arXiv subjects

Yu-Xiao Liu

Publications and source records attributed to Yu-Xiao Liu.

At least 19 recordsLinked to original sources

arXiv2026

Milky Way Structure from Double White Dwarf Gravitational-Wave Sources

The millihertz gravitational-wave sky will be dominated by $\sim10^{4}$--$10^{7}$ resolved double white dwarf binaries in the Milky Way, whose three-dimensional spatial distribution traces the Galaxy's structural parameters. We present \textsc{Galena}, a hierarchical Bayesian pipeline that recovers these parameters from a double white dwarf catalogue through an inhomogeneous Poisson-process likelihood. Each source's $3\times3$ Galactic position covariance is computed from the waveform Fisher information matrix and propagated analytically through a $3\times5$ Jacobian; the resulting measurement-error convolution is factored into a pre-computed sparse weight matrix, rendering the nested-sampling inference tractable. Applied to GBSIEVER-reported LISA Data Challenge sources ($N=2151$ after quality cuts), \textsc{Galena} recovers the disk scale length $R_d=2175^{+51}_{-52}$~pc and scale height $z_d=282^{+7}_{-7}$~pc, consistent with a canonical thin disk, together with the bulge fraction $A=0.187^{+0.011}_{-0.012}$ and bulge scale radius $R_b=773^{+26}_{-25}$~pc; the bulge fraction, now recovered much closer to the literature value of $0.25$ than in our earlier exact-position fit, is measured at $\sim6\%$ statistical precision. An independent particle-swarm optimisation of the same likelihood reproduces these values to within a fraction of a percent, supporting the attribution of the improvement to the Fisher-matrix error propagation rather than to the sampler. The search-stage astrophysical prior improves per-source distance estimates but leaves the hierarchical inference essentially unchanged.

astro-ph.GA↗

arXiv2026

Emergent gravitational action from non-local $T\bar T$-like deformations

We study the gravitational effective action induced, at first order in the deformation parameter, by non-local $T\bar T$-like deformations of quantum field theories. Using a heat-kernel formulation, we extract the local geometric terms generated by stress-tensor two-point functions, and apply the construction to free fermions, massive Maxwell theory, and second-order Yang-Mills theory. While the resulting coefficients are generally model dependent, conformal field theories contain a universal sector fixed by the central charge $C_T$. After regularization and renormalization, this sector yields finite, scheme-independent contributions organized into a finite set of curvature invariants. We further analyze trace-trace deformations, for which the relevant contact terms are determined by the Weyl anomaly, and derive the corresponding finite gravitational action for a general class of minimal non-local kernels. These results provide a quantum effective-action realization of induced gravity in which universal conformal data determine calculable contributions to the emergent geometric response.

hep-th↗

arXiv2026

Charged Black Holes with a Lorentz--Violating Kalb--Ramond Background

We investigate exact static, spherically symmetric electrically charged black hole solutions in a gravitational theory with spontaneous Lorentz-symmetry breaking induced by a background Kalb--Ramond field. In contrast to previous analyses that retained only one nonminimal curvature coupling, we include the combined effects of the two independent nonminimal curvature couplings and obtain charged black hole solutions both with and without a cosmological constant. Using the Iyer--Wald covariant phase-space formalism, we derive the corrected thermodynamic quantities and analyze the Joule--Thomson expansion, including the inversion curve and the cooling/heating regions. We further apply the topological approach to black hole thermodynamics to characterize the van der Waals-like phase transition and show how the thermodynamic critical temperature and pressure are encoded in the corresponding topological defect curve. These results clarify the thermodynamic and topological signatures of electrically charged black holes in gravity with a Lorentz-violating Kalb--Ramond background.

