Beta and Neutrinoless Double Beta Decays with KeV Sterile Fermions

Motivated by the capability of the KATRIN experiment to explore the existence of KeV neutrinos in the $[1-18.5]$ KeV mass range, we explore the viability of minimal extensions of the Standard Model involving sterile neutrinos (namely the 3 + $N$ frameworks) and study their possible impact in both the beta energy spectrum and the neutrinoless double beta decay effective mass, for the two possible ordering cases for the light neutrino spectrum. We also explore how both observables can discriminate between motivated low-scale seesaw realizations involving KeV sterile neutrinos. Our study concerns the prospect of a Type-I seesaw with two right-handed neutrinos, and a combination of the inverse and the linear seesaws where the Standard Model is minimally extended by two quasi-degenerate sterile fermions. We also discuss the possibility of exploring the latter case searching for double-kinks in KATRIN.