R.S. Chivukula

New strong interactions at the Tevatron

Abstract Recent results from CDF indicate that the inclusive cross section for jets with E r > 200 GeV is significantly higher than that predicted by QCD. We describe here a simple flavor-universal variant of the “coloron” model of Hill and Parke that can accommodate such a jet excess, and which is not in contradiction with other experimental data. As such, the model serves as a useful baseline with which to compare both the data and other models proposed to describe the jet excess. An interesting theoretical feature of the model is that if the global chiral symmetries of the quarks remain unbroken in the confining phase of the coloron interaction, it realizes the possibility that the ordinary quarks are composite particles.

A heavy top quark and the Zbb vertex in non-commuting extended technicolor

Abstract We explore corrections to electroweak parameters in the context of Extended Technicolor (ETC) models in which the ETC gauge-boson which generates the top-quark mass carries weak SU(2) charge. For mt≈150 GeV there exist potentially large corrections to the Z decay width to b-quarks. Interestingly, in contrast to the situation in ETC models where the gauge-boson which generates the top-quark mass is a weak SU(2) singlet, the corrections may increase the Z→b b branching ratio.

Electroweak limits on nonuniversal Z-prime bosons

Author(s): Chivukula, RS; Simmons, EH | Abstract: 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.

Limits on noncommuting extended technicolor.

Using precision electroweak data, we put limits on noncommuting extended technicolor models. We conclude that these models are viable only if the ETC interactions are strong. Interestingly, these models predict a pattern of deviations from the standard model which can fit the data significantly better than the standard model does, even after taking into account the extra parameters involved. {copyright} {ital 1996 The American Physical Society.}

Isospin breaking and fine-tuning in top-color assisted technicolor

Recently, Hill has proposed a model in which new, potentially low-energy, top-color interactions produce a top-condensate (a la Nambu-Jona-Lasinio) and accommodate a heavy top quark, while technicolor is responsible for producing the W and Z masses. Here we argue that isospin breaking gauge interactions, which are necessary in order to split the top and bottom quark masses, are likely to couple to technifermions. In this case they produce a significant shift in the W and Z masses (i.e. contribute to Δϱ∗ = αT) if the scale of the new interactions is near 1 TeV. In order to satisfy experimental constraints on Δϱ∗, we find that either the effective top quark coupling or the top-color coupling must be adjusted to 1%. Independent of the couplings of the technifermions, we show that the isospin-splitting of the top and bottom quarks implies that the top-color gauge bosons must have masses larger than about 1.4 TeV. Our analysis can also be applied to strong extended technicolor (ETC) models that produce the top-bottom splitting via isospin breaking ETC interactions.

Walking technicolor and the Zbb vertex

Abstract A slowly running technicolor coupling will affect the size of non-oblique corrections to the Zb b vertex from extended technicolor dynamics. We show that, while “walking technicolor” reduces the magnitude of the corrections, they generally remain large enough to be seen at LEP.

Analyticity, crossing symmetry and the limits of chiral perturbation theory

The chiral Lagrangian for Goldstone-boson scattering is a power-series expansion in numbers of derivatives. Each successive term is suppressed by powers of a scale, Λ χ , which must be less than of order 4πf/√N where f is the Goldstone-boson decay constant and N is the number of flavors. The chiral expansion therefore breaks down at or below 4πf/√N. Because of crossing symmetry, some «isospin» channels will deviate from their low-energy behavior well before they approach the scale at which their low-energy amplitudes would violate unitarity. The breakdown of the chiral expansion is associated with the appearance of physical states other than Goldstone bosons

Precision electroweak constraints on top-color assisted technicolor

Using precision electroweak data, we put limits on “natural” top-color assisted technicolor models. Generically the new U(1) gauge bosons in these models must have masses larger than roughly 2 TeV, although in certain (seemingly unrealistic) models the bound can be much lower.

Limits on the ununified standard model

Abstract The ununified standard model is an extension of the standard model that contains separate electroweak gauge groups for quarks and leptons. When it was originally proposed, data allowed the new gauge bosons to be quite light. We use recent data from precision electroweak measurements to put stringent bounds on the ununified standard model. In particular, at the 95% confidence level, we find that the ununified gauge bosons must have masses above about 2 TeV.

Theory of a strongly interacting electroweak symmetry breaking sector

Author(s): Chivukula, RS; Dugan, MJ; Golden, M; Simmons, EH | Abstract: In this review we discuss theories of the electroweak-symmetry-breaking sector in which the W and Z interactions become strong at an energy scale not larger than a few TeV.