Discrepancy between published JWST sensitivity projections

Determine the origin of the factor-of-two discrepancy between the published JWST NIRSpec sensitivity projections of Janish et al. and Roy et al., which remains unresolved despite the availability of real JWST data.

Background

The paper compares its measured NIRSpec sensitivity with earlier forecasts for detecting decaying axion dark matter using JWST. The projections of Roy et al. and Janish et al. differ by approximately a factor of two, even though both concern the same general instrumental search strategy.

The authors note that this discrepancy is less consequential now that actual JWST data are available, but they do not resolve its origin. It therefore remains an explicitly identified unresolved issue concerning the consistency of prior JWST forecasts.

References

By contrast, the projections of Ref. anticipated somewhat greater sensitivity; the factor of two difference between the published NIRSpec projections of Ref. and Ref. has remained unresolved, and is of lesser present-day importance given the availability of real JWST data.

— Re-examining the sensitivity of JWST to decaying axion dark matter  (2609.10674 - Gemmell et al., 9 Sep 2026) in Section 5.4, “Comparison with other projections and limits” (paragraph beginning “Accounting for the difference…”).