Probing the Orientation Distribution of Nearby Double White Dwarfs through Gravitational Waves with LISA
arXiv:2607.13363
The paper introduces a method to infer the orientation distribution of nearby double white dwarf binaries from LISA gravitational‑wave observations, using a spherical‑harmonic (Wigner‑D) framework that accounts for polarization angle degeneracies.
Abstract
We present a framework to study the orientation distribution of nearby double white dwarf binaries with LISA, explicitly accounting for the fourfold degeneracy in the polarization angle. Exploiting the belt-like sky distribution of the nearby sample along the Galactic plane, we show that the low-multipole extraction can be recast as an effectively one-dimensional Fourier analysis along Galactic longitude, within a spherical-harmonic expansion based on the Wigner-\(D\) formalism. The symmetry with respect to the Galactic plane governs the sensitivity: modes even under reflection across the plane remain accessible, while odd modes are strongly suppressed. For a fiducial sample of about 500 binaries within \(\lesssim 4\) kpc, corresponding to roughly 5\% of the resolved Galactic population, the method yields an uncertainty of order 0.02 for the even coefficients with \(\ell \leq 3\), and is readily applicable to the forthcoming LISA catalog.
9 pages, 2 figures