EMRI waveforms. We model the dark matter (DM) environment with NFW and Beta halo profiles, and describe the disk using a thin $\alpha$-disk model. Their distinguishability is quantified through eccentricity-dependent phase diagnostics and residual signal-to-noise ratios in the LISA band. Our results show that DM-induced dephasing depends only weakly on the initial eccentricity $e_0$, whereas disk-induced dephasing is strongly suppressed as $e_0$ increases. The distinguishability time is longest for circular orbits and decreases rapidly for slightly eccentric orbits. For the benchmark systems considered here, the DM--disk waveform difference can be detectable by LISA, and $e_0$ can serve as an auxiliary diagnostic in addition to the observation duration.

We present the first self-force-based beyond-GR waveform model incorporating post-adiabatic orbital evolution for intermediate- and extreme-mass-ratio inspirals in theories of gravity with additional scalar fields. Focusing on quasi-circular inspirals into a non-spinning primary, we combine a first post-adiabatic (1PA) gravitational sector with leading-order scalar field effects and use Bayesian injection-recovery studies to assess the impact of waveform systematics on the inference of scalar charges with LISA. We find that neglecting 1PA effects in the gravitational sector can bias the inference of intrinsic binary parameters, while scalar-charge measurements remain robust across a wide range of mass ratios. In contrast, analysing signals from binaries in which the secondary carries a scalar charge using pure-GR templates leads to significant biases and underestimated uncertainties due to unmodelled correlations between the scalar charge and the binary parameters. We also investigate the role of secondary spin and find no significant correlation between the secondary spin and the scalar charge. Notably, up to a mass ratio of $10^{-4}$, the secondary spin itself remains unconstrained even in the pure-GR case, in contrast with previous claims in the literature. Finally, we show that modelling scalar emission with a leading-order dipolar post-Newtonian approximation -- for quasi-circular inspirals into a non-spinning primary -- introduces negligible systematic errors relative to fully relativistic scalar fluxes.

The Einstein-de Sitter universe is the prevailing model used in cosmology to describe the cold dark matter-dominated epoch of the universe. This model is a spatially homogeneous and isotropic spacetime undergoing decelerated expansion, and is linearly unstable under the Einstein-Euler equations with a pressureless fluid equation of state. We show that every initial data set for the Einstein-Euler equations on $\mathbb{T}^3$ with a near-flat metric and positive fluid energy density converges to a flat metric under the Einstein-Euler flow with a polytropic equation of state. This means the metric asymptotes to an Einstein-de Sitter spacetime. In particular, this settles the question of whether the Einstein-de Sitter model can be nonlinearly stable for an appropriate matter model.

Millihertz gravitational-wave observations with space-based interferometers require time-delay interferometry (TDI) observables whose residual instrumental noise is sufficiently controlled for both detection and parameter inference. Although TDI suppresses laser phase noise in unequal and time-dependent arms, clock jitter from onboard ultra-stable oscillators can remain above the secondary-noise floor and bias the effective noise weighting used in data analysis. We formulate a clock-noise subtraction scheme directly in the geometric-TDI framework. The construction introduces generalized clock-noise observables for the four space-time link structures that arise when both delay and time-advance operators are allowed. This makes the clock-noise residual algebraically parallel to the laser-noise residual and yields explicit subtraction terms for arbitrary two-path geometric TDI observables. We illustrate the method with representative first- and second-generation geometric TDI combinations, and test it with time-domain simulations using LISA-like orbits and noise levels. For a modified second-generation U-type observable, the subtraction suppresses the clock-noise residual below the signal region, restores the expected sensitivity to a monochromatic source, and improves the Fisher and Markov-chain Monte Carlo parameter constraints on the source amplitude, frequency and phase. These results show that clock-noise calibration is a necessary component of precision data analysis for future space-based gravitational-wave detectors.

