Sterile neutrino contribution to neutrinoless double beta decay in χEFT framework

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 ( 0ν β β 0 ν β β ) decay process. 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 spans over a wide range of masses ~ ∼ (keV-TeV) of sterile neutrinos, we adopt the chiral effective field theory approach to calculate the half-life and effective mass in the 0ν β β 0 ν β β 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.