Thesis

Quest for a realistic Orbifold Grand Unification

• Call:

  IDPASC Portugal - PHD Programme 2014

• Academic Year:

  2014 /2015

• Domain:

  Theoretical Particle Physics

• Supervisor:

  David Emmanuel-Costa

• Co-Supervisor:

  Ricardo Gonzalez Felipe

• Institution:

  Instituto Superior Técnico

• Host Institution:

  CFTP/IST

• Abstract:

  The idea to unify three of the four interactions observed at low energy, namely the strong, electromagnetic and weak interactions, has attracted many theorists during the last decades. In GUTs not only one get the unification of the gauge couplings but also the Standard Model (SM) fermions belong to larger GUT multiplets. Thus, GUTs models are a beautiful framework for studying fermion masses and their mixings. Because of matter unification, proton decay is one of the direct consequences of grand unification. Another beautiful aspect of many GUT models is the generation of neutrino masses, since neutrinos remain massless in the SM. When such GUT models are realised within the framework of supersymmetry (SUSY) the issue of proton decay is problematic, because new processes (dimension-five operators) involving scalar SUSY partners of the fermions dominate and therefore proton decays faster. Orbifold GUTs can indeed be an attractive solution to this problem. An orbifold is a Higher-dimensional space-time obtained by dividing a manifold with some discrete symmetries, having fixed points, which transform into themselves under the discrete transformations. One of the main features of orbifold compactifications is to allow the breaking of the GUT gauge symmetry to the SM gauge group in an simple way. In particular, the breaking of the GUT symmetry automatically yields to the required doublet- triplet splitting of Higgs fields. Several SU(5) models have been constructed in five dimensions (5d), whereas six dimensions are required for the breaking of SO(10). During this project the student will learn aspects of group theory, fermion masses in GUT framework including extra flavour symmetries, Textures zeroes, Proton decay, CP violation and other aspects of flavour physics. Special emphasis will be given to orbifold SO(10) GUT models in 6D space-time and their phenomenological implications.