We investigate whether the hidden zeros and associated factorizations found for massless color-ordered amplitudes persist under massive deformations. Using the kinematic mesh construction, we show that hidden zeros survive only for symmetry-controlled mass generation. For massive $\mathrm{Tr}{\mathrm{\Phi }}^3$ with a uniform mass, the zeros and their factorization patterns are inherited after a massive shift of planar variables, and an analogous statement holds for Kaluza-Klein reductions where the relevant nonplanar variables are modified by conserved mode numbers. For the nonlinear sigma model (NLSM), a naive pion mass term generically spoils hidden zeros, while a spurion induced potential restores them. This allows factorization near zeros, including odd point channels described by an appropriately mass deformed NLSM + ${\varphi }^3$ theory, and leads to a hidden zero based on-shell recursion for massive NLSM amplitudes. For spin-one, a simple massive Yang-Mills theory fails to exhibit hidden zeros, while spontaneously broken gauge theories preserve them.

We show that a three-dimensional Manin gauge theory with gauge group $\mathrm{SL}(2;\mathbb{R})$ (i.e., Yang-Mills theory, the third-way theory, or the imaginary third-way theory) minimally coupled to Einstein gravity admits a dual interpretation as Einstein gravity with an exotic coupling to a Manin gauge theory, where the roles of dreibein/spin connection and field strength/gauge potential are interchanged. The dual, or ersatz, gravitational metric ${\widehat{g}}_{\mu \nu }\sim \mathrm{tr}((\star F{)}_{\mu }(\star F{)}_{\nu })$ is a classical double copy of the gauge-field strength $F_{\mu \nu }$ (as opposed to the usual double copy of the gauge potential $A_{\mu }$). If matter exclusively couples to $\widehat{g}$ (for example, in a gravitational decoupling limit), then one can formulate black-hole thermodynamics with regard to the ersatz metric. In particular, a black-hole solution for the ersatz metric ${\widehat{g}}_{\mu \nu }$ (made of Yang-Mills fields) radiates ersatz Hawking radiation and obeys the laws of black-hole thermodynamics.

The interaction of quantum fields with fractal and self-similar geometries encompasses multiple distinct physical regimes, including spectral geometry on intrinsic fractals, macroscopic self-similar Casimir configurations, and bounded Euclidean cavities with fractal boundaries. While the thermal equations of state and spectral asymptotics for these systems are well established, a cohesive treatment of the vacuum trace frequently conflates rigorous mathematical bounds with phenomenological models. In this manuscript, we systematically decouple these regimes and advance a unified effective framework combining the rigorous thermal trace of fractal radiation with a zero-temperature integrated vacuum trace for platelike self-similar geometries. We demonstrate that for systems governed by a scale-dependent Casimir coefficient $C(d_s,\ln (d/{\ell }_{*}))$, the anisotropic stress-energy tensor produces an integrated vacuum trace proportional to its logarithmic running, ${\partial }_{\ln d}C$. We strictly differentiate this effective macroscopic backreaction from first-principles local trace anomalies on genuine fractal boundaries. Finally, we analyze finite-level ($n$) prefractal realizations, establishing the analytical prerequisites necessary to transition this effective formalism into a quantitatively predictive electromagnetic theory amenable to experimental verification.

In this work, we study nonradial perturbations of AdS bubbles and their tidal Love numbers (TLNs). The odd- and even-parity TLNs are computed up to $l=6$ in the limit $k\to \infty$. The odd-parity TLNs are found to be negative, while the even-parity TLNs are positive for ${\upsilon }_s^2=-1$. As $l$ increases, the tidal Love numbers approach zero. The TLNs of the even-parity sector up to order $l=41$ are also calculated over the entire parameter space of $k$, from 0 to $\infty$. We find that in the region where $p/\sigma >0$, an increasing number of TLNs become negative as $l$ increases. For $l=41$, the highest order we have examined, the TLNs are negative everywhere except in a narrow region very close to the zero of $p/\sigma$, which agrees well with the instability criterion in the eikonal limit for self-gravitating membranes proposed by Yang et al. [Phys. Rev. Lett. 130, 011402 (2023)].

Massive bosonic fields can trigger superradiant instabilities in rotating astrophysical black holes leading to gaps in their mass-spin distribution. For spin-2 fields, the instability timescale is orders of magnitude shorter than for any other superradiant mode, thereby yielding much stronger constraints. We consider a tower of ultralight spin-2 fields arising from a warped compactification of a single extra dimension and translate superradiant constraints on their masses into constraints on the warping. As a concrete scenario we consider the 2-brane Randall-Sundrum model and find constraints on the size of the extra dimension and the curvature of ${\mathrm{AdS}}_5$. We discuss the implications of these bounds for strongly warped throats and D-brane uplifts commonly used in attempts to realize metastable de Sitter vacua in string theory.

