Papers

Helicity in gravity is a multifaceted concept, and several inequivalent definitions exist in the literature. In this work, we reduce the topological Pontryagin and Nieh-Yan terms to a constant time spacelike hypersurface. Remarkably, upon applying the SVT decomposition at the linearized level, we obtain four distinct helicity densities. The helicity density arising from the Nieh-Yan term is termed the spin-1 and spin-2 gravitomagnetic helicity density, depending on whether it originates from vector or tensor modes. Meanwhile, the helicity density arising from the Pontryagin term is termed the spin-1 and spin-2 gravito-current helicity density, according to the corresponding mode contributions. We study the mode and multipole expansions of these helicity functionals and apply them to leading order Newtonian two-body systems, weak field boosted Kerr, a locally defined slowly varying gyratonic pp-wave model, and a linearized gravitational Hopfion.

We construct and analyze a general exact static and spherically symmetric black hole solution in traceless metric-affine bumblebee gravity by considering a vacuum expectation value with temporal and radial components. The temporal component remains constant and the auxiliary geometry is Ricci flat, while Lorentz symmetry breaking is transferred to the physical metric through the metric-affine deformation. After introducing the areal radius and normalizing the Killing time at spatial infinity, the geometry is controlled by a single invariant deformation parameter. The resulting spacetime is asymptotically conical, possesses a regular Killing horizon, and retains the causal structure of the Schwarzschild black hole, with a curvature singularity located at the origin. Initially, we examine its thermodynamic properties, gravitational Doppler effect, and tidal forces. Lorentz symmetry breaking modifies the Hawking temperature and the magnitude of the tidal field, although the characteristic ratio between radial stretching and transverse compression is preserved. The thermodynamic-topology analysis reveals no critical point within the admissible black hole sector. Furthermore, massless scalar perturbations are also investigated through WKB and characteristic time domain solution, showing decaying profiles throughout the sampled parameter range and deformation-dependent quasinormal frequencies. Finally, light deflection and perihelion advance are used to establish stringent Solar System bounds on the invariant deformation, which, at leading order, depends on a combination of the temporal and norm sectors of the bumblebee field.

The increasing precision and complementarity of late-time cosmological observations provide new opportunities to test modified gravity against the observed expansion history of the universe. The combination of DESI DR2 BAO measurements with cosmic chronometers (CC) and independent Type Ia supernova compilations provides a data-driven test of cosmic acceleration. Motivated by this progress, we investigate late-time dark energy dynamics in symmetric teleparallel $f(Q)$ gravity by adopting the power-law form $f(Q)=\beta Q^{m+1}$ and characterizing cosmic evolution through the effective equation of state (EoS) parameter. The model is constrained using CC, DESI DR2 BAO and three independent Type Ia supernova compilations, namely Pantheon+, DES-SN5YR and Union3. The inferred Hubble constant values are mutually consistent, yielding $H_0=67.60^{+1.60}_{-1.66}$, $67.08^{+1.66}_{-1.61}$ and $68.16^{+1.46}_{-1.43}\,\mathrm{km\,s^{-1}\,Mpc^{-1}}$, respectively. Statistically, the proposed $f(Q)$ model yields lower $\chi^2_{\min}$ values and is favored by the AIC for all dataset combinations, whereas the BIC favors $\Lambda$CDM for the CC + DESI DR2 + Pantheon+ and CC + DESI DR2 + DES-SN5YR combinations and indicates no meaningful preference between the two models for the CC + DESI DR2 + Union3 dataset combinations. The reconstructed EoS indicates quintessence-like behavior, while the negative deceleration parameter confirms the current accelerated expansion. The transition from deceleration to acceleration occurs within $0.680\leq z_t\leq0.745$. Higher-order cosmographic parameters and the Statefinder and $Om(z)$ diagnostics consistently support this quintessence-like behavior, with the Statefinder trajectories approaching the $\Lambda$CDM fixed point in the far future. Overall, the power-law $f(Q)$ model provides a viable and competitive description of late-time cosmic acceleration.

