A bstract We explore a class of realistic supersymmetric hybrid inflation models with a predicted scalar spectral index n s ≈ 0 . 97 − 0 . 978, which is in good agreement with the recent Atacama Cosmology Telescope (ACT) measurement. The waterfall field responsible for the gauge symmetry breaking in this scenario experiences some e -foldings during the inflationary epoch. The scalar perturbations associated with the waterfall field during this phase induce a stochastic gravitational wave spectrum that will be tested in the ongoing Pulsar Timing Array (PTA) measurements and in future experiments. In an SU(5) setting an observable number density of the superheavy GUT monopole linked to the waterfall field can be realized.
Moursy et al. (2026) studied this question.