A flavour GUT model with θ13PMNS≃θC/2

We propose a supersymmetric SU(5) GUT model with an A4 family symmetry - including a full flavon and messenger sector - which realises the relation θ13PMNS≃θC/2. The neutrino sector features tri-bimaximal mixing, and θ13PMNS≃θC/2 emerges from the charged lepton contribution to the PMNS matrix, which in turn is linked to quark mixing via specific GUT relations. These GUT relations arise after GUT symmetry breaking from a novel combination of group theoretical Clebsch-Gordan factors, which in addition to large θ13PMNS lead to promising quark-lepton mass ratios for all generations of quarks and leptons and to ms/md=18.95−0.24+0.33, in excellent agreement with experimental results. The model also features spontaneous CP violation, with all quark and lepton CP phases determined from family symmetry breaking. We perform a full Markov Chain Monte Carlo fit to the available quark and lepton data, and discuss how the model can be tested by present and future experiments.