We systematically investigate the zoom-whirl periodic orbits of a small compact object orbiting a magnetically charged black hole in $f(R, T)$ gravity coupled with Euler-Heisenberg nonlinear electrodynamics. We evaluate the impact of the magnetic charge $Q_m$ and the Euler-Heisenberg parameter $a$ on the characteristics of the innermost stable circular orbit (ISCO) and the marginally bound orbit (MBO). Particularly, we focus on the precession parameter q and systematically examine how the magnetic charge and other parameters affect the trajectories of periodic orbits. Using the numerical kludge method, we generate gravitational waveforms for these periodic orbits. The results presented in our work demonstrate that the magnetic charge can significantly modify not only the precession parameter but also the orbital trajectories of the periodic orbits. Moreover, changing the magnetic charge $Q_m$ could cause a significant phase shift in the gravitational waveforms, while other parameters exert a relatively weaker influence on the gravitational waves.

In this work we investigate how exotic spinorial topology modifies the propagation of fermionic modes in the Schwarzschild geometry. By incorporating a topological gradient, $\partial_\mu\varphi$, into the Dirac operator through a tetrad deformation, we show that the exotic spinorial sector naturally induces an effective geometric deformation of the Schwarzschild background. The central consequence of this construction is the emergence of a topological impedance surface at $\rtopo=1/q$, which suppresses the radial group velocity of the exotic spinorial modes, yielding a birefringent propagation pattern. Using a spinorial perturbation we discuss the greybody factor and the quasinormal response. The quasinormal spectrum shows the stability of the background metric and the absence of isospectrality for the superpartner potentials.

On a compact connected section ${\cal S}$ of a supersymmetric $M$-horizon the Killing-spinor bilinears give a pointwise identity relating the warp factor $\Delta$, the rotation one-form $h$ and the two spinor norms, with nothing assumed about the norm of the Killing spinor. We derive three consequences of that unreduced identity. First, a single-point rigidity theorem: if $\Delta$ and $h$ vanish at one point of the section, then the flux vanishes identically, ${\cal S}$ is Ricci-flat and the horizon is $\mathbb{R}^{1,1}\times{\cal S}$. A single point replaces the usual global spinorial hypothesis. Second, the ${\rm Spin}(7)$ decomposition of the flux fixes $h$ algebraically and exhibits the invariant flux content of the scalar square $\Delta=4\Phi^2$ known in an adapted gauge, $\Delta=\frac{1}{108}\|w_{\bf 7}\pm\sigma({\cal Y}_{\bf 7})\|^2$. Only the two ${\bf 7}$-summands $w_{\bf 7}$, ${\cal Y}_{\bf 7}$ reach the warp factor, and the square is degenerate rather than definite: it vanishes on the linear subspace $w_{\bf 7}=\mp\sigma({\cal Y}_{\bf 7})$ rather than at the origin, so positivity of $\Delta$ yields no case list. Third, the two combine into a pointwise budget: the single constant of supersymmetry is shared between the deviation from staticity and the ${\rm Spin}(7)$ mismatch of the flux, each bounded by that constant. The same identities characterise the constancy hypothesis, equivalent to $V=-fh$ for the bilinear one-form $V$, which fails on the static branch of known warped $AdS_2$ solutions; they fix a weighted integral of the warp factor; and they reduce the Komar angular momentum of the horizon to a positive bilinear integral. Two no-go statements, for hidden symmetries built from the Killing spinor and for a second isometry from its bilinears, are stated with their hypotheses.

Quantum resonances and black-hole quasinormal modes (QNMs) are described by closely related mathematics: radiative boundary conditions, analytic continuation of Green functions or resolvents, poles on nonphysical sheets, and non-self-adjoint spectral representations. This article does not introduce that equivalence but reconstructs its genealogy. Nuclear resonance theory grew from radioactive decay, reaction cross sections, metastable compound states, and complex energies, whereas black-hole perturbation theory grew from spacetime stability and causal response. We place the two developments on a common chronology, from Sommerfeld's radiation condition and early nuclear-decay theory through Regge–Wheeler perturbations, Vishveshwara's 1968 dissertation and 1970 papers, Press's 1971 quasi-normal terminology, and the independent Aguilar–Balslev–Combes theory of analytic dilation, then follow their later mathematical reunification in scattering-resonance theory. Alongside the chronology, we give a working dictionary relating no-incoming and horizon-ingoing/infinity-outgoing conditions, pole energy and complex frequency, width and damping rate, residues and excitation factors, and nonresonant background with branch-cut and prompt contributions. The aim is to make the cross-disciplinary equivalence operational without flattening its history, and to distinguish mathematical equivalence from historical genealogy.

