Bosonic Topcolor

A topcolor model is presented that contains both composite and fundamental scalar fields. Strong dynamics accounts for most of the top quark mass and part of the electroweak symmetry breaking scale. The fundamental scalar is weakly coupled and transmits its share of electroweak symmetry breaking to the light fermions. The model is allowed by the current experimental bounds, and can give a potentially large contribution to $D^0-\bar{D^0}$ mixing.Comment: Talk given by A. Aranda at DPF 2000, Ohio State, August 200

Eigenstructure Assignment Based Controllers Applied to Flexible Spacecraft

The objective of this paper is to evaluate the behaviour of a controller designed using a parametric Eigenstructure Assignment method and to evaluate its suitability for use in flexible spacecraft. The challenge of this objective lies in obtaining a suitable controller that is specifically designated to alleviate the deflections and vibrations suffered by external appendages in flexible spacecraft while performing attitude manoeuvres. One of the main problems in these vehicles is the mechanical cross-coupling that exists between the rigid and flexible parts of the spacecraft. Spacecraft with fine attitude pointing requirements need precise control of the mechanical coupling to avoid undesired attitude misalignment. In designing an attitude controller, it is necessary to consider the possible vibration of the solar panels and how it may influence the performance of the rest of the vehicle. The nonlinear mathematical model of a flexible spacecraft is considered a close approximation to the real system. During the process of controller evaluation, the design process has also been taken into account as a factor in assessing the robustness of the system

Bounds on Bosonic Topcolor

We consider the phenomenology of models in which electroweak symmetry breaking is triggered by new strong dynamics affecting the third generation and is transmitted to the light fermions via a fundamental Higgs doublet. While similar in spirit to the old bosonic technicolor idea, such `bosonic topcolor' models are allowed by current phenomenological constraints, and may arise naturally in models with large extra dimensions. We study the parameter space of a minimal low-energy theory, including bounds from Higgs boson searches, precision electroweak parameters, and flavor changing neutral current processes. We show that the model can provide a contribution to D0-D0-bar mixing as large as the current experimental bound.Comment: 16 pages RevTeX, 3 Figure

A Lot of Flavor Physics from a Little Symmetry

Recent neutrino parameter measurements place increasingly stringent constraints on acceptable supersymmetric theories of flavor. A very fruitful approach is the application of non-Abelian discrete gauged flavor symmetries G_f. We discuss a highly successful model using G_f = T' x Z_3, where T' is a non-Abelian group based on the symmetries of a tetrahedron. This model reproduces the basic features of the U(2) model, and also predicts neutrino masses and mixing angles consistent with either the SMA or LMA solutions.Comment: 3 pages Latex. Talk presented by R.F. Lebed at DPF 2000, Ohio State U., Columbus, OH, 9--12 Aug. 200

Higher-dimensional Higgs Representations in SGUT models

Supersymmetric Grand Unified Theories (SGUTs) have achieved some degree of success, already present in the minimal models (with SU(5) or SO(10)). However, there are open problems that suggest the need to incorporate more elaborate constructions, specifically the use of higher-dimensional representations in the Higgs sector. For example, a $45$ representation of SU(5) is often included to obtain correct mass relations for the first and second families of d-type quarks and leptons. When one adds these higher-dimensional Higgs representations one must verify the cancellation of anomalies associated to their fermionic partners. One possible choice, free of anomalies, include both $45,\overline{45}$ representations to cancel anomalies. We review the necessary conditions for the cancellation of anomalies and discuss the different possibilities for supersymmetric SU(5) models. Alternative anomaly-free combinations of Higgs representations, beyond the usual vectorlike choice, are identified, and it is shown that their corresponding $\beta$ functions are not equivalent. Although the unification of gauge couplings is not affected, the introduction of multidimensional representations leads to different scenarios for the perturbative validity of the theory up to the Planck scale. We study the effect on the evolution of the gauge coupling up to the Planck scale due to the different sets of fields and representations that can render an anomaly-free model.Comment: 6 pages, 3 figures. Presented by ADR at the Dark Side of the Universe Conference, Leon, Gto. Mexico 201