Scalar-induced neutrinoless double beta decay in SU(5)

A bstract We discuss the role of heavy scalar fields in mediating neutrinoless double beta decay (0 νββ ) within the SU(5) Grand Unified Theory framework, extended suitably to include neutrino mass. In such a minimal realistic SU(5) setup for fermion masses, the scalar contributions to 0 νββ are extremely suppressed as a consequence of the proton decay bound. We circumvent this problem by imposing a discrete $${\mathcal{Z}}_{3}$$ symmetry. However, the scalar contributions to 0 νββ remain suppressed in this $$\text{SU}(5)\times {\mathcal{Z}}_{3}$$ model due to the neutrino mass constraint. We find that the 0 νββ contribution can be enhanced by extending the scalar sector with an additional 15 -dimensional scalar representation with suitable $${\mathcal{Z}}_{3}$$ charge. Such an extension not only yields realistic fermion mass spectra but also leads to experimentally testable predictions in upcoming ton-scale 0 νββ searches, which can be used as a sensitive probe of the new scalars across a broad range, from LHC-accessible scales up to ∼ 10 10 GeV.