The No-Scale gravity is a compelling framework to describe particle physics, gravity and cosmology, in which all mass scales are an illusion given by the value of a scalar field $\phi$. This theory, however, falls under the umbrella of more general scalar-tensor theories, which propagate different modes depending on the scalar field, and faces the extensive debate regarding the equivalence between its Jordan and Einstein frame descriptions. In this work we advocate that by excluding the singular point in the transformation between the two frames (e.g., $\phi=0$) we can have the classical equivalence between them. To show the merit of removing this singular point, we argue the Jordan frame makes the symmetries of the model manifest, which creates a suitable playground for the particle-physics model building which we illustrate by showing the emergence of discrete symmetries which leads to a high-quality axion and also naturally incorporate the seesaw mechanism.

The discovery by the James Webb Space Telescope (JWST) of an abundant population of compact little red dots (LRDs) and supermassive black holes at high redshifts poses a severe timing challenge for standard Eddington-limited growth from stellar remnants. In this work, we present a unified hybrid assembly framework in which intermediate-mass seed black holes are formed via hierarchical primordial black hole (PBH) mergers within dense clusters in Hu-Sawicki $f(R)$ gravity, followed by galactic gas accretion. We demonstrate that the screened $f(R)$ fifth force nonlinearly accelerates early seed formation through a quadratic enhancement of the gravitational-wave radiation-capture kernel, while environmental chameleon screening dynamically self-regulates the growth. Because subsequent gas accretion scales multiplicatively with seed mass, the $f(R)$ seed enhancement is preserved throughout the accretion history, drastically reducing the time-averaged Eddington ratios required to assemble $10^{6}\text{-}10^{9}\,M_{\odot}$ LRDs by cosmic dawn. Confronting our active mass functions with JWST data reveals that a small clustered PBH fraction ($f_{\rm PBH} \lesssim 10^{-3}$) under a realistic active galactic nucleus duty cycle ($\delta \approx 10^{-2}$) naturally matches observed LRD space densities at $z \sim 5.5\text{-}6.5$ while remaining fully compliant with LIGO-Virgo-KAGRA limits, with modified gravity naturally driving the high-mass tail. Finally, we show that parameter degeneracies between modified gravity and cluster density can be cleanly broken by combining three multi-messenger diagnostics: remnant spin state signatures, a stochastic GW background cutoff, and a scale-dependent inversion in the PBH spatial correlation function.

Inspired by interaction of gravitational waves, dark matters and dark energy, we study the Einstein scalar field equations with the nonzero cosmological constant for the Bondi-Sachs metrics. We provide the asymptotic expansions under the outgoing radiation condition. Unlike the case of the zero cosmological constant, the asymptotic expansions depend on four additional $\Lambda$-independent functions $B(u, \theta, \phi)$, $\tilde{X}(u, \theta, \phi)$, $\tilde{Y}(u, \theta, \phi)$ and $\tilde{I}(u)$. We show that, under suitable coordinate transformation, we can make $B(u, \theta, \phi)=0$. We prove the peeling property for the Einstein scalar field equations if $\tilde{I}=0$, and derive a loss formula of the Bondi energy-momentum for the nonzero cosmological constant. We remark that, for certain real data from gravitational waves, the loss formula is likely to indicate the loss property of the Bondi energy-momentum.

In this paper, we investigate the late-time accelerated expansion of the Universe in power law $f(Q)$ gravity, where a logarithmic dark energy parametrization is considered: $\omega_{de}(z)=\omega_0+\omega_1\ln(1+z)$. This description gives a smooth deviation from a constant equation of state within the complete range of redshifts. We obtain an analytical expression for the Hubble parameter and we use a Markov Chain Monte Carlo to compare the model with the most recent observational data obtained from Pantheon$^+$ Type Ia supernovae, Baryon Acoustic Oscillation measurements from the second data release (DR2) of the Dark Energy Spectroscopic Instrument, and Cosmic Chronometers. We then perform a statistical comparison between our model and the standard $\Lambda$CDM model using the Akaike Information Criterion and the Bayesian Information Criterion. From our results, we conclude that the use of logarithmic parametrization in the $f(Q)$ gravity model $f(Q)=Q+6\gamma H_0^2\left(\frac{Q}{Q_0}\right)^n$ is a valid and more flexible alternative to standard dark energy models, as it provides a richer phenomenology at low redshifts.