gr-qc↗

arXiv2026

Qualitative Shadow Anomaly as a Smoking-gun Signature of Nonmetricity

In general relativity and its metric-formalism extensions, the innermost stable circular orbit and the photon ring of a charged black hole contract as the charge increases. In this paper, we discover a qualitative anomaly that violates this universal behavior, serving as a smoking-gun signature of geometric nonmetricity. By considering a minimal coupling between the bosonic field and the independent affine metric, we demonstrate that nonmetricity induces an effective geometric force that triggers a trajectory expansion of both massless and massive bosons with increasing black hole charge. This qualitative inversion directly imprints onto the black hole shadow, lifting the degeneracy between metric-affine gravity and general relativity. Using Eddington-inspired Born-Infeld gravity as a concrete implementation, we show that next-generation horizon-scale imaging can resolve this signature, probing a complementary high-energy window up to the $10^{5}_{~}\,\text{TeV}$ scale.

gr-qc↗

arXiv2026

Real Part Emergence in Purely Imaginary Quasinormal Modes in Perturbed de Sitter Braneworlds

For braneworlds with infinite extra dimensions, an analysis of the stability of the characteristic spectrum is essential for understanding their dynamical properties. In this study, we investigate the stability of the gravitational perturbation spectrum in a thick de Sitter brane. Unlike the flat brane case, the de Sitter brane features purely imaginary quasinormal frequencies, corresponding to time-domain signals that decay without oscillation. Our results demonstrate that, upon introducing perturbations on the brane, the originally purely imaginary modes develop a nonvanishing real part that depends on the perturbation parameters, thereby becoming complex-frequency modes with both real and imaginary components. In the time domain, this behavior manifests as transient oscillatory signatures in the intermediate stage of the signal, whose fitted frequencies are consistent with those of the first newly induced quasinormal mode, while the late-time waveform remains dominated by the zero mode. As early-time signals are more readily observable, such perturbation-induced oscillations are more likely to be detectable and may have an impact on the extraction of the cosmological constant on the brane from gravitational signals.

gr-qc↗

arXiv2026

Improving the resolution of double white dwarf systems with spaceborne gravitational wave observatories using a robust astrophysical prior

Resolving the crowded population of double white dwarf (DWD) binaries in data from spaceborne gravitational wave (GW) observatories (e.g., LISA, Taiji) remains a major analysis challenge. Comparable performance on addressing this problem has been achieved with two main approaches: global fit, in which resolvable sources are estimated simultaneously from the data, and iterative, where sources are estimated one at a time and subtracted out from the data. While the latter is computationally efficient, methods developed under this approach have traditionally followed a frequentist framework that ignores astrophysical priors. This work incorporates a strong astrophysical prior, derived from the mass limits of detached white dwarfs and linking the GW signal frequency $f$ with its time derivative $\dot{f}$, into the iterative $\mathtt{GBSIEVER}$ pipeline. Applied to simulated LISA and LISA-Taiji network data, the method increases the number of confidently resolved sources by ${\approx}7.3\%$ (LISA-only) and ${\approx}14.6\%$ (network), respectively, and improves parameter estimation accuracy. The improvement persists across multiple realistic DWD population realizations, including in the low-frequency confusion-dominated regime, demonstrating the robustness and practical utility of astrophysically informed priors in iterative source extraction.

gr-qc↗

arXiv2026

Black Hole Entropy Beyond the Wald Term in Nonminimally Coupled Gravity: A Covariant Phase Space Decomposition

We study the entropy of static, spherically symmetric black holes in diffeomorphism-invariant theories with nonminimal matter--curvature couplings, using the covariant phase space formalism. For regular bifurcate Killing horizons, the Iyer--Wald construction gives the standard Wald entropy. If a matter field cannot be smoothly extended to the regular bifurcation surface, however, the entropy-sector horizon surface charge variation can contain finite contributions that are not included in the Wald entropy density. In the representative obtained by directly varying the action, and after ordinary non-gravitational boundary terms have been separated into the work sector, we decompose the entropy entering the first law of black hole thermodynamics as $\SH=\SW+\Sone+\DeltaS$. Here $\SW$ is the Wald entropy, $\Sone$ is the non-Wald part of the entropy-sector Noether charge, and $\DeltaS$ is the remaining integrable part of the entropy-sector horizon surface charge variation. Applying this criterion to Kalb--Ramond, bumblebee, and extended Gauss--Bonnet black holes, we find that the regular Kalb--Ramond branch has $\SH=\SW$, the bumblebee branches yield either $\Sone=0$ with $\DeltaS\neq0$ or a cancellation between $\Sone$ and $\DeltaS$, and the Weyl-vector extended Gauss--Bonnet examples require both corrections. This provides a direct test of whether the Wald density is sufficient or whether the full horizon surface charge variation is required.

