Population-level identifiability of component-spin distributions

Determine whether information beyond the effective-spin parameters combines at the binary-black-hole population level to constrain the component spin distribution, rather than merely reflecting extrapolation from the effective-spin distribution and model priors.

Background

The paper emphasizes that gravitational-wave observations typically constrain the aligned and precessing effective spins more strongly than the four underlying component-spin quantities: the two spin magnitudes and the two spin tilts. Effective spins are lossy combinations of these component properties, so multiple component-spin populations can produce similar effective-spin distributions.

The authors note that some individual events contain information beyond effective spins, but explicitly leave unresolved whether such information accumulates across the population sufficiently to constrain the component-spin distribution. This question is central to determining whether inferred preferences for spin orientations have a direct astrophysical basis or are induced by population-model assumptions.

References

There is information beyond the effective spins contained in some individual events . However, it is not yet clear if this information combines at the population level to provide constraints on the component spin distribution .

— Binary-black hole spin population results may be driven by prior degeneracies  (2609.10753 - Wolfe et al., 9 Sep 2026) in Section preceding “Hierarchical Inference” (Introduction)