A forest of gravitational waves in our Galactic Centre

• Pau Amaro Seoane (Universitat Politècnica de València)

The Galactic Centre contains populations of stellar-mass and substellar-mass compact objects orbiting the central black hole, classified as early extreme-mass ratio inspirals (E-EMRIs) and extremely large mass ratio inspirals (XMRIs). These systems constitute asymmetric binaries, characterized by mass ratios exceeding 10,0000 to 1. This mass differential causes the secondary body to approximate a test particle, completing tens of thousands or millions of orbital cycles prior to coalescence. This high cycle count delineates the spacetime geometry and multipolar structure of the central black hole with greater resolution than comparable-mass supermassive black hole binaries, which undergo rapid coalescence and exhibit fewer in-band cycles. The prolonged orbital data can in principle also facilitate topological analysis. By applying the Gauss-Bonnet theorem, the accumulated orbital precession parameters relate the integrated curvature of the spacetime to its topological invariants. The continuous gravitational wave emission from these populations generates a non-Gaussian, non-stationary composite signal within the frequency band of the Laser Interferometer Space Antenna. This aggregated signal comprises an incoherent superposition of individual waveforms from eccentric and circular orbits, which superimposes upon the spectral signatures of other target sources, including binaries of supermassive black holes and verification binaries. Spectral analysis indicates that sources with minimal frequency drift constitute an unresolved stochastic background, while systems with measurable frequency evolution produce distinct spectral components. Extracting targeted signals from this composite data requires time-frequency domain modeling and non-Poissonian statistical subtraction protocols.

Probing New Physics through Gravitational Wave Detection and Dark Matter Direct Detection

• Mai Qiao (ICTP - AP / University Chinese Academy of Sciences)

Numerous astrophysical observations indicate the existence of dark matter via gravitational effects, yet its nature remains elusive. Experiments exploring non-gravitational interactions between dark matter and Standard Model (SM) particles include indirect, direct, and collider detection. Meanwhile, gravitational-wave (GW) observations of compact binary coalescences since GW150914 also offer valuable opportunities to both probe the early Universe and DM interactions. This talk covers three diverse topics: ultralight DM (ULDM) searches with LIGO data, correlated noise in stochastic gravitational-wave background (SGWB) studies, and MeV-scale light DM detection strategies. Specifically, we discuss ULDM detection using new LIGO data via the cross-correlation, Band-Sampled Data excess power (BSD), and Logarithmic Power Spectral Density (LPSD) methods. Regarding correlated noise, we address strategies to estimate its impact on SGWB research by monitoring magnetic field couplings with GW strain channels. Finally, for light DM, we present constraints on effective operators via cosmic-ray boosted DM (CRDM) with LZ data and analyze potential diurnal modulation effects in underground ionization signals caused by the Earth attenuation.