gr-qc↗

arXiv2026

Dyonic Black Holes in Lorentz-Violating Gravity with a Background Kalb--Ramond Field

By introducing a nonminimal coupling between the Kalb--Ramond field and the electromagnetic field, we construct an exact four-dimensional static, spherically symmetric dyonic black hole solution in Lorentz-violating gravity with a background Kalb--Ramond field. The curvature invariants show that the spacetime retains a genuine curvature singularity at $r=0$. We then analyze the geodesic motion of null and timelike particles and obtain the photon-sphere radius, the shadow radius, and the innermost stable circular orbit, demonstrating that both the Lorentz-violating parameter and the dyonic charges can appreciably modify the shadow size and the domain of stable circular motion. In the extended phase space, we derive the thermodynamic quantities and verify the first law of black hole thermodynamics together with the Smarr relation. The system also exhibits a first-order phase transition between small and large black holes, and its phase structure is strongly influenced by the Lorentz-violating parameter and the dyonic charges.

gr-qc↗

arXiv2026

Stringy Effects on Holographic Complexity: The Complete Volume in Dynamical Spacetimes

We investigate the stringy effects on holographic complexity in $(d+1)$-dimensional Gauss-Bonnet gravity using the ``complete volume'' proposal for higher-curvature theories. Our analysis covers unperturbed eternal black holes, as well as the one-sided and two-sided Vaidya spacetimes. The one-sided geometry describes a null shell collapsing into the empty AdS vacuum to form a black hole, while the two-sided geometry represents a null shell injected into an eternal black hole background with arbitrary energy. For unperturbed backgrounds, higher-curvature terms introduce explicit corrections to the standard CV proposal, giving rise to a ``competition effect'' absent in the uncorrected framework. In the dynamical settings, we demonstrate that despite novel jumps in the canonical velocities across the null shell, the complexity growth rate remains universally governed by the conserved momentum, just as in Einstein gravity. Furthermore, our two-sided shock wave analysis reveals that Gauss-Bonnet corrections prolong the critical time, preserving the universal logarithmic dependence for the scrambling time.

hep-th↗

arXiv2026

Gravitational-Bumblebee perturbations: Exact decoupling and isospectrality

In this paper, we present the exact decoupling of the full metric and bumblebee field perturbations in a Schwarzschild-like background. The coupled system reduces to four decoupled master equations, revealing in each parity sector a Schwarzschild-like gravitational sector and a Lorentz-violating Maxwell-like vector sector. While Lorentz violation modifies the propagation speed of the emergent vector modes, we demonstrate that the gravitational master modes exhibit a ``dynamical immunity'' to the non-minimal Lorentz-violating coupling, and that the odd- and even-parity perturbations remain strictly isospectral. Our work provides a rare example in which Lorentz-violating couplings reshape the field reconstruction while leaving the gravitational ringdown spectrum intact. This mismatch in propagation speeds suggests a possible timing signature of bumblebee vector dynamics in black hole perturbations, offering a theoretical route to testing spontaneous Lorentz symmetry breaking in the era of multi-messenger astronomy.

gr-qc↗

arXiv2026

Spontaneous Symmetry Breaking and the Emergent Einstein-Standard Model: From Weyl x SU (2)L x U (1)Y Gauge Theory to Geometric Mass Generation