We establish the dynamical instability of a static, spherically symmetric, and infinitesimally thin shell in general relativity. The shell is made up of a perfect fluid with a barotropic equation of state, and it produces a Schwarzschild spacetime in its exterior and a Minkowski spacetime in its interior. We introduce a linear perturbation of the matter and spacetime, decompose it in spherical harmonics, and compute the shell’s spectrum of quasinormal modes. We reveal the existence of two modes with a purely imaginary frequency, one negative (which describes stable oscillations), the other positive (which describes an exponential growth); these modes occur for all sampled values of the shell’s compactness and adiabatic index, and all sampled values of the multipolar order $\ell \ge 2$, in the even-parity sector of the perturbation. All other quasinormal modes describe damped oscillations and do not contribute to the instability. This study complements a recent analysis by Yang, Bonga, and Pen [Phys. Rev. Lett. 130, 011402 (2023)], which also concluded in a dynamical instability, but was limited by an eikonal approximation to small angular scales ($\ell \gg 1$); our treatment applies to all angular scales. The eigenvalue problem for the mode frequencies is formulated by introducing a perturbation of Minkowski spacetime inside the shell, a perturbation of Schwarzschild spacetime outside the shell, and a perturbation of the shell matter. The metric perturbations are governed by the Einstein field equations, and they are matched across the shell with the help of Israel’s junction conditions. The matter perturbation is governed by the equations of fluid mechanics, and it produces a source term in the junction conditions. All calculations are carried out in full general relativity, but we also examine a nonrelativistic formulation of the problem; we show that a Newtonian shell also is necessarily unstable to a time-dependent perturbation. Our conclusion suggests that a compact object that features a thin shell at its surface will be dynamically unstable; this makes it nonviable as a model of black-hole mimicker.

We clarify the relationship between rotation and the energy condition for stationary rotating wormhole solutions of the Einstein equations coupled to a phantom field in five-dimensional spacetime with equal angular momenta, particularly with large asymmetry between the two sides. Setting equal angular momenta about two independent axes leads to a spatial section that is a homogeneous squashed 3-sphere at a constant radial coordinate. It was shown by Dzhunushaliev et al. that the violation of the null energy condition can become arbitrarily small due to rotation. We find that the degree of violation of the null energy condition is essentially determined by the angular momentum and shows little dependence on asymmetry, that is, the mass difference between the two asymptotic regions. We also discuss the relation between the wormhole spacetime and the Myers-Perry black hole. We find that the geometry asymptotes to the extremal Myers-Perry spacetime in the limit of large angular momentum, while the nonextremal black hole geometry cannot be reproduced in any limit.

Superradiant instabilities of rotating black holes can give rise to long-lived bosonic clouds, offering natural laboratories to probe ultralight particles across a wide range of parameter space. The presence of a companion can dramatically impact both the cloud’s evolution and the binary’s orbital dynamics, generating a trail of feedback effects that require detailed modeling. Using a worldline effective field theory approach, we develop a systematic framework for binaries on generic (eccentric and inclined) orbits, capturing both resonant and nonresonant transitions without relying solely on balance laws. We demonstrate the existence of “corotating” floating orbits that can deplete the cloud prior to entering the detector’s band, triggering eccentricity growth towards a sequence of fixed points. Likewise, we show that “counterrotating” orbits can also deplete the cloud, driving (unbounded) growth of eccentricity. Furthermore, we uncover novel features tied to orbital inclination. Depending on the mass ratio, equatorial orbits can become unstable, and fixed points may arise not only for aligned or antialigned configurations but, strikingly, also at intermediate inclinations. We derive flow equations governing spin-orbit misalignment and eccentricity and identify distinctive signatures that can reveal the presence of boson clouds in the binary’s history, as well as key features of possible in-band transitions. These results refine and extend earlier work, yielding a more faithful description of the imprints of ultralight particles in gravitational-wave signals from binary black holes, signatures that are within reach of future detectors such as LISA, Cosmic Explorer, and the Einstein Telescope.