We introduce latent geometry in BFSS/BMN models. Before an emergent geometry evaporates at the geometric transition, large-$d$ Gaussianization encodes its information in the exceptional $N=2$ sector selected by the baby fuzzy sphere, a single active spin-$1/2$ Pauli block. Dimensional reduction, finite-$N$ Gaussianization and exact Molien–Weyl projection transport this encoding to mass-deformed BFSS$_2$. At $N=2$, the same stable BFSS$_2$ oscillator admits inequivalent unitary $\mathbf{H}^2_\theta=\mathbf{EAdS}^2_\theta$ and $\mathbf{dS}^2_\theta$ decodings, realizing spacetime transmutation and the emergence of Lorentzian time.

We study the holographic duality between free vector models and Higher-Spin Gravity in 4-dimensional de Sitter space. On both the bulk and boundary sides, we introduce new reality conditions, which allow us to include odd spins in the bulk, and to extend the duality from type-A to type-B (i.e. from boundary scalars to spinors). The new reality conditions are closely related to a higher-spin-symmetric Hilbert-space norm for the single-particle (super)multiplet in de Sitter space. We construct two alternative viewpoints on the type-A and type-B theories. In one view, the two co-exist in "parallel universes", specifically in even vs. odd antipodal identifications of de Sitter space. In the other view, type-A and type-B are Legendre-transformed descriptions of the same twistor-space theory in Euclidean AdS (this involves the observation that the higher-spin partition function is Legendre-dual to itself). In this way, higher-spin holography reconciles the two-boundary nature of de Sitter space with the one-boundary nature of Euclidean AdS. The supersymmetric theory that unifies type-A and type-B with bulk fermions fails to be consistent under the appropriate reality conditions.

In Einstein gravity, every null geodesic of a non-static Bianchi I spacetime satisfying the null energy condition is incomplete in at least one direction within the Bianchi I region. We prove a stronger directional rigidity theorem: a single null geodesic complete in both affine directions forces staticity if the null curvature is nonnegative along it and, at each time, in one transverse null direction. The spatial metric need not be diagonal, and the expansion rates may have either sign. The proof uses caustic-free null congruences whose conserved spatial covectors define fixed screen hyperplanes. The two curvature conditions admit averaged replacements along the geodesic and, when cosmic time is complete, along comoving worldlines. In a non-static metric, at most four oriented directions are optically saturated; every other complete null geodesic has strictly negative averaged null curvature. Periodic and finite-pulse examples attain this bound with NEC-violating sources and nonpositive total energy density. For finite pulses, we derive bounds on metric excursions from three directional curvature budgets at fixed cosmic duration, and on the mode mixing of a free, massless, minimally coupled test scalar field from the averaged null-energy deficit at fixed affine duration.

Not much. It has been proposed that applying a rational filter to a black hole ringdown gravitational waveform reveals a direct wave component sourced near the event horizon. By solving the Teukolsky equation for a point particle plunging into a Kerr black hole, I show that the maximum amplitude of the waves sourced within the prograde light ring is $\lesssim 10\%$ that of those sourced by the full trajectory no matter if the waves are filtered or not. This agrees with the interpretation of quasinormal modes as waves orbiting the light ring and the direct wave as the power of these modes redistributed in time. Therefore, both quasinormal modes and direct waves are more a probe of the light ring than the near-horizon region. For GW250114, I estimate that the component of the waves sourced within the light ring have a signal-to-noise ratio $\rho \lesssim 1$ measured after the peak of the filtered waves.