We formulate a generally covariant six-field Rational Extended Thermodynamics model (RET$_6$) for relativistic polyatomic gases, with the dynamical pressure as the only non-equilibrium variable. The model is based on a polyatomic extension of the Boltzmann-Chernikov kinetic equation, where the one-particle distribution depends also on an internal-energy variable, and on the Maximum Entropy closure of the associated relativistic moment hierarchy. The resulting field equations, closure relations, and production term are therefore fixed by the underlying kinetic structure rather than postulated phenomenologically. We extend the RET$_6$ model from Minkowski spacetime to a general curved spacetime by the minimal coupling prescription and couple it to the Einstein equations. As a first structural result, we prove a kinetic-theory no-go theorem in this polyatomic RET setting stating that any stress-energy tensor induced by a non-negative relativistic one-particle distribution function satisfies the strong energy condition. We then specialize the theory to a homogeneous and isotropic Friedmann-Lemaître-Robertson-Walker (FLRW) spacetime. In this setting the dynamical pressure modifies the expansion dynamics with respect to the perfect-fluid Euler case, but the no-go theorem excludes acceleration driven by the RET$_6$ gas alone. Finally, we reintroduce a cosmological constant and study the combined $\Lambda$RET$_6$ model, proving the existence and local stability of a de Sitter attractor at late times. Numerical integrations show that, for physically motivated post-recombination initial data and relaxation times, the expansion history rapidly approaches that of $\Lambda$CDM, with small non-equilibrium corrections controlled by the relaxation time and by the initial value of the dynamical pressure.

We present a numerical relativity study of head-on collisions involving boson stars using initial data inspired by the Bowen-York initial data used to model black hole binaries with punctures. The initial data method preserves the simplicity of the Bowen-York approach, thus allowing incorporating information from the early, post-Newtonian inspiral phase in binary coalescences. We test the method on a single boson star with linear momentum. We present results from head-on collisions of boson stars as well as encounters of boson stars with black holes. In general, the results are consistent with previous studies, demonstrating the effectiveness of the initial data method. In particular, we show that boson star head-on collisions emit more energy in gravitational waves than the equivalent black hole binaries. On the other hand, head-on collisions of a boson star with a black hole radiate less than their black hole binary counterparts.

Cones of future and past are rigorously constructed under the horizon of black hole by completions of geodesics continued from causally connected space-time regions outside the black hole interior. Treating the Schwarzschild black hole as a zero charge limit of Reissner--Nordsrøm black hole reforms the Penrose--Carter diagram into the infinite band that excludes the closed proper-time cycles under the geodesic motion. The marginal trajectories between the cones of future and past compose paths common with a compact non-Hausdorff spherical extension of black hole interior forming the thermal bath for particles fallen to the black hole.

The centre of mass (CoM) of compact binary coalescences (CBCs) occurring in the vicinity of a supermassive black hole, through interaction with an arbitrary third body (e.g., of stellar mass), or in a dense stellar environment, will undergo a time-varying line-of-sight (LOS) velocity. This in turn leads to a time-varying Doppler shift and corresponding modulations in the shape of the gravitational waves (GWs). The phase and amplitude corrections arising from constant LOS acceleration and its higher-order time derivatives are already known. Specifically, these effects lead to corrections to the GW waveform at $-4n$ post-Newtonian (PN) order, where $n$ is the $n^{th}$ time derivative of the LOS velocity. In the context of a circular or eccentric outer orbit of the CoM of the CBC, these effects can be thought of as approximations to the LOS velocity in the limit: observation duration $\ll$ period of the outer orbit. However, this condition is not necessarily always satisfied. In this {\it paper}, we present phase and amplitude corrections to the GW waveforms arising from a periodic non-relativistic LOS velocity for circular and eccentric outer orbits of the CBC's CoM. Specifically, these lead to phase and amplitude modulations at 4 PN order, and reduce to the known corrections for constant kinematic parameters under appropriate limits mentioned above. We also perform a Fisher matrix analysis to forecast constraints on the environment that is sourcing the time-varying LOS velocity, for various future ground and space-based detectors. We further show that constraints acquired using GW waveforms derived in this work improve significantly in comparison to those acquired from approximate methods valid for constant kinematic parameters.

