Dark matter motivated sterile neutrino contribution to neutrinoless double beta decay
The exact seesaw relation in a type-I seesaw framework puts constraints on the relations between active and sterile neutrino sectors in terms of their masses and mixing angles. In such a setup, we employ a model-independent approach to investigate the signature of sterile neutrinos in the half-life of the neutrinoless double beta ($0νββ$) decay process. In particular, we aim to study the contribution of sterile neutrinos in the mass range $\sim$~keV that is motivated by the dark matter constituent of the Universe. Further, the masses of the sterile neutrinos are determined by the active neutrino masses, mixing angles, and phases, and active-sterile mixing angles and $CP$-violating phases. The parameter space is constrained by the exact seesaw relation, thereby making the analysis constrained. After capturing the parameter space that can account for $\sim~$keV scale masses for the sterile neutrinos, we adopt the chiral effective field theory approach to calculate the half-life and effective mass in the $0νββ$ decay. As the study transitions from the TeV scale to scenarios involving at least one sterile neutrino in the keV mass range, it reveals a significant modification of the effective mass. In particular, the cancellation region associated with the normal mass hierarchy for TeV-scale sterile neutrinos no longer persists when a keV-scale sterile neutrino is introduced, resulting in a finite effective mass that future experiments can probe. Likewise, the involvement of keV-scale sterile neutrino in the inverted mass hierarchy case makes the band distorted and scattered points appear around the main band.