arXiv subjects

Yun-Tao Gu

Publications and source records attributed to Yun-Tao Gu.

4 recordsLinked to original sources

arXiv2026

Pseudospectrum of Braneworld Perturbations

Pseudospectral analysis provides a powerful way to probe the spectral stability of non-self-adjoint operators and has been widely used in black hole physics, but its application to braneworld scenarios has not yet been explored. In this work, we apply this method to tensor gravitational perturbations in a representative scalar-field-generated thick brane background. To the best of our knowledge, we provide the first hyperboloidal formulation of braneworld perturbations and propose a height-function gauge adapted to the warped geometry. This construction converts the outgoing boundary conditions of quasinormal modes into regularity conditions at finite compactified boundaries and recasts the perturbation equation as a first-order system generated by a non-self-adjoint hyperboloidal evolution operator. With the corresponding energy norm, we compute the condition numbers and pseudospectra of the localized graviton zero mode and the quasinormal-mode spectrum. We find that the condition numbers grow rapidly along the overtone sequence and that the corresponding pseudospectral contours develop broad, connected structures in the high-overtone region. These results show a strongly mode-dependent spectral sensitivity: among the damped modes analyzed, the higher overtones are less robust than the fundamental mode. The zero mode also has a larger condition number than the fundamental mode, indicating stronger local first-order sensitivity. These diagnostics characterize sensitivity to generic norm-bounded operator perturbations. Relating that sensitivity to a specific braneworld deformation requires the corresponding self-consistent perturbation constraints.

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

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↗

arXiv2025

Quasinormal modes of an electrically charged Kalb-Ramond black hole

Lorentz violation serves as a significant feature in many modified theories of gravity. In particular, spontaneous Lorentz violation induced by the Kalb-Ramond field has attracted considerable attention. Recently, an electrically charged black hole solution within the Kalb-Ramond framework was proposed. In this study, we investigate the quasinormal modes of the resulting ``undecouplable'' system using both the matrix-valued continued fraction method and the matrix-valued direct integration method. Additionally, we develop a new approach to distinguish between different modes in such ``undecouplable'' systems. An error analysis is performed, and the influence of Lorentz violation on the fundamental quasinormal modes is systematically analyzed within a suitable parameter range.

gr-qc↗