Extreme mass-ratio inspirals (EMRIs) provide a uniquely precise probe of strong-field gravity, where small deviations from vacuum Kerr geometry can accumulate over many orbital cycles. In realistic astrophysical settings, black holes are embedded in surrounding dark and baryonic matter whose presence and motion can perturb the spacetime. A systematic semianalytic framework incorporating the rotation of the environment itself into a black hole geometry, and propagating its effects consistently into conserved quantities and epicyclic observables, has not been explored exhaustively, limiting consistent assessments of environmental effects on precision observables. In this work, we construct a slowly rotating black hole spacetime embedded in an anisotropic matter distribution and explicitly include the angular velocity of the surrounding medium within a controlled slow-rotation expansion. We demonstrate that the environment’s velocity field induces corrections to the metric coefficients that propagate into modifications of conserved quantities governing geodesics. We also derive semianalytic shifts in the innermost stable circular orbit, light-ring location, and radial and vertical epicyclic frequencies, showing that environmental rotation produces systematic and, in certain regimes, qualitatively distinct behavior relative to static configurations. Consequently, we explicitly show that the environment’s nature and motion shift the positions of the epicyclic resonances. The formalism applies to generic anisotropic matter profiles and is not restricted to the specific halo model adopted for numerical illustration. These results establish a direct and quantitatively controlled link between environmental rotation and strong-field orbital observables, enabling consistent incorporation of rotating matter environments into precision EMRI modeling.

We calculate the first-order (in the mass ratio) metric perturbation produced by a small body on an eccentric, precessing bound orbit about a Kerr black hole. We reconstruct the metric perturbation from the maximal spin-weight Weyl scalars, ${\psi }_0$ and ${\psi }_4$, using four different methods. The first two follow the work of Chrzanowski, Cohen, Kegeles, and Wald and reconstruct the metric perturbation from either ${\psi }_0$ or ${\psi }_4$, leading to perturbations in the ingoing or outgoing radiation gauges. The other two methods build upon the work of Aksteiner, Andersson, and Bäckdahl and reconstruct the metric perturbation from both ${\psi }_0$ and ${\psi }_4$. We compare the local and asymptotic behaviors of the metric across different gauges. We also calculate the generalized redshift invariant along eccentric, precessing orbits in Kerr spacetime for the first time and make the numerical methods employed in these calculations openly available through the python library pybhpt. Building off recent work by Lewis et al., we also relate our redshift data to the Hamiltonian of the system. Combining our numerical data with this Hamiltonian formulation provides a method for generating waveforms that include postadiabatic conservative effects and acts as a useful bridge between results in self-force, effective-one-body, and post-Newtonian theory.

A key tenet of general relativity is the dynamical nature of spacetime, ideally represented as an initial value problem. Here we explore the variational formulation of classical Einstein-Hilbert gravity as an initial value problem by constructing its Schwinger-Keldysh-Galley (SKG) action, including a careful treatment of boundary terms. The construction is based on a doubling of degrees of freedom and is independent of a foliation. The action naturally decomposes into a bulk term furnishing Einstein’s equations and a boundary term, which is related to conserved quantities, such as the Komar mass. We find that since only trivial connecting conditions must be specified on boundaries, the action principle for gravity as an initial value problem is rendered well-posed in the variational sense, without the need to add additional boundary terms. The SKG approach to gravity offers a novel and complementary avenue to solve for the metric of spacetime from the action, bypassing the governing equations.

Synergies between self-force theory and other approaches to the gravitational two-body problem have traditionally relied on calculations of gauge-invariant observables as functions of orbital frequencies. However, in self-force theory, one can also define a complete set of constants of motion: energy, azimuthal angular momentum, and radial and polar actions. Here, we outline how directly utilizing these constants allows for more straightforward comparisons and hybridizations across the parameter space, as well as more streamlined waveform generation through flux-balance laws. Restricting to the case of eccentric, nonspinning binaries and first order in self-force, we compute the constants of motion and the corrections to fundamental frequencies numerically as well as analytically (to 9PN in a post-Newtonian expansion), establishing consistency with the highest-order (4PN) results available from post-Newtonian theory. We also apply the results to identify the perturbed locations of special curves in the parameter space: circular orbits and the separatrix between bound and plunging orbits.

