Elwin K. Y. Li | Search arXiv

arXiv2026

Turning Selection Bias into a New Statistic: Asymmetry and Fringes of Lensed Gravitational Waves

Gravitational waves (GWs) propagating across the Universe can be distorted by intervening lenses, producing characteristic wave-optics signatures. These effects are not incorporated into current matched-filtering searches and can therefore substantially reduce detection efficiency. The underlying mechanism is the signal-consistency test, which measures deviations between the observed and expected signal-to-noise ratio (SNR) distributions. We report a systematic study of the impact of gravitational lensing on signal-consistency tests, using a two-image interference model and representative signal-consistency statistics in both the time and frequency domains. We find that overlapping images produce sharply localized SNR residuals in the time domain, breaking the reflection symmetry of the autocorrelation about the merger time. Although interference fringes produce broadband SNR residuals in the frequency domain, both domains exhibit a minimum for high-mass signals when the fringe structure becomes comparable to the signal bandwidth. This highlights a limitation of current strategies that search for distorted lensed signals only among GW events detected by matched-filtering searches. Exploiting this asymmetry, we develop a statistic that separates selected down-ranked lensed injections from noise-background triggers and paired nonlensed injections, without extending the template bank. Our results establish the first connection between lensing observables and detection, paving the way for the discovery of lensed GWs.

gr-qc↗

arXiv2026

Investigating the effect of sensitivity of KAGRA on sky localization of gravitational-wave sources from compact binary coalescences

The addition of KAGRA to the global gravitational-wave detector network introduces new baselines and complementary antenna response patterns that can enhance sky localization for compact binary coalescences. We investigate KAGRA's role in the LIGO-Virgo-KAGRA network using a systematic injection study of binary neutron star signals. Sky maps are constructed with a radiometric, coherence-based framework, allowing isolation of geometric and timing contributions from individual detectors. Localization performance is quantified using the fraction of events localized within $100~\mathrm{deg}^2$, cumulative area distributions, and the median $90%$ credible region. We also assess KAGRA's impact on detection rates by varying its sensitivity over a wide range. Even at its current sensitivity of $\sim10~\mathrm{Mpc}$, KAGRA provides measurable improvements by breaking degeneracies through additional baselines and directional constraints. As sensitivity increases, improvements in signal-to-noise ratio and timing precision lead to substantial reductions in localization area. We identify a binary neutron star range of $\sim30~\mathrm{Mpc}$ as a practical benchmark for reliable localization suitable for electromagnetic follow-up, noting this as a conservative estimate. In addition, KAGRA increases the number of detectable events by enabling lower signal-to-noise detections. These results demonstrate that even a modest-sensitivity detector can significantly enhance network performance through geometric complementarity, highlighting the importance of a geographically distributed network for multimessenger gravitational-wave astronomy.

gr-qc↗