Preparing massive particles in coherent spatial superpositions is a central objective of modern quantum science, motivated by applications ranging from fundamental tests of quantum mechanics and gravity to quantum-enhanced sensing. The experimental difficulty of realizing such superpositions is usually attributed to environmental decoherence mechanisms whose impact depends on the details of the experimental implementation. Here we identify a universal constraint arising from momentum conservation and the quantum nature of the preparation apparatus. Any protocol that places a particle of mass $m$ in a spatial superposition with separation $d$ necessarily entangles the particle with the center-of-mass degree of freedom of the apparatus responsible for the splitting. The resulting recoil displacement, fixed by conservation of the mass dipole moment, reduces the coherence of the particle when the apparatus is not included as part of the quantum system. For an apparatus of mass $M$, preserving coherence requires the recoil displacement to remain smaller than the coherence length of the apparatus center-of-mass state, leading to a quantitative bound expressible as a constraint on its temperature and on how rigidly the apparatus is anchored to the laboratory frame. We analyze the implications of this bound for current matter-wave interferometry experiments, proposals for gravitationally mediated entanglement, and tests of quantum mechanics near the Planck scale. Our main result, which may seem counterintuitive, is that the recoil of even heavy macroscopic apparatuses can pose a surprisingly strong constraint on the coherence of spatial superpositions of particles with masses well below the Planck mass. Finally, we discuss why the resulting limitation should be regarded as a conservative estimate and under which conditions it can be interpreted as an instance of false decoherence.

Heliospheric density variations impart delays on pulse times of arrivals from millisecond pulsars. Improper modelling of these variations may affect gravitational wave detection and characterisation by pulsar timing arrays (PTAs). Currently, PTAs typically employ a time-varying, spherically symmetric heliosphere model, which does not capture the full spatial and temporal complexity of the heliosphere. Instead, we investigate whether a three-dimensional, time-dependent model of the inner heliosphere from interplanetary scintillation (IPS) measurements - the IPS-UCSD model - can be employed to mitigate the solar wind in PTA analyses. We applied the IPS-UCSD model to the MeerKAT PTA 4.5-year dataset to assess whether it could correct for heliospheric density variations, and the impact on GW sensitivity compared to a spherically-symmetric model. We find that the model does not accurately correct for heliosphere-induced timing distortions, leading to bias in recovered GW parameters. Using simulations, we show that the spherically symmetric heliosphere model also fails to fully capture heliospheric density variations like those in the IPS-UCSD model. However, if interstellar dispersion measure (DM) variations are also modelled, then the heliospheric model errors are partially absorbed by DM variations, reducing contamination of the GW signal. Therefore we find that a time-varying spherically symmetric model is sufficient to mitigate the effect of heliospheric time delays on recovered GW results at typical PTA radio frequencies, provided other signal components are also modelled. We propose that the most precisely timed pulsars may be used to improve data-driven heliospheric density models in the future.

The maximum mass of neutron stars provides a key constraint on the equation of state (EoS) of dense matter. Recent observations, including the ${\approx}2 M_{\odot}$ pulsar PSR~J0740+6620, have placed strong constraints on a large class of soft EoSs, while the possible existence of a compact object with a mass of $2.50$ - $2.67$ $M_{\odot}$ in GW 190814 further challenges our understanding of dense matter. Moreover, the inclusion of hyperonic degrees of freedom generally softens the EoS, making it difficult to support massive neutron stars even when the $2$ $M_{\odot}$ constraint is satisfied (a problem known as the hyperon puzzle). In this work, we investigate whether differential rotation can enhance the maximum mass of neutron stars constructed with an EoS including hyperons, thereby addressing the maximum-mass constraints imposed by current observations. We employ the Cook-Shapiro-Teukolsky (CST) approach, a numerically improved reformulation of the Komatsu-Eriguchi-Hachisu (KEH) scheme, to construct equilibrium configurations of differentially rotating neutron stars. For the nuclear matter EoS, we adopt a relativistic mean-field (RMF) model incorporating hyperonic degrees of freedom through an SU(6) symmetric coupling scheme. We find that differential rotation can substantially increase the maximum mass, yielding configurations consistent with the mass range inferred from GW 190814. However, a sufficiently soft EoS fails to satisfy the constraint from PSR~J0740+6620 (346 Hz) even with differential rotation applied. We also present a systematic analysis of the internal structure of the resulting equilibrium configurations. Furthermore, we demonstrate the existence of quasi-toroidal configurations and present equilibrium sequences incorporating the full baryon octet under extreme differential rotation.

The enhanced X-ray Timing and Polarimetry (eXTP) mission will combine spectral, timing, and polarimetric techniques to study accreting black holes, measure their masses and spins, and test Einstein's theory of General Relativity in the strong-field regime. In this contribution, I review the capabilities of eXTP to advance our current understanding of black hole physics and astrophysics.

