Determining the leading-order contact term induced by sterile neutrinos in neutrinoless double β decay

Sterile neutrinos are present in multiple extensions to the Standard Model and participate in neutrino mass mechanisms, from simple type-I seesaw models to UV complete theories like left-right symmetry. In total analogy to the case of light neutrinos, the neutrinoless double β decay amplitude induced by the exchange of sterile neutrinos requires the introduction of a leading-order, short-range operator. Knowing this contribution is essential to correctly interpret positive experimental results in light of disentangling the underlying physical mechanism. In the absence of any data from experiments or lattice QCD, we present a method to determine the low-energy constant associated with this contract term.