| Summary: | Abstract Within a chiral SU(15) gauge theory in which the Standard Model fermions are bound states of massless preons, we show that proton-decay operators are likely induced at the compositeness scale, Λpre. Our estimate of the limit imposed by searches for proton decays is Λpre > 104 TeV1/2 C 8 1 / 4 m Q 1 / 2 $$ {C}_8^{1/4}\ {m}_{\mathcal{Q}}^{1/2} $$ , where C 8 is a rescaled coefficient of an 8-prebaryon operator induced by SU(15) dynamics, and m Q $$ {m}_{\mathcal{Q}} $$ is the mass of a composite vectorlike quark. The latter has a lower limit related to the mass of a composite vectorlike lepton, which in turn is required by LHC searches to be above 1 TeV. For C 8 in the 10 −5 – 1 range, the lower limit on Λpre varies between 3 × 103 TeV and 5 × 104 TeV. We point out that exotic proton decay modes, into a π + and a heavy right-handed neutrino, could be observed using the Super-Kamiokande or DUNE detectors.
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