Kata Karácsonyi\(^{1,2}\), Zoltán Keresztes\(^1\) (2026.10.01 - 12.31)

1. University of Szeged
2. HUN-REN Wigner Research Centre for Physics

Publication: Spin-Inversion Degeneracies in Restricted Inspiral Waveforms for LISA

Abstract: We propose a numerical study of how the observability of black-hole spin inversions in massive black-hole binaries depends on the orientation of the source relative to the observer. Using a restricted frequency-domain waveform model developed for the Laser Interferometer Space Antenna (LISA), we will compare waveforms containing spin inversions with the best-fitting waveforms constrained to exhibit no inversion. For three representative binary configurations, the analysis will be repeated at several source inclinations, including face-on, moderately inclined, and edge-on orientations.

Each comparison requires global optimization over the binary mass ratio, spin magnitudes and orientations, total mass, and phase and time offsets. To distinguish genuine physical degeneracies from incomplete numerical convergence, the optimization will be performed independently in all relevant spin-orientation sectors and with multiple random seeds. The best candidates will subsequently be recomputed at progressively higher frequency resolutions, and the stability of the recovered matches and residual signal-to-noise ratios will be verified.

The calculations consist of many independent, CPU-intensive optimization jobs. The resulting orientation-dependent matches and residuals will quantify when spin-inversion signatures remain distinguishable in LISA observations and when they can be mimicked by binaries without spin inversions.