We construct a Weyl x SU(2)_L x U(1)_Y invariant theory by extending four-dimensional Weyl quadratic gravity with Weyl-invariant scalar, fermion, Yukawa and gauge sectors. The quadratic structure (R^tilde - mu^2 |phi|^2)^2 allows the Weyl Goldstone mode to be extracted via a Stueckelberg mechanism independent of the Higgs field. Spontaneous breaking of Weyl gauge symmetry reduces the Weyl quadratic curvature to the Einstein-Hilbert action with a positive cosmological constant, generates a mass term for the Weyl gauge field, and simultaneously produces the Higgs potential -mu^2 |phi|^2 + lambda^2 |phi|^4, which is otherwise forbidden by the symmetry. Our framework unifies the Stueckelberg, Higgs and Yukawa mechanisms, reproduces Standard Model mass generation, and predicts additional Higgs-induced contributions to the Weyl gauge field mass, together with a set of Higgs-Weyl couplings. These interactions provide new phenomenological handles, including a vector dark matter candidate, and highlight the geometric origin of mass.

hep-ph↗

arXiv2026

Topology of black hole thermodynamics: A brief review

Recent explorations of topological aspects in black hole thermodynamics have achieved unprecedented progress. By utilizing topological numbers, different black hole systems can be categorized into distinct universality classes. This universal classification is particularly evident in thermodynamic limits, offering valuable insights for developing a comprehensive quantum gravity framework. This review highlights the latest advancements in this field. Specifically, we outline fundamental topological frameworks underlying black hole solutions, critical points, Davies points, and the Hawking-Page phase transition. For each scenario, we calculate the associated topological numbers and analyze their physical significance. Furthermore, we explore the practical implications arising from this research.

gr-qc↗

arXiv2026

Spectral Butterfly Effect and Resilient Ringdown in Thick Braneworlds

The quasinormal mode spectrum is a unique fingerprint linking gravitational-wave observations to extra-dimensional geometry. In this Letter, we show that thick braneworlds exhibit a spectral butterfly effect: infinitesimal deformations of the effective potential trigger dramatic migrations of quasinormal modes, challenging the presumed stability of this fingerprint. Frequency-domain instabilities depend sensitively on the perturbation's location and strength. In the time domain, near-brane perturbations primarily modify the early ringdown, while far-brane perturbations generate clean late-time echoes. Crucially, the graviton zero mode remains localized, preserving four-dimensional gravity. Despite this pronounced spectral fragility, the observable early-stage signal under current detector sensitivities is still dominated by the original fundamental mode. Hence, thick braneworlds display a nontrivial coexistence of a fragile spectrum and a resilient ringdown, supporting the continued use of the standard fingerprint in present-day gravitational-wave astronomy while revealing its hidden sensitivity.

gr-qc↗

arXiv2026

Macroscopic Optical Nonreciprocity: A Black Hole as an Optical Diode

Optical reciprocity--the principle that light retraces the same path when source and detector are interchanged--is a foundational concept in geometric optics. In this Letter, we demonstrate that this ``symmetry-protected'' behavior can be qualitatively overturned in a rotating black hole when spontaneous Lorentz symmetry breaking introduces a nonminimally coupled background structure with a preferred direction. Through numerical ray-tracing simulations, we reveal a striking macroscopic signature: upon optical-path reversal achieved by exchanging the source and the observer, the shadow of the same black hole morphs from a quasi-symmetric rugby-ball shape into a distinct teardrop profile. This high-contrast nonreciprocity effectively turns the black hole into a cosmic-scale optical diode, offering a novel pathway to probe fundamental symmetries using current and next-generation horizon-scale imaging.

gr-qc↗

arXiv2026

Correlators in $T\bar{T}$ and Root-$T\bar{T}$ Deformed CFTs

Quasi-primary correlators in two-dimensional conformal field theories deformed simultaneously by $T\bar T$ and root-$T\bar T$ are studied. A path-integral formulation motivated by the geometric realization of the combined deformation is used to develop a geometric framework for evaluating the deformed correlators. Within this framework, the two-point function is obtained to all orders in the $T\bar T$ coupling and to leading order in the root-$T\bar T$ coupling, while the leading correction to the three-point function is computed. It is further shown that the deformed two-point correlator admits a kernel representation as a weighted average of undeformed CFT correlators over conformal dimensions. This representation is derived explicitly for both the pure $T\bar T$ deformation and the combined flow. In this way, the mixed $T\bar T$/root-$T\bar T$ deformation is incorporated into the geometric description of irrelevant deformations, and the structure of local correlators beyond the pure $T\bar T$ case is characterized more explicitly.