Recent results in the study of gravitational scattering amplitudes indicate that some highly-symmetric relativistic systems may exactly conserve a version of the Laplace-Runge-Lenz (LRL) vector in two-body bound states. We make a systematic study, in the context of a generic EFT of long-range interactions due to the exchange of massless mediator particles of spins 0, $\frac{1}{2}$, 1, $\frac{3}{2}$, 2, of the conditions for the conservation of a hidden LRL vector; both classically (no orbital precession) and quantum-mechanically (hydrogen-like degeneracy of bound states). The calculations require several new technical developments including the extension of relativistic post-Minkowskian potential matching to quantum corrections and the incorporation of long-range forces due to the exchange of pairs of massless fermions. We find that while classically the absence of precession is a generic property of a large class of models, including Kaluza-Klein theories, with vector and scalar exchanges, maintaining the degeneracy quantum-mechanically requires a surprising cancellation between gravitons and 6 Majorana gravitinos, hinting at a special role for $\mathcal{N}=6$ supergravity.

Transient noise artifacts, or glitches, in gravitational wave strain data elevate the false alarm rate of astrophysical searches and degrade parameter estimation when overlapping a signal. No method previously identified a glitch's time boundary: existing detection and classification tools flag and label glitches without resolving their extent, forcing subtraction to run over padded windows that cost time and erase signal beyond the glitch itself. We present three boundary identification methods, AMPS (Amplitude-based Multi-glitch Pulse Segmenter), FLARE (Fitness-based Localization And Refinement Extractor), and CRISP (connected-region identification via spectrogram power), paired with three subtraction techniques, adaptive spline fitting, wavelet shrinkage, and their combination, across five glitches from the GravitySpy database spanning Advanced LIGO's first three observing runs. AMPS sets a boundary from a robust amplitude threshold, FLARE from the best fitness of a segmented spline fit, and CRISP from spectrogram power. Injecting a chirp signal on four broadband glitches, the combined technique recovers 95 to 97 percent of the injected signal-to-noise ratio, against roughly 64 percent for wavelet shrinkage alone. CRISP gives the most uniform boundary width across glitches; AMPS and CRISP both identify a boundary in a fraction of a second, two to three orders of magnitude faster than FLARE. For the glitch overlapping GW170817, a low-frequency residual persists under the default boundary, a deliberate tradeoff against removing signal power. Scattered light glitches remain untested and are the primary direction for future work.

Superconducting microwave cavities loaded with radio frequency fields are a powerful tool to search for weak forces or electromagnetic perturbations due to new physics. One source of such signals can be high-frequency gravitational waves emitted from cosmological or unknown astrophysical events. However, large sensitivity improvements are still necessary to reach the parameter space motivated by theoretical models. In this work, we present a formalism to guide the design of such detectors across a broad range of frequencies and signal forms. By incorporating the interdependencies of all relevant parameters and the back-action of the electromagnetic fields on the cavity structure, we describe how figures of merit can be derived for a broad class of relevant experimental setups. Using a two-dimensional model, we demonstrate this formalism and present examples for optimized cavity geometries. We find that the choice of geometry alone can increase the signal-to-noise power ratio by an order of magnitude compared to an existing prototype of the same size. We also show that different physics goals lead to different optimal cavities, thus proving the need to consider such figures of merit at an early stage when designing a new detector.

This work investigates the original Penrose process (PP), as well as black hole (BH) thermodynamics, within the framework of conformal Weyl gravity. The theory is characterized by the dimensionful constants $\gamma$, which encodes the asymptotic rotational curvature of galactic rotation curves in an otherwise asymptotically flat spacetime, and $\kappa$, which is associated with the cosmological background constant $\Lambda$. We determine the locations of the event horizon and the extreme configurations for rotating BHs in this theory, and we provide both perturbative and exact expressions for the event horizon radius. The geodesic equations are restricted to the equatorial plane, and the corresponding dynamics, including energy extraction processes, are studied exclusively in this plane. As the principal results, we examine the feasibility and efficiency of the original PP, analyze BH deceleration mechanisms, and test the validity of the four laws of BH thermodynamics in the context of conformal Weyl gravity.

