Probing leptogenesis at LISA: a Fisher analysis

In https://doi.org/10.1088/1475-7516/2024/11/051 JCAP11(2024)051, we discussed how different regimes (flavoured) of leptogenesis can be probed through a “tomographic” approach using primordial gravitational waves. By examining the theory's parameter space, we identified regions where right-handed neutrino mass-dependent non-standard cosmological expansion leaves characteristic imprints on propagating gravitational waves. Our analysis focused on inflationary blue-tilted gravitational waves, modeled by a power-law tensor power spectrum with a constant spectral index. The resulting double-peak spectrum — where peak and dip frequencies are sensitive to leptogenesis parameters — provided marked signatures of different leptogenesis regimes. In this follow-up article, we conduct a statistical analysis of two-flavour leptogenesis signals, particularly those producing a peak (more generally, a broken power-law signal) within the LISA frequency band. Using a Fisher matrix analysis, we delineate the regions of parameter space that LISA can probe with minimal uncertainty, accounting for galactic and extragalactic foregrounds along with LISA's instrumental noise.