The Seesaw Mechanism and the Structure of Spacetime above the Electroweak Scale

Abstract

According to the seesaw mechanism, neutrino masses arise from the existence of heavy Majorana neutrinos postulated to emerge near the grand unification scale (GUT) of about 10¹⁶ GeV. Despite its theoretical appeal, this scenario involves either physics at inaccessible scales or tuning the Yukawa couplings to un-naturally low values. Our work sidesteps the seesaw mechanism and shows that neutrino masses follow from placing the Standard Model on a spacetime support equipped with arbitrarily small deviations from four dimensions.