We investigate timelike bound motion, resonant periodic orbits, and their gravitational-wave signatures in the rotating Konoplya-Zhidenko (KZ) black hole spacetime. Using the separability of the Hamilton-Jacobi equation, we parameterize eccentric and inclined bound orbits by $(p,e,z_1)$, derive the corresponding constants of motion $(E,L_z,Q)$, and use the orbital frequencies to identify resonant configurations. We study a range of resonances, including radial-polar resonances of inclined orbits and radial-azimuthal resonances of equatorial eccentric orbits. We further construct physically scaled quadrupole-kludge waveforms for representative equatorial resonant orbits and analyze their frequency-domain characteristics. Our results show that the KZ deformation shifts the resonance locations and modifies both the orbital trajectories and the resulting gravitational-wave signals. The corresponding characteristic strain lies predominantly in the millihertz band, placing these signals in the frequency range relevant to space-based gravitational wave detectors.

We develop an entropy-stable and physical-constraint-preserving discontinuous Galerkin spectral element method for symmetry-reduced general-relativistic hydrodynamics on prescribed stationary spacetimes. Using a local orthonormal transformation, the fluid variables are expressed in a form for which the relativistic hydrodynamic algebra and the admissible set are independent of the spatial metric, while the spacetime geometry enters through stationary coefficients. This separation allows entropy-conservative special-relativistic fluxes to be combined with a compatible discretization of the geometric source terms. On affine tensor-product meshes, the resulting DGSEM is conservative and satisfies a semidiscrete entropy inequality, while the transformed variables provide a convex framework for physical-constraint preservation. For practical stabilization, we use a geometry-only causal speed that is sufficient for both classical local Lax–Friedrichs entropy dissipation and the physical-constraint-preserving Lax–Friedrichs splitting. The fully discrete method combines this stabilization with SSP Runge–Kutta time stepping, oscillation elimination, and conservative local-orthonormal-state scaling. Numerical experiments cover smooth and strongly shocked special-relativistic flows, an axisymmetric jet, stationary Michel accretion, Schwarzschild Bondi–Hoyle flow, and four Kerr accretion cases. The results demonstrate the designed high-order accuracy in smooth regimes and robust performance for demanding relativistic flows on curved stationary backgrounds.

Inspired by holographic dark energy models, we extend the analysis performed in Ref.\cite{RGPC} taking into account Yukawa deformations on the different energy density (HDE) profiles. The profiles we have explored are: the Bekenstein-Hawking HDE, the Moradpour energy density, the Standard Renyi HDE and the Mixed Energy Density. With the help of an inhomogeneous Equation of State of the form $p_{r}(r)=\omega _{r}\left( r\right) \rho (r)$, we have considered Zero Tidal Forces. Differently from the original case, only a particular case of the family of the Bekenstein-Hawking HDE profiles distorted by the Yukawa term has developed a divergent $\omega _{r}\left( r\right) $ for $r\rightarrow \infty $. To cure such a divergence we have introduced a modification at large distances in order to have a finite result. This means that the Zero Tidal Forces can be imposed in a very large but limited region of the spacetime. Such modification did not change the behavior of the Equation of State close to the throat. For every proposal we have computed the components of the Stress-Energy Tensor. What we have found is that the Yukawa-Bekenstein-Hawking HDE is the only positive profile, while the Yukawa-Moradpour and the Yukawa-Renyi have a limited region where the energy density is positive. The remaining Yukawa-Mixed Energy Density is always negative. This means that the Yukawa distortion introduces a kind of negative energy density.

The motion of a spinning test particle in a curved spacetime is governed by the Mathisson–Papapetrou–Dixon (MPD) equations and deviates from geodesic motion already at first order in the spin. While essentially all existing studies truncate the dynamics at linear order in the spin, we present an exact, nonperturbative treatment of planar motion in Schwarzschild spacetime under the Tulczyjew–Dixon spin supplementary condition: eliminating the four-velocity recasts the MPD system into a closed algebraic form and reduces the radial motion to an effective-potential problem, with no expansion in the spin at any stage. This exact framework uncovers qualitative features that are absent from—and in fact unattainable within—the linearized description. Most notably, for sufficiently large spin the effective potential develops a double root at a characteristic radius determined solely by the particle mass and spin, marking an impenetrable spin wall of purely spin origin; beyond a critical spin the wall lies outside the event horizon and shields it from generic infalling particles. Moreover, the wall is a filter for particle: only orbits with a specific combinations of spin, angular momentum and energy can penetrate it, all others being reflected before reaching the horizon. In addition, the innermost stable circular orbit, which in linear treatments merely shifts continuously with spin, is obtained in closed form in the weak-field limit and is shown to cease to exist at sufficiently large spin. We further compute the spin correction to the perihelion precession in the weak-field limit and verify that all results reduce to the standard ones at vanishing spin. The spin wall and its filtering rule are genuine nonperturbative phenomena, invisible to any finite-order expansion in the spin, with potential observational signatures in accretion flows around compact objects.