Neutron stars, due to their extremely high matter density and strong magnetic field, provide the best environment for exploring new physics beyond the Standard Model of particle physics. In this work, we study the effect of pre-existing dark matter component and an internal magnetic field on the structural properties of neutron stars. We employed relativistic mean field theory based equations of state and used a single fluid approach for solving the Tolman-Oppenheimer-Volkoff (TOV) equation to compute properties like mass-radius, tidal deformability, compactness, and non-radial oscillation frequencies. We consider the following two scenarios for equation of state (EoS): (1) density-independent couplings along with non-linear interactions of mesons, and (2) density-dependent couplings, with only considering linear interactions for mesons. These mesons mediate the interactions between nucleonic constituents of a neutron star. In the dark matter sector we consider a massive fermionic dark matter which interacts with the nucleons through a Higgs portal interaction. We explore parameter regions for Fermi momentum of dark matter in the range $k_F = 0.01$ GeV - $0.06$ GeV, and two different values of the mass of fermionic dark matter, $M_\chi = 200$ GeV and $300$ GeV. We consider two values of the central magnetic field, $B_c = 7\times10^{17}$ Gauss, $9 \times 10^{17}$ Gauss, for a magnetized neutron star. Finally, we compare the theoretical predictions with the observed mass-radius and tidal deformability data of pulsars obtained from gravitational wave observations.

We present updated constraints on both flat and non-flat Dvali-Gabadadze-Porrati (DGP) cosmological models using the latest baryon acoustic oscillation (BAO) measurements from the Dark Energy Spectroscopic Instrument Data Release 2 (DESI DR2), in combination with cosmic chronometer (CC), Type Ia supernova (SNIa), and cosmic microwave background (CMB) distance priors. For the non-flat DGP model, we obtain $H_0 = 64.05 \pm 0.27\, \rm{kms^{-1}Mpc^{-1}}$, $\Omega_m = 0.3264 \pm 0.0043$, and $\Omega_k = 0.0088 \pm 0.0016$, corresponding to a transition redshift $z_t \sim 0.41$. For the flat case, the constraints are $H_0 = 63.28 \pm 0.25\, \rm{kms^{-1}Mpc^{-1}}$ and $\Omega_m = 0.3303 \pm 0.0036$. In both scenarios, the inferred Hubble constant is significantly lower than the Planck $\mathrm{\Lambda}$CDM value, indicating that the DGP framework does not alleviate the Hubble tension. Current observations strongly disfavor the DGP framework, primarily due to its inability to simultaneously accommodate DESI BAO and CMB this http URL incorporating the latest high-precision DESI observations within a unified analysis framework, this work provides updated and more stringent limits on the DGP scenario, offering a consolidated assessment of its viability in the context of current cosmological data.

In this note we investigate a notion of stability for spacelike cross sections of a null cone under area preserving variations that has been introduced in previous work by Kröncke and the author. Here, we consider null cones with spherical cross sections in a $4$-dimensional spacetime and show that the Hawking energy of a stable cross section admits a non-negative lower bound provided the dominant energy condition holds. Similar to a recent work by Peñuela Diaz, we show that under an additional assumption the Hakwing energy is zero if and only if the stable cross section embeds isometrically into the Minkowski lightcone. As a main result, we show that the only stable cross sections of the standard Minkowski lightcone are round spheres.

In this work, we investigate quantum complexity diagnostics of primordial curvature perturbations within the inflationary paradigm. We compare canonical scalar-field inflation with the modified gravity model $f(\phi,R)$, focusing on the evolution of the two-mode squeezed state generated by the coupling between the $\vec{k}$ and $-\vec{k}$ momentum sectors. Starting from the quadratic action for curvature perturbations, we derive the evolution equations for the squeezed strength $r_k$ and squeezed angle $\phi_k$, utilizing them to evaluate both circuit complexity and Krylov-space diagnostics. Specifically, we compute the Krylov complexity, Krylov entropy, Lanczos coefficients $b_n$, and an effective dissipative contribution $c_n$ within an open-system extension. Our numerical results demonstrate that the $f(\phi,R)$ coupling enhances the squeezed strength relative to the canonical scalar field inflation. Since the Krylov complexity of the two-mode squeezed state is directly controlled by the mean pair number ($K=\sinh^2 r_k$), this enhancement leads to a smaller growth in Krylov complexity and related Krylov-space quantities. Furthermore, circuit complexity displays a more pronounced evolution in the $f(\phi,R)$ framework, particularly after the horizon exit regime. Ultimately, our work sheds new light on the quantum complexity of modified gravity $f(\phi,R)$.

