| We introduce the standard model (SM) of elementary particles and show that it is afflicted by a large fine tuning of the tree level Higgs mass parameter. We solve this problem by eliminating the Higgs scalar from the theory and defining a Higgsless model based on an SU(2) N+1 x U(1) gauge symmetry. We show that the scale of unitarity violation of the new theory is higher than that of the SM without the Higgs, and we show that the new model satisfies the electroweak experimental constraints.;We determine model-independent constraints on new physics contributions from precision electroweak measurements. We then test the viability of top-color assisted technicolor models using these constraints, and find that one of the models studied is indeed consistent with the experimental results.;We introduce a simple extension of the SM which implements custodial symmetry, that protects electroweak observables from large corrections, in a top-quark mass generation sector of the Lagrangian. We then study the phenomenological viability of the model, and show that the new physics gives an unusual negative contribution to one of the electroweak parameters.;Finally, we study the consequences of a noncommutative space, which is characterized by a non-zero minimal measurable distance, on the particle physics phenomenology. We study e+e - gammagammagamma scattering in noncommutative quantum electrodynamics at future colliders, and extract lower limits on space noncommutativity in function of cross sections relative to that process. |
