Probing Circular Polarization and Doppler-Induced Dipole Anisotropies in the Stochastic Gravitational-Wave Background

Sevgi Karadag^1*, Chia-Hsuan Hsiung², Guo-Chin Liu², Kin-Wang Ng¹, Henry Tsz-King Wong¹

¹Institute of Physics, Academia Sinica, Taipei, Taiwan
²Department of Physics, Tamkang University, New Taipei, Taiwan

* Presenter:Sevgi Karadag, email:sevgik@as.edu.tw

Some inflationary and parity-violating models predict the existence of a circularly polarized stochastic gravitational-wave background (SGWB), whose detection would have far-reaching cosmological implications. This work presents a comprehensive simulation and analysis framework designed to characterize circular polarization and Doppler-induced dipole anisotropies in the SGWB. The analysis incorporates both the monopole (isotropic) and dipole (kinematic) components, the latter arising from our motion relative to the cosmic rest frame.

We implement a parameter-estimation pipeline that jointly constrains the polarization degree (Π), monopole and dipole amplitudes (Ω_GW and D_\alpha). The framework is first validated using simulated circularly polarized signals, confirming its reliability in recovering key parameters under anisotropic conditions. Applying the pipeline to Advanced LIGO’s first three observing runs (O1–O3), we derive upper limits on Π, Ω_GW, and D_\alpha, and demonstrate the method’s capability to distinguish anisotropic features. Finally, we project the sensitivity of next-generation detectors, including the Einstein Telescope (ET) and Cosmic Explorer (CE), showing their enhanced potential to detect or constrain circular polarization and kinematic dipoles in the SGWB. Our findings establish a robust methodology for exploring polarization and anisotropy in the stochastic gravitational-wave background, paving the way for uncovering parity-violating signatures in future gravitational-wave observations.

Keywords: Gravitational Waves, SGWB, dipole anisotropies, circular polarization