We investigate the dynamics of domain walls in scalar field theories with degenerate vacua (i.e., vacua of equal energy density) in which the scalar field mass depends on the vacuum state. Using analytical arguments and numerical simulations, we show that this vacuum dependence of the scalar field mass renders the emission of scalar radiation from domain walls anisotropic, preferentially toward regions with smaller scalar field mass. We further show that the resulting recoil (rocket) effect biases the evolution of cosmological domain wall networks in favor of the lower-mass vacuum, thereby promoting network decay. We also demonstrate that the biased evolution of domain walls in theories with degenerate vacua, previously attributed to asymmetries of the potential barrier near the local maximum, is instead primarily controlled by the vacuum dependence of the scalar field mass. More generally, in theories with non-degenerate vacua, this recoil mechanism constitutes an additional source of dynamical bias that can either hasten or delay network decay relative to the standard expectation based solely on differences in vacuum energy density.

Exoplanets are high-value targets for a variety of ground and space-based telescopes. All known exoplanets are Galactic, and a fraction of them orbit compact objects. In this work, we investigate the possibility of detecting extragalactic exoplanets orbiting stellar-mass compact binary coalescences (CBCs), such as binary neutron stars, neutron star-black holes, and binary black holes, using future gravitational wave (GW) detectors, including A+ (LIGO in O5), Einstein Telescope, and DECIGO. We use the technique of reconstructing an external potential's profile by extracting information about the centre-of-mass (CoM) kinematics of a CBC encoded in the GWs it emits. In this work, the external potential is provided by the circum-CBC exoplanet, and the resulting signature on the GW waveform comes from the ``wobble'' of the CBC's CoM around the CBC-exoplanet barycentre. As a proof of principle, we consider a few example CBCs detectable with future detectors and a range of circum-CBC exoplanet parameters in circular and eccentric orbits. We find that for a significant fraction of the range of parameters considered, we can identify the presence of a circum-CBC exoplanet by extracting its mass (up to an unknown orbital inclination angle) within a factor $\mathcal{O}(1)$ of its true value, at $68\%$ confidence.

We investigate Unruh-DeWitt detectors coupled to composite observables of a quantum scalar field, including quadratic coupling to the field momentum and coupling to the local energy density. We develop a distributional framework for evaluating the corresponding detector response functions and apply it to detectors crossing the Rindler firewall. While we recover the finite response of the derivative-coupling model, we show that quadratic momentum coupling leads to ill-defined products of distributions and unavoidable formal $\delta(0)$-type divergences. Since the local energy-density response is closely tied to the quadratic momentum response, our results provide strong evidence that the standard sharp firewall model is incompatible with nonlinear detector couplings to local observables. Our analysis further suggests that these pathologies originate from the discontinuous severing of correlations across the Rindler horizon, rather than from the detector model itself.

The endpoint of black hole evaporation remains uncertain once the semiclassical description approaches the Planck scale. In this work we study late-stage evaporation within four-dimensional gravitational effective field theory. We consider the leading local correction to the Schwarzschild solution arising from a cubic curvature operator, and use the corrected geometry to analyze the resulting evaporation dynamics and associated thermodynamic properties. We show that the cubic correction induces a parametric slow-down of the evaporation rate at small masses, which within the truncated theory can appear as a freeze-out at a finite mass scale. We demonstrate that this behavior is not an independent physical prediction, but instead occurs precisely when the dimensionless expansion parameter of the effective theory becomes of order unity. The corresponding mass scale coincides parametrically with the onset of Planckian curvature at the horizon, establishing that the evaporation dynamics provide a direct diagnostic of the breakdown of the effective field theory. A scaling analysis of higher-order curvature operators shows that once the cubic term becomes comparable to the Einstein-Hilbert contribution, generic higher-order terms are no longer parametrically suppressed. The apparent remnant-like behavior therefore arises at the boundary of validity of the effective description rather than within a controlled perturbative regime. These results demonstrate that late-stage evaporation encodes the limits of gravitational effective field theory, providing a dynamical criterion for its breakdown.

