Convergence of the diffuse-scatter redshift exponent calibration

Determine whether values of the turboFRB diffuse-channel redshift exponent \(\gamma_s\) below \(-1.460\) improve the calibration objective and identify a converged minimum for this nuisance parameter.

Background

The turboFRB forward model calibrates four effective parameters against the corrected IllustrisTNG ray-tracing benchmark, including γs\gamma_s, the redshift exponent governing the log-scatter of the diffuse intergalactic-medium channel. The reported optimum lies at the lower boundary explored during the refinement for this parameter. Because lower values were not scanned, the paper does not establish that the reported value is a genuine minimum rather than a boundary value, leaving the calibration of the diffuse-channel redshift evolution unresolved.

References

For $\gamma_s$ the refinement returns the lowest value it explores ($\gamma_s=-1.46$, against $-1.38$ one step above), and smaller values were not scanned; we therefore do not claim a converged minimum in $\gamma_s$.

— A stochastic forward model for the intergalactic dispersion-measure distribution of Fast Radio Bursts  (2608.17658 - Fortunato et al., 18 Aug 2026) in Section 2, subsection “Parameter classification and calibration”