The Top Quark: Experimental Roots and Branches of Theory

The CDF and D0 experiments at the Fermilab Tevatron have discovered the top quark and provided first measurements of many of its properties. The small top sample gathered by Run I leaves open many possibilities for top physics beyond the standard model. Run II and the LHC (and eventually an LC) promise to deepen our knowledge of the top quark and its relationship to electroweak symmetry breaking.Comment: 14 pages, 9 figures; talk presented at HCP200

Top Theories

As the most recently discovered and heaviest quark, the top presents us with theoretical challenges. How are we to understand its properties within the larger effort to explain the origins of electroweak and flavor symmetry breaking ? This talk discusses some of the surprises the top quark may have in store for us and indicates how experiment may help us pinpoint the truth about top.Comment: 17 pages, 15 figures, Talk presented at Heavy Flavours 8, University of Southampton, England, July 25-29, 199

Anomalous Gluon Self-Interactions and ttˉt \bar{t} Production

Strong-interaction physics that lies beyond the standard model may conveniently be described by an effective Lagrangian. The only genuinely gluonic CP-conserving term at dimension six is the three-gluon-field-strength operator $G^3$. This operator, which alters the 3-gluon and 4-gluon vertices form their standard model forms, turns out to be difficult to detect in final states containing light jets. Its effects on top quark pair production hold the greatest promise of visibility.Comment: Latex file using [aps,aipbook,floats,epsf]{revtex}. 12 pages, 4 Postscript figures. Full PS copy at http://smyrd.bu.edu/htfigs/htfigs.html Talk presented by EHS at the International Symposium on Vector Boson Self-Interactions, UCLA, Feb. 1-3, 199

Electroweak Limits on Non-Universal Z' Bosons

Many types of physics beyond the standard model include an extended electroweak gauge group. If these extensions are associated with flavor symmetry breaking, the gauge interactions will not be flavor-universal. In this note we update the bounds placed by electroweak data on the existence of flavor non-universal extensions to the standard model in the context of topcolor assisted technicolor (TC2), noncommuting extended technicolor (NCETC), and the ununified standard model (UUM). In the first two cases the extended gauge interactions couple to the third generation fermions differently than to the light fermions, while in the ununified standard model the gauge interactions couple differently to quarks and leptons. The extra SU(2) triplet of gauge bosons in NCETC and UUM models must be heavier than about 3 TeV, while the extra Z boson in TC2 models must be heavier than about 1 TeV.Comment: 17 pages, 5 figures; added references; updated figure

Testing Extended Technicolor With RbR_b

We review the connection between $m_t$ and the $Zb\bar b$ vertex in ETC models and demonstrate the power of the resulting experimental constraint on models with weak-singlet ETC bosons. Some efforts to bring ETC models into agreement with experimental data on the $Zb\bar b$ vertex are mentioned, and the most promising one (non-commuting ETC) is discussed in detail.Comment: Talk given by E.H. Simmons at the Yukawa International Seminar `95 in Kyoto, 21-26 August, 1995 and at the International Symposium on Heavy Flavor and Electroweak Theory in Beijing, 17-19 August, 1995. Latex (uses PTPTeX.sty and epsf). 9 pages. 1 figure. Full postscript version available at http://smyrd.bu.edu/ . (minor typos corrected

Colorons: Theory and Phenomenology

We briefly describe the structure and phenomenology of a flavor-universal extension of the strong interactions, focusing on the color-octet of massive gauge bosons (`colorons') present in the low-energy spectrum. We discuss current limits on the colorons and what future measurements may reveal

Custodial Symmetry, Flavor Physics, and the Triviality Bound on the Higgs Mass

The triviality of the scalar sector of the standard one-doublet Higgs model implies that this model is only an effective low-energy theory valid below some cut-off scale Lambda. We show that the experimental constraint on the amount of custodial symmetry violation implies that the scale Lambda must be greater than of order 7.5 TeV. The underlying high-energy theory must also include flavor dynamics at a scale of order Lambda or greater in order to give rise to the different Yukawa couplings of the Higgs to ordinary fermions. This flavor dynamics will generically produce flavor-changing neutral currents. We show that the experimental constraints on the neutral D-meson mass difference imply that Lambda must be greater than of order 21 TeV. For theories defined about the infrared-stable Gaussian fixed-point, we estimate that this lower bound on Lambda yields an upper bound of approximately 460 GeV on the Higgs boson's mass, independent of the regulator chosen to define the theory. We also show that some regulator schemes, such as higher-derivative regulators, used to define the theory about a different fixed-point are particularly dangerous because an infinite number of custodial-isospin-violating operators become relevant.Comment: 15 pages, 7 ps/eps embedded figures, talk presented at the 1996 International Workshop on Perspectives of Strong Coupling Gauge Theories (SCGT 96), Nagoya, Japa

Testing Extended Technicolor with R_b and Single Top Quark Production

We review the connection between m_t and the $Zb\bar b$ vertex in ETC models and discuss how data on R_b constrains ETC models. Theories in which the ETC and weak gauge groups do not commute are consistent with electroweak data and predict effects on single top production that will be visible at Fermilab.Comment: 8 pages, 2 figures; Talk given at Ringberg Workshop on The Higgs Puzzle, 8-13 December 199

Higgsless Models: Lessons from Deconstruction

This talk reviews recent progress in Higgsless models of electroweak symmetry breaking, and summarizes relevant points of model-building and phenomenology.Comment: 12 pages, 2 figures, Presented at the X Mexican Workshop on Particles and Field

The Top Triangle Moose

We introduce a deconstructed model that incorporates both Higgsless and top-color mechanisms. The model alleviates the typical tension in Higgsless models between obtaining the correct top quark mass and keeping delta-rho small. It does so by singling out the top quark mass generation as arising from a Yukawa coupling to an effective top-Higgs which develops a small vacuum expectation value, while electroweak symmetry breaking results largely from a Higgsless mechanism. As a result, the heavy partners of the SM fermions can be light enough to be seen at the LHC.Comment: To appear in proceedings of SCGT09, Nagoya, Japan. 5 page