hep-th↗

arXiv2026

Topologically equivalent yet radiatively distinct orbits in EMRI system

Multiple potential wells for massive test particles, allowing distinct families of bound orbits to coexist, are a characteristic feature of certain exotic compact objects beyond general relativity. Taking the dyonic black hole as a representative example, we demonstrate that such multi-well geometries generically support multiple coexisting branches of bound orbits, in contrast to the single-branch behavior observed in the Schwarzschild spacetime. Crucially, the periodic orbits sharing identical rational rotation number, and hence identical topological indices can nevertheless produce \emph{radiatively distinct} gravitational waves in a representative extreme-mass-ratio inspirals: their amplitude modulation and harmonic content differ because each branch spans different regions of spacetime curvature. These ``topologically equivalent yet waveform-distinguishable'' signatures provide a direct observational probe of strong field gravitational dynamics beyond general relativity, potentially accessible to future space-based gravitational wave detectors.

gr-qc↗

arXiv2026

Self-resonance preheating in deformed attractor models: oscillon formation and evolution

It is well known that, in potentials that are quadratic near the minimum but shallower away, such as small $α$ ($\ll M_P^2$) attractors, the inflaton condensate fragments into localized compact objects known as oscillons during self-resonance preheating. In this work we investigate the self-resonance in deformed $α$-attractor T-model with a Gaussian feature near the minimum, distant from inflation's end. Linear analysis reveals altered resonance bands and deformed Floquet charts dependent on feature parameters. In fully nonlinear lattice simulations, we find that the gradient energy transfer is largely independent of the potential feature parameter $h$. In contrast, after resonance terminates, the subsequent evolution of gradient energy becomes strongly dependent on $h$. Statistical analysis reveals that models with the potential feature produce larger number of smaller oscillons, with a reduced energy stored in these objects, increasingly suppressed as the magnitude of $h$ grows. By tracking the total energy and the gradient energy contained in oscillons, we find that in models with nonzero $h$ oscillons are systematically shorter-lived, with this effect strengthening for larger $h$. The gravitational wave emission is dominated by the resonance stage and is strongly suppressed once oscillons form. Potential features leave the low-frequency spectrum largely unchanged but significantly modify the high-frequency tail. Although a complete reheating description requires external couplings and higher-resolution simulations, clear qualitative differences of cosmic expansion history already emerge within our simulated time window. These results highlight the important role of potential features in shaping reheating dynamics and their cosmological implications, and provide a deeper understanding of preheating dynamics and the properties of oscillons.

astro-ph.CO↗

arXiv2026

Gravity/thermodynamics correspondence via black hole shadows

The shadow of a black hole serves as a pristine window into the strong-gravity regime, with cuspy feature emerging as a smoking-gun signature of physics beyond the Kerr paradigm. In this paper, we extend the work of [arXiv:2601.15612 [gr-qc]] and study the detailed properties of the cuspy shadow by using the parametric expressions of the shadow boundary. From a topological perspective, we provide a rigorous topological classification of these shadows, categorizing them into distinct ``rectangular" and ``8-shape" topologies. Crucially, we establish a formal gravity/thermodynamics correspondence by mapping the cuspy shadow to the swallowtail behavior observed in thermodynamic free energy. We demonstrate that the self-intersection of the shadow boundary, marking a geometric phase transition, can be precisely determined through three independent but equivalently thermodynamic-like approaches. Furthermore, we analytically derive the critical exponents governing the emergence of these cusps, revealing that they are consistent with the mean-field universality class. Our results suggest that the observational features of black hole shadows are deeply rooted in the underlying gravitational thermodynamics, offering a novel framework to probe the fundamental nature of spacetime.

gr-qc↗