We develop a comprehensive thermodynamic description for a zero-temperature boson gas in a fixed, classical curved spacetime, integrating energy conservation with information-theoretic principles. Using the hydrodynamic Madelung representation within the Arnowitt-Deser-Misner formalism, we establish two fundamental relationships: an energy balance equation representing the first law of thermodynamics from a spacetime perspective, and an information-theoretic constraint connecting Fisher entropy to the dynamical evolution of the boson density. This formulation clearly separates energy transport from the conservation of quantum information encoded in the boson gas, while revealing how such information is preserved in curved backgrounds. The introduction of a stochastic velocity provides a bridge between quantum potential effects and underlying spacetime fluctuations. We demonstrate the consistency of our framework through detailed analyses of quantum systems in both Minkowski and Schwarzschild spacetimes. This work provides a unified foundation for studying relativistic bosonic systems, with direct relevance to boson stars and scalar field dark matter models.

The ringdown stage of a binary black-hole merger provides a clean probe of strong-field gravity, as it can be modeled with minimal assumptions. The quasi–normal-mode frequencies encode the mass and spin of the Kerr black hole remnant, while the mode excitation depends on the progenitor binary. In this paper, we implement a recently developed amplitude model that captures spin precession in a simulation-based inference pipeline that specifically targets ringdown signals. We present a reanalysis of GW190521—a short-duration, merger-dominated event with conflicting interpretations. Spin-aligned and precessing analyses at two ringdown start times show that precession induces modest but systematic shifts in inferred parameters and subdominant mode amplitudes, although such ringdown-only analyses provide no strong evidence for precession. Our results demonstrate the feasibility of physics-informed precessing ringdown modeling, paving the way for the identification of spin precession in gravitational-wave events using solely their ringdown stages, where waveform systematics are expected to be substantially less prominent.

We revisit scalarized black holes in Einstein-scalar-Gauss-Bonnet gravity and analyze the thermodynamic phase transition between the Schwarzschild solution of general relativity and scalarized black holes. Restricting to spherically symmetric configurations, we investigate several classes of scalar-Gauss-Bonnet coupling functions. For the simplest quadratic coupling that triggers spontaneous scalarization, the scalarized solutions are thermodynamically disfavored and no phase transition occurs. For an exponential coupling, the phase structure depends strongly on the coupling parameter, allowing for the absence of a transition, a continuous second-order transition, or a discontinuous first-order transition. For couplings leading to purely nonlinear scalarization, we find either a first-order transition or no transition. These results reveal a rich phase structure of scalarized black holes controlled by the scalar-Gauss-Bonnet coupling.

Recent measurements of baryon acoustic oscillations (BAOs) from the Dark Energy Spectroscopic Instrument (DESI) have been interpreted to suggest that dark energy may be evolving. In this work, we examine how prior choices affect such conclusions. Specifically, we study the biases introduced by the customary use of uniform priors on the Chevallier-Polarski-Linder (CPL) parameters, $w_0$ and $w_a$, when assessing evidence for evolving dark energy. To do so, we construct theory-informed priors on $(w_0,w_a)$ using a normalizing flow (NF), trained on two representative quintessence models, which learns the distribution of these parameters conditional on the underlying $\mathrm{\Lambda }$ cold dark matter ($\mathrm{\Lambda }\mathrm{CDM}$) parameters. In the combined Planck $\mathrm{CMB}+\mathrm{DESI}$ BAO analysis, we find that the apparent tension with a cosmological constant in the CPL framework can be reduced from $\sim 3.1\sigma$ to $\sim 1.3\sigma$ once theory-informed priors are applied, rendering the result effectively consistent with $\mathrm{\Lambda }\mathrm{CDM}$. For completeness, we also analyze combinations that include Type Ia supernova data, showing similar shifts toward the $\mathrm{\Lambda }\mathrm{CDM}$ limit. Taken together, the observed sensitivity to prior choices in these analyses arises because uniform priors—often mischaracterized as “uninformative”—can actually bias inferences toward unphysical parameter regions. Consequently, our results underscore the importance of adopting physically motivated priors to ensure robust cosmological inferences, especially when evaluating new hypotheses with only marginal statistical support. Lastly, our NF-based framework achieves these results by postprocessing existing MCMC chains, requiring $\approx 1\mathrm{h}$ of additional CPU compute time on top of the base analysis—a dramatic speedup over direct model sampling that highlights the scalability of this approach for testing diverse theoretical models.