We study the evolution of cosmological density perturbations in massive conformal gravity (MCG). We show that conformal fermionic matter alone does not generate growing density perturbations in the subhorizon regime. By introducing a conformally coupled scalar field, however, an effective cold dark matter component emerges at the effective level. The resulting coupled perturbation equations admit growing solutions with a stronger effective gravitational interaction, allowing cosmic structure formation in MCG and potentially favoring earlier structure formation at high redshifts.

Smooth window functions are often applied to strain data when inferring the parameters describing the astrophysical sources of gravitational-wave transients. Within the LIGO-Virgo-KAGRA collaboration, it is conventional to include a term to account for power loss due to this window in the likelihood function. We show that the inclusion of this factor leads to biased inference. The simplest solution to this, omitting the factor, leads to unbiased posteriors and Bayes factor estimates provided the window does not suppress the signal for signal-to-noise ratios $\lesssim O(100)$, but unreliable estimates of the absolute likelihood. Instead, we propose a multi-stage method that yields consistent estimates for the absolute likelihood in addition to unbiased posterior distributions and Bayes factors for signal-to-noise ratios $\lesssim O(1000)$. Additionally, we demonstrate that the commonly held wisdom that using rectangular windows necessarily leads to biased inference is incorrect.

Modified dispersion relations (MDRs) arise in many quantum-gravity approaches, often in non-polynomial or non-analytic form beyond the reach of effective field theory (EFT). Logarithmic, exponential and trigonometric MDRs appear in causal set theory, nonlocal gravity and $\kappa$-Poincaré models, while Loop Quantum Gravity (LQG) yields polymeric (sine), holonomy, inverse-triad and semiclassical corrections. Using the geometric framework of Ref.~\cite{GRP}, we analyse the intrinsic curvature of the associated energy--momentum surfaces, where negative curvature ensures hyperbolic and stable propagation, and curvature sign changes or critical points indicate kinematical instabilities or new invariant scales. We apply this method exhaustively to all major MDRs derived in LQG and find that they remain strictly hyperbolic in the entire phenomenologically relevant regime, with no elliptic patches or critical branching. The same framework provides universal constraints on representative logarithmic, exponential and trigonometric MDRs beyond EFT. Thus, geometric criteria yield a unified and coordinate-independent assessment of stability, thresholds and invariant scales, and demonstrate the robustness of MDRs emerging from LQG.

An extremal Reissner-Nordström black hole can form in finite time in the gravitational collapse of a massless charged scalar field. The proof of this is based on the method of characteristic gluing, which involves making an Ansatz for the scalar field at the horizon. We perform a numerical investigation of the characteristic gluing procedure for several different Ansätze. In each case, gluing is possible only if the final black hole mass is large enough. We find that the minimum required mass varies significantly for different Ansätze. We also consider the effect of including a mass term for the scalar field. In this case, for each Ansatz we determine the maximum mass-to-charge ratio for the scalar field such that gluing is possible. Analogous results are obtained for a non-zero cosmological constant.

Previous studies suggested that the particle circular orbit can serve as a probe of black hole phase transitions. However, these studies only identified this phenomenon by substituting the horizon radius $r_h$ with the circular orbit radius $r_c$ in thermodynamic state relations. Such simplistic substitution fails to uncover the underlying connection between black hole phase transitions and particle circular orbits. In this work, we successfully establish this profound intrinsic link by deriving a differential relation for $r_c$ that relates to thermodynamic parameters and the first law of black hole thermodynamics. Using this relation, we demonstrate that during a first-order phase transition, if $r_h$ experiences a discontinuous jump (such as in the small/large black hole phase transition), then $r_c$ must simultaneously undergo a discontinuous jump. This finding confirms that particle circular orbits can indeed serve as probes of first-order phase transitions. More importantly, we show that this phenomenon is a direct consequence of the nonzero latent heat inherent to first-order phase transitions. Finally, we demonstrate that the jump sizes $\Delta r_c$ and $\Delta r_h$ across the phase transition share the same critical exponent at the thermodynamic critical point, indicating that $\Delta r_c$ can serve as an order parameter for black hole phase transitions. Notably, this conclusion follows directly from the first law.

