arXiv subjects

Hayato Imafuku

Publications and source records attributed to Hayato Imafuku.

3 recordsLinked to original sources

arXiv2026

Detectability of avoided crossings in black hole ringdowns

Quasinormal modes (QNMs) of black holes can exhibit avoided crossings (ACs), in which specific QNM frequencies approach each other while their amplitudes are enhanced and acquire nearly opposite phases, leading to characteristic interference. Resolving such closely spaced modes through black hole spectroscopy is observationally challenging. In this paper, we investigate the detectability of nearly degenerate QNMs in the presence of an AC within a Bayesian framework using three waveform models. We examine how the inference of the complex frequencies and amplitudes depends on the separation between the two QNM frequencies and on the choice of template waveform. We find that resolving the individual QNM frequencies is difficult even under optimistic conditions. On the other hand, collective waveform signatures associated with ACs may still be identified through complementary waveform descriptions, provided that the AC-related modes dominate the observed ringdown signal and contamination from more slowly damped modes is negligible or can be removed.

gr-qc↗

arXiv2025

Observational constraints on the nonlinear regime of gravity with a parametrized beyond-GR gravitational waveform model

Gravitational waves from compact binary coalescences provide unique opportunities to test general relativity (GR) in the strong-field regime. In particular, the merger phase, during which two compact objects finally coalesce, corresponds to the regime of the strongest gravitational fields accessible by direct observation and thus serves as a probe of the nonlinear nature of gravity. In this work, we test GR in the merger phase by analyzing GW150914 using a modified waveform proposed in [Watarai et al. 2024], which parametrizes possible deviations from GR during this stage. Within this framework, the inferred deviation parameters can be translated into model-independent constraints on physically meaningful quantities. For GW150914, we find that the additional energy radiated in the merger phase is constrained to be $0.26^{+0.75}_{-0.62}~\%$ of the total energy emitted over the entire coalescence predicted by GR, and the deviation in the coalescence time is $2.17^{+9.56}_{-9.90}~\mathrm{ms}$, both within the $90\%$ credible interval. These two constraints serve as observational benchmarks for deviations in the nonlinear gravity regime, offering guidance for theoretical investigations of beyond-GR models.

gr-qc↗

arXiv2025

Statistical biases in parametrized searches for gravitational-wave polarizations

In tests of gravity using gravitational waves (GWs), GW events analyzed are often selected based on specific criteria, particularly the signal-to-noise ratio. However, such event selection can introduce bias into parameter estimation unless the selection effect is appropriately taken into account in the analysis. In this paper, we investigate how event selection with certain prior information affects parameter inference within the scalar-tensor polarization framework, focusing on the measurement of the scalar mode amplitude parameters. We find that for the Tensor+Scalar(dipole) model, the amplitude of the scalar dipole radiation is overestimated when its true value is nonzero while there is no false deviation in the absence of the scalar mode. The same bias is expected to occur also for the Tensor+Scalar(quadrupole) model. However, the error typically exceeds the bias as the scalar quadrupole mode is difficult to be distinguished from the tensor mode.

gr-qc↗