LIGO Document P2500778-v3
- Mini-Extreme-Mass-Ratio Inspirals (mini-EMRIs), comprising a sub-solar exotic compact object (such as a primordial black hole or boson star) orbiting a much heavier stellar-origin or exotic compact object, represent key targets for ground-based gravitational-wave detectors to probe the early universe and the nature of dark matter.
However, detecting such systems, which could spend hours to years in LIGO, Virgo and KAGRA data, poses a computational challenge to standard matched-filtering methods, which has motivated the development of methods that divide the data into coherent chunks, Fourier transform them, and combine them incoherently. However, these pipelines typically require that the signal be quasi-monochromatic within each chunk, which imposes a fundamental limit on the coherence time, since spectral leakage becomes significant when the frequency evolution within the chunk becomes comparable to the frequency resolution. In this work, we extend the development of our method,ΣTrack, to the regime in which the quasi-monochromatic approximation is relaxed,
in two ways. First, we establish an analytical model for the spectral leakage, extending the validity of conventional analyses beyond the quasi-monochromatic regime. Second, we propose the \( \Sigma R \) statistic---a novel detection metric formed by a weighted summation of power ratios---which effectively recovers the signal energy dispersed across adjacent frequency bins. Building on this framework, we further introduce an innovative frequency-layered search strategy that dynamically optimizes the coherence time across the observation band.
We benchmark our method against a globally optimized Hough transform pipeline using a fiducial mini-EMRI signal from a binary with masses \( (1.5,10^{-5})\,M_\odot \). The results demonstrate that our framework achieves an order-of-magnitude enhancement in the effective detection volume, significantly expanding the horizon for discovering mini-EMRIs and sub-solar exotic compact objects with ground-based gravitational wave detectors, which can be similarly applied to EMRI searches for future space-based gravitational wave detectors.
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