Compactified spectral discretisations may yield stable negative-imaginary-axis (NIA) eigenvalue ladders, but finite-matrix convergence does not establish quasinormal poles. For axial Schwarzschild perturbations, ingoing–outgoing factorisation leaves an unwanted horizon solution behaving as $t^{4\alpha}$ at $\Omega=-i\alpha$, and a $C^\infty$-flat unwanted infinity solution. Thus endpoint $C^k$ regularity is nonselective for $4\alpha>k$, so the $C^2$ continuum problem cannot have a discrete NIA spectrum over $\alpha\simeq15$–32. Exact Chebyshev-grid formulas give roots-grid maximum radius $O(n^{2p})$ for $x\sim C(1-y)^{-p}$, explaining C1, $x=2/(1-y)$, versus C2, $x=4/(1-y)^2$. Arbitrary-precision pencils nevertheless reveal a reproducible 68-point C1 ladder, while C2 reorganises it. Both physical lateral Jost determinants remain stably nonzero at every C1 frequency. A 0.05-spaced on-cut scan finds no zero, and refined argument-principle calculations give zero winding in both continuation strips. This rejects all 68 candidates, although the mesh and strip evidence is not interval-certified. Same-damping controls recover Schwarzschild QNMs $n=60,100,130$, with $|\widehat{\mathcal D}|=10^{-48}$–$10^{-56}$. The ladder has surface-gravity quarter spacing, follows the parameter-free Casals–Ottewill branch-cut-strength phase, and pairs with damping projections of QNMs $n=62,\ldots,129$. At its first member, a finite-frequency calculation finds a branch-strength zero at $\alpha_q=15.07832396512359$, between the asymptotic prediction and the C1 root, supporting, but not proving, sequence-wide cut-phase locking. Thus accurate finite-pencil eigenvalues can fail the invariant Jost/Evans pole criterion. Whether representation-dependent nodes with Keldysh weights converge collectively to the Schwarzschild cut response and Price tail remains open.

We study slowly rotating Bose–Einstein condensate (BEC) dark stars by solving the Tolman–Oppenheimer–Volkoff, Hartle dipole, and Postnikov–Hinderer equations together for a polytropic equation of state with a Lee–Huang–Yang correction of strength $\zeta$~\citep{Panotopoulos2026}. A continuous scan of $\zeta$ from 0 to 1.5 shows the mean-field-to-corrected transition is smooth, with no hidden structure at intermediate values. Scanning the underlying boson parameters $(m,a_s)$ more broadly, we find that a $2\,M_\odot$ maximum-mass bound and a GW170817-like tidal bound $\Lambda_{1.4}\lesssim800$ cannot be satisfied simultaneously anywhere in this equation-of-state class. The $I$-Love universal relation holds to $0.13\%$ across twelve $(m,a_s,\zeta)$ models, and the $\zeta=0$ and $\zeta=1$ sequences sit on opposite sides of the master curve by a consistent, non-random offset. Applied without modification to realistic nuclear matter (SLy, APR4), the same solver reproduces published maximum masses to within $1\%$; applied to self-bound MIT-bag quark matter it gives the expected mass–radius shape; and once extended to a two-fluid baryon-plus-dark-matter formalism, it shows that the maximum mass of a hybrid star is not a monotonic function of the central dark-matter fraction. Pooling $I$-Love sequences across nuclear, hybrid, and BEC dark-star models, we find they collapse onto a single curve to within about $5\%$, while self-bound quark stars sit far off it, departing by up to $90\%$.

