image from GUTs Original Research Article

The recent observations of the leptonic mixing angle image are consistent with image (with image being the Cabibbo angle image). We discuss how this relation can emerge in Grand Unified Theories (GUTs) via charged lepton corrections. The key ingredient is that in GUTs the down-type quark Yukawa matrix and the charged lepton Yukawa matrix are generated from the same set of GUT operators, which implies that the resulting entries are linked and differ only by group-theoretical Clebsch factors. This allows a link image to be established, which can induce image provided that the 1–3 mixing in the neutrino mass matrix is much smaller than image. We find simple conditions under which image can arise via this link in SU(5) GUTs and Pati–Salam models. We also discuss possible corrections to the exact relation. Using lepton mixing sum rules different neutrino mixing patterns can be distinguished by their predictions for the Dirac CP phase image.