Group theoretical factors from GUT symmetry breaking can lead to predictions for the ratios of quark and lepton masses (or Yukawa couplings) at the unification scale. Due to supersymmetric (SUSY) threshold corrections the viability of such predictions can depend strongly on the SUSY parameters. For three common minimal SUSY breaking scenarios with anomaly, gauge and gravity mediation we investigate which GUT scale ratios m e /m d , m µ /m s , y τ /y b and y t /y b are allowed when phenomenological constraints from electroweak precision observables, B physics, (g − 2) µ , mass limits on sparticles from direct searches as well as, optionally, dark matter constraints are taken into account. We derive possible new predictions for the GUT scale mass ratios and compare them with the phenomenologically allowed ranges. We find that new GUT scale predictions such as m µ /m s = 9/2 or 6 and y τ /y b = 3/2 or 2 are often favoured compared to the ubiquitous relations m µ /m s = 3 or y τ /y b = 1. They are viable for characteristic SUSY scenarios, testable at the CERN LHC and future colliders.
We propose new classes of models which predict both tri-bimaximal lepton mixing and a right-angled Cabibbo-Kobayashi-Maskawa (CKM) unitarity triangle, α ≈ 90 • . The ingredients of the models include a supersymmetric (SUSY) unified gauge group such as SU(5), a discrete family symmetry such as A 4 or S 4 , a shaping symmetry including products of Z 2 and Z 4 groups as well as spontaneous CP violation. We show how the vacuum alignment in such models allows a simple explanation of α ≈ 90 • by a combination of purely real or purely imaginary vacuum expectation values (vevs) of the flavons responsible for family symmetry breaking. This leads to quark mass matrices with 1-3 texture zeros that satisfy the "phase sum rule" and lepton mass matrices that satisfy the "lepton mixing sum rule" together with a new prediction that the leptonic CP violating oscillation phase is close to either 0 • , 90 • , 180 • , or 270 • depending on the model, with neutrino masses being purely real (no complex Majorana phases). This leads to the possibility of having right-angled unitarity triangles in both the quark and lepton sectors.
We investigate the effect of supersymmetric (SUSY) threshold corrections on the values of the running quark and charged lepton masses at the GUT scale within the large tan β regime of the MSSM. In addition to the typically dominant SUSY QCD contributions for the quarks, we also include the electroweak contributions for quarks and leptons and show that they can have significant effects. We provide the GUT scale ranges of quark and charged lepton Yukawa couplings as well as of the ratios m µ /m s , m e /m d , y τ /y b and y t /y b for three example ranges of SUSY parameters. We discuss how the enlarged ranges due to threshold effects might open up new possibilities for constructing GUT models of fermion masses and mixings.
The recent results from T2K and MINOS experiments point towards a relatively large value of the reactor angle θ 13 in the lepton sector. In this paper we show how a large θ 13 can arise from the charged lepton sector alone in the context of an SU(5) GUT. In such a scenario (tri-)bimaximal mixing in the neutrino sector is still a viable possibility. We also analyse the general implications of the considered scenario for the searches of CP violation in neutrino oscillations.
We present a SUSY SUð5Þ Â T 0 unified flavor model with type I seesaw mechanism of neutrino mass generation, which predicts the reactor neutrino angle to be 13 % 0:14 close to the recent results from the Daya Bay and RENO experiments. The model predicts also values of the solar and atmospheric neutrino mixing angles, which are compatible with the existing data. The T 0 breaking leads to tribimaximal mixing in the neutrino sector, which is perturbed by sizeable corrections from the charged lepton sector. The model exhibits geometrical CP violation, where all complex phases have their origin from the complex Clebsch-Gordan coefficients of T 0 . The values of the Dirac and Majorana CP violating phases are predicted. For the Dirac phase in the standard parametrization of the neutrino mixing matrix we get a value close to 90 : ffi =2 À 0:45 c ffi 84:3 , c being the Cabibbo angle. The neutrino mass spectrum can be with normal ordering (2 cases) or inverted ordering. In each case the values of the three light neutrino masses are predicted with relatively small uncertainties, which allows one to get also unambiguous predictions for the neutrinoless double beta decay effective Majorana mass.
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