This paper introduces formalism, based on worldline effective field theory, which allows one to systematically calculate the gravitational self-force on a compact object immersed in an environment with non-vanishing stress energy. Using the closed time path integral we present a universal effective action that can be used to calculate the equations of motion of a compact object due to its interaction with the environment to any order in the relevant expansion parameters, the relative importance of which depends upon the choice of environment. We show that the leading order equations of motion can be universally written in terms of the retarded two-point function of the stress-energy tensor for the environment. The resulting action can be used to calculate both dissipative (dynamical friction) and conservative forces in a completely relativistic fashion. We demonstrate the utility of the result by calculating the dissipative force due to dust, an inviscid fluid, and a coherent field. Our results agree with those previously derived in the literature. We furthermore show that the famous “Coulomb Log" found by Chandrasekhar should be interpreted as a renormalization group log due to a UV divergence that renormalizes the dissipative part of the in-in action. We then prove that this log is universal in the Newtonian limit in that its value is universal, for a generic class of environments and trajectories. This log is the leading log in an RG flow in the dissipative action that has yet to be explored.

The existence of quantum gravity is the most important question in theoretical physics. Besides the theoretical development in this direction, looking for its low-energy consequences can provide clues. However, besides availability, it is crucial to ensure that what is observed uniquely comes from quantum gravity and not from other forces in the environment. What is the unique feature of gravity? The spin-$2$ nature of its propagator. In this Letter, we calculate what the unique feature of the spin-$2$ graviton is in the interaction of two spin-$\frac{1}{2}$ particles. This unique feature shows itself in intertwining the spin and momentum of two particles simultaneously as a dipole-dipole interaction. This cannot happen for any spin-$0$ or spin-$1$ propagator, at least at leading order, which scales as $\frac{1}{r^3}$ in real space. We re-calculate the results using an independent approach, i.e., the Foldy-Wouthuysen transformation, and reach the same results. Due to simultaneous coupling of both particles' spins and momenta, a four-partite entanglement framework is suggested to observe this effect.

Since the first exact solutions of General Relativity (GR) were obtained, it became clear that the theory predicts a new class of compact objects: black holes. The Hawking–Penrose singularity theorems show that, under appropriate assumptions, gravitational collapse in GR leads to singular behavior. Motivated by the expectation that such regimes require physics beyond classical GR, effective approaches inspired by Loop Quantum Cosmology (LQC) and braneworld scenarios introduce high-density corrections. In this work we consider the static exterior geometry introduced by Gao, Lu, Shen, and Faraoni, associated with a comoving interior model in which the singularity is avoided through a sequence of collapse and bounce phases. Using the Newman–Janis algorithm in the Azreg-Aïnou formulation, we construct a stationary rotating exterior extension of this geometry. The resulting line element describes a stationary axisymmetric rotating spacetime whose horizon geometry, angular velocity, surface gravity, and Hawking temperature recover the Kerr and Schwarzschild limits when the quantum/braneworld correction becomes negligible ($l\to 0$). We further analyze the thermal response at fixed rotational state-space parameter, identify Davies-type singular points, and formulate an extended thermodynamic state-space relation.

Many modified-gravity frameworks employ non-Riemannian connection degrees of freedom, including torsion and nonmetricity. In Einstein-Cartan-type theories, torsion is associated with spin density, while more general metric-affine frameworks can be investigated through phenomenological searches for in-matter torsion and nonmetricity backgrounds. This work applies an effective field theory approach to characterize general couplings of electron and neutron operators to spacetime torsion and nonmetricity up to mass dimension six, predicting novel neutron-polarization signatures in the presence of an electron background. Neutron spin-rotation data from a polarized-electron ensemble inside a compensated ferrimagnet are used to constrain for the first time axially symmetric, direction-dependent in-matter torsion and nonmetricity combinations.

We present a new family of exact solutions representing accelerating, rotating, point particle and black hole solutions in three-dimensional Einstein gravity. We investigate their geometric properties and the global embedding in three dimensional anti-de Sitter space. Our results extend the catalogue of exact solutions in three-dimensional Einstein gravity and provide a useful setting for the study of black hole thermodynamics, asymptotic symmetries, and holography.