We investigate the viability of Tsallis holographic dark energy (THDE) models, focusing on the role of the infrared (IR) cutoff in the growth of cosmic structures. Considering two commonly used choices of the cutoff, the particle horizon, and the future event horizon, we analyze the evolution of linear matter perturbations and compute the growth factor, growth rate, and the observable $f{\sigma }_8(z)$. These predictions are compared with observational data from redshift-space distortion measurements. We find that the growth history is highly sensitive to the choice of IR cutoff. Models based on the future event horizon are consistent with observational data and can provide a fit comparable to, or slightly better than, the $\mathrm{\Lambda }$ cold dark matter model for suitable values of the Tsallis parameter $\delta$. In contrast, models constructed using the particle horizon generally fail to reproduce the observed growth of structure. These results demonstrate that the viability of THDE models depends crucially on the choice of IR cutoff and highlights the importance of structure formation as a stringent test of generalized holographic dark energy scenarios.

Large-scale $B$-mode polarization of the cosmic microwave background (CMB) is a prime target for current and future experiments in search of primordial gravitational waves. With increasingly sensitive instruments being deployed, secondary $B$-modes induced by the weak gravitational lensing of CMB photons are becoming an important limitation and need to be removed, a process known as delensing. In this work, we combine internally reconstructed CMB lensing maps from the Atacama Cosmology Telescope (ACT) data release 6 (DR6) with galaxy samples from unWISE and a map of the cosmic infrared background (CIB) fluctuations from Planck to produce a well-correlated tracer of the CMB lensing field. Our coadded tracer, shown to be 55%–85% correlated with the true lensing convergence at multipoles $L\le 2000$, is then convolved with ACT DR6 $E$-mode polarization to yield a template of the lensing $B$-modes. We assess its performance on a wide range of scales by using it to delens ACT DR6 and Planck $B$-modes over 23% of the sky, removing around 39% of the lensing power at $100\le l\le 1500$ and 47% at $30\le l\le 300$, respectively. Our template achieves the highest delensing efficiency to date and will be useful for the analysis of early polarization maps from the Simons Observatory. We finally outline prospects for further improvements by including additional large-scale structure tracers from upcoming cosmological surveys.

Multifield models of inflation typically assume that interactions between particles are weak and can be treated perturbatively. Strongly coupled models provide an intriguing alternative and may offer novel inflationary phenomenology. In this work, we study the “unparticle” scenario, where the inflaton is weakly mixed with a strongly coupled sector, specified by a (gapless) conformal field theory. For certain choices of the conformal scaling dimension $\mathrm{\Delta }$, the exchange of unparticles leads to distinctive non-Gaussian features in the primordial curvature distribution, including bispectra with enhanced squeezed limits and oscillations close to the equilateral regime. Efficiently analyzing these models using cosmic microwave background (CMB) data is a challenge since (a) they are defined over a wide range of $\mathrm{\Delta }$, (b) the novel phenomenology is not restricted to squeezed limits, (c) the bispectra are nonfactorizable in momenta, and (d) the signatures are often highly degenerate with single-field self-interactions. Here, we overcome these limitations using a library of tools, including recently developed neural-network factorization schemes, principal component analyses (with carefully chosen bases), and optimal CMB estimators. Our combined pipeline condenses 161 nonseparable unparticle bispectra into just 7 factorizable forms, with negligible loss of signal-to-noise ratio. We apply the model to the latest temperature and polarization data from Planck, asking two key questions: (1) Can we detect unparticles? (2) Can we distinguish between unparticle bispectra and single-field self-interactions? Across $1\le \mathrm{\Delta }\le 9$, we find a maximal signal-to-noise ratio of $1.2\sigma$ (or $1.7\sigma$ in an analysis marginalized over self-interactions), implying no evidence for new physics. We also place the first CMB constraints on the modified consistency-condition-satisfying orthogonal bispectrum typically used in galaxy survey analyses with $f_{\mathrm{NL}}^{{\mathrm{orth}}^{*}}=-12\pm 12$. While many unparticle models are very degenerate with the single-field shapes (and highly correlated among themselves), certain values of $\mathrm{\Delta }$ (close to half-integers) have very different shapes, offering an intriguing discovery channel for future experiments. The methods developed herein can be directly applied to other classes of strongly coupled sectors (and beyond), motivating the exploration of models beyond the standard weakly coupled paradigm.

In this paper, we investigate a quintessence field with an exponential potential motivated by the suggestion of time-varying dark energy from the DESI galaxy survey. Assuming a kination epoch in the early Universe, we analytically derive constraints on initial conditions that are consistent with big bang nucleosynthesis and the current dark energy density. Compared to the severe 120-digit fine-tuning required for dark energy to be a cosmological constant, our result suggests that the degree of fine-tuning is naturally relaxed by dozens of orders of magnitude. Furthermore, we discuss the method for testing this model through future observations of the gravitational wave background.