Rotating traversable wormholes provide a horizonless setting in which to investigate wave dynamics beyond the separable structures familiar from black-hole perturbation theory. We study scalar perturbations in the rotating AdS-Teo wormhole and show that the absence of separability naturally leads to a coupled-channel formulation in which the angular harmonic modes interact through a matrix-valued Sturm-Liouville operator. Imposing regularity at the wormhole throat together with asymptotically anti-de Sitter boundary conditions yields a determinant quantization condition that determines a discrete normal-mode spectrum. A controlled two-channel truncation illustrates how angular-channel mixing produces frequency shifts, spectral repulsion, and collective mode reorganization. From the asymptotic solutions, we construct a matrix-valued boundary response function whose poles coincide with the bulk normal-mode frequencies, while its off-diagonal components provide a direct signature of rotation-induced channel mixing. We further investigate the renormalized vacuum polarization, whose interference terms reveal local quantum signatures of non-separability, and examine semiclassical geodesic correlators as complementary probes of two-boundary connectivity. These results suggest that coupled-channel spectral theory provides a natural organizing principle for rotating, non-separable geometries, replacing conventional mode separability with a framework based on collective normal modes, matrix-valued response functions, and coupled quantum observables.

In this study, we examine the role of a scalar field in the evolution of the Universe within the framework of a Bianchi type-I cosmological model with Lyra's geometry. Previous research has explored the nonlinear spinor field in various anisotropic and isotropic cosmological models. In our current study, we and dynamical restrictions for Lyra parameters and violation of stress-energy tensor conservation within Lyra geometry. We shown that in considering cases behavior of Lyra's parameter corresponds to relative influence in early universe and absence of Lyra geometry in present universe.

Fast and reliable inference of gravitational-wave source parameters is crucial for analyzing large catalogs that are reaching the size of hundreds of detections, and for identifying short-lived electromagnetic counterparts. Neural posterior estimation has emerged as a powerful inference method, where the model is trained on simulated gravitational-wave data at considerable computational cost, but thereafter enables extremely fast and inexpensive inference at test time. Here, we extend this approach by incorporating domain-specific physical insights and methods in the model architecture. These include compressing the data by heterodyning against a reference waveform chosen via approximate likelihood maximization, removing parameter degeneracies through tailored coordinate systems, and eliminating known multimodalities by folding the parameter space. As a result, the network is approximately equivariant to changes in the source parameters, and achieves a reduced training cost and improved model interpretability. Our implementation, called labrador, can be trained end-to-end on a 1-day timescale on $\sim 10^2$ CPU cores and a V100 GPU, achieving a median importance-sampling efficiency of 1% on quadrupolar, aligned-spin signals in a broad mass range (chirp mass $\mathcal{M} \in 1\text{-}50\,\mathrm{M}_\odot$, mass ratio $q > 0.1$). labrador is the first neural inference code to achieve extensive coverage of long-duration signals with secondary masses $m_2 < 10\,\mathrm{M}_\odot$, rendered possible by its equivariance property. Among our novel contributions is a numerically stable procedure that enables neural posterior estimation when the simulation and inference priors differ.

We show that cosmological models with a semi-infinite phase of slow contraction (ekpyrosis) possess a combination of properties that can address several fundamental problems in cosmology, otherwise faced in contracting de Sitter phases or standard big bang expansion. In particular, slow contraction admits a stable past attractor asymptoting to Minkowski space, as well as a stable, flat, homogeneous, and isotropic future attractor with negligible Weyl curvature (and, therefore, negligible gravitational entropy). In bouncing cosmologies, this contracting attractor is terminated by a smooth, non-singular bounce that transforms the attractor properties at the end of contraction into the initial conditions for the subsequent expanding phase. Cosmologies incorporating a slow contraction phase have no particle horizon and therefore avoid the causal horizon problem. The past Minkowski attractor also generates an initial spectrum of vacuum-like quantum fluctuations on all wavelengths. Moreover, because the averaged expansion rate along past-directed geodesics is non-positive, models incorporating a semi-infinite phase of slow contraction also evade the Borde,Guth and Vilenkin theorem and are past geodesically complete. By contrast, contracting de Sitter space possesses a finite particle horizon and becomes unstable in the presence of scalar fields, matter, or radiation.

