| The Standard Model (SM) of elementary particles is a theoretical model that describes quite accurately what seem to be the constituents of matter and the forces that govern their dynamics, with the exception of gravity. Our confidence in the validity of the SM lies in experimental results obtained in accelerator experiments that, up to now, have not contradicted it in a radical way. One of the shortcomings of the SM from a theoretical point of view is that it has many parameters input "by hand." These are parameters that are necessary for its consistency but their origin is unknown. However, what we would like to call the real model of nature is one where all the parameters are self determined dynamically rather than put by hand. In addition, theoretical investigations of its underlying mathematical structure, as well as attempts to extend the model so that it includes gravity, revealed certain inconsistencies at energy scales far above our current experimental capabilities and led to the conclusion that the SM is probably correct but not complete; it has to be complemented by additional structure. One of the most popular such extensions is a new symmetry, so called supersymmetry, that provides a theoretically promising candidate that can solve many of these problems and it is consistent with the only consistent quantum gravity theory, M theory. The model in this thesis is, to our knowledge, the first which has these characteristics. First, it provides a scheme that can explain the origin of most of the arbitrary parameters of the SM, it is supersymmetric and it naturally predicts properties of elementary particles that will be tested very soon in experimental laboratories. Two of the most striking examples of such predictions are the masses and the mixing properties of neutrinos and the mass of the only particle that is believed to be elementary in the SM but it has not been experimentally detected yet: the Higgs particle. Second, it is a model that has many of the signature features of models that come directly from string theory (M theory) compactifications. We would like to stress the fact that since the model we are presenting here is not a direct descendant of a string theory, it can not be viewed as a fundamental theory but rather as a phenomenological extension of the SM that could come from a string theory. Given the fact that up this day we are not sure if string theory is the relevant mathematical description of the universe and that no viable "string compactification" has been constructed yet, this model not only proposes a simple link between the exotic string theories that live at huge energy scales and our experimentally reachable world, but also provides a possible guide to those who are hoping to prove that string theory is correct by showing that the SM naturally emerges after compactifying a string theory to four dimensions---a highly non trivial and non unique process. |