The LIGO-Virgo-KAGRA consortium has sporadically detected inspiral-dominated gravitational-wave events such as GW170817 and GW190425. These events offer an opportunity to constrain possible initial (residual) orbital eccentricities using purely inspiral template families. We detail the implementation of an LALSuite approximant, TaylorF2Ecck, which analytically models inspiral gravitational waves from non-spinning compact binaries in Post-Newtonian-accurate eccentric orbits and restricts the initial-eccentricity contributions to leading order. Specifically, our frequency-domain approximant consistently incorporates orbital, advance of periastron, and gravitational-wave emission effects fully up to 3PN order. We conduct detailed parameter-estimation studies of GW170817 and GW190425 using TaylorF2Ecck, following comprehensive sanity checks to validate model performance and investigate the influence of eccentricity and periastron advance in the relevant parameter space. The results indicate that the initial eccentricity at 20 Hz is negligible within the 90 percent credible intervals, and Bayes factors show no strong evidence favoring the eccentric waveform over the quasi-circular waveform. At such negligible initial eccentricities, comparisons between eccentric models with and without periastron advance show no clear signature of this effect, with no significant model-dependent shifts in the posterior distributions and no strong Bayes-factor evidence favoring one model over the other. Additionally, these detailed studies reveal the importance of incorporating initial-eccentricity contributions at least up to 3.5PN order and discuss its implications. We substantiate this inference by employing versions of the quasi-circular TaylorF2 approximant that incorporate Fourier phase contributions beyond the conventional 3.5PN order.

Supertranslations are usually defined as asymptotic symmetries associated with spacetime boundaries, such as null infinity and black hole horizons. In this Letter, we show that supertranslations admit a natural, coordinate-independent extension into the bulk of spacetime, realized as transitions between families of null hypersurfaces. This construction applies to generic spacetimes admitting null boundaries with residual symmetries and unifies the realizations of supertranslations at null infinity and finite-distance null hypersurfaces such as black hole horizons. The bulk supertranslation is connected to boundary supertranslation by characteristic flows. The associated symmetry algebra at the linearized level can be realized by light-ray operators defined on the null hypersurface and the bulk supertranslation acts as a zero-mode operator in the context of light-cone quantization. Within this framework, the gravitational wave memory effect corresponds to a shift of null hypersurfaces in the bulk. As explicit examples, we compute bulk supertranslations in Minkowski spacetime and four-dimensional Schwarzschild spacetime, where we uncover a novel curvature-dependent memory effect with observable consequences for light propagation.

Gravitational wave (GW) spectral sirens offer a promising method for measuring cosmological parameters using GW data only - without relying on external redshift information such as electromagnetic counterparts or galaxy catalogs - by exploiting distributional features in the population of GW sources. The advent of third-generation detectors like the Einstein Telescope (ET) will provide catalogs three orders of magnitudes larger than current ones, raising questions about the scalability and robustness of existing inference pipelines. We present a blinded mock data challenge that tests three public pipelines with distinct numerical implementations, namely, $\texttt{ICAROGW}$, $\texttt{CHIMERA}$, and $\texttt{pymcpop-gw}$, on simulated ET observations containing the best $\mathcal{O}(10^4)$ binary black hole mergers that can be observed in 1 year. We assess their computational performance, validate their agreement in a blinded setting, and forecast cosmological constraints. We find that, thanks to GPU acceleration, these pipelines can process the events expected from ET within a manageable timeframe. All pipelines recover consistent cosmological and population parameters. Assuming a flat $\Lambda$CDM model, we measure $H(z)$ at $z\sim1.5$ with 2.4% precision, and achieve a mean precision on $H(z)$ of 2.8% across $0.7

We approach a systematic investigation of the one-loop mass corrections to (super-)string massive higher-spin states. While the imaginary part of the relevant amplitudes are finite, being related to the width of the decay of the states into two lower-mass states at tree level, the real part is generally IR-divergent and needs regularization and renormalization. We mostly focus on states of the first Regge trajectory in the NS-NS sector of Type-II string theories. We explicitly derive a closed-form expression for the integral over the insertion point, relying on properties of elliptic functions and lattice sums. We then regularize the IR divergent integral over the modular parameter of the torus, applying the $i\varepsilon$-prescription in string theory. As a result we compute the desired mass corrections up to level $N = 10$ and analyze their behavior at increasing $N$. Finally, we speculate on the existence of mixing among lower-spin states and conjecture that the one-loop mass matrix be governed by some random matrix theory.