603 research outputs found

### 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 $R_b$

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

### Condensate Enhancement and D-Meson Mixing in Technicolor Theories

Since the pioneering work of Eichten and Lane it has been known that the
scale of the interactions responsible for the generation of the strange-quark
mass in extended technicolor theories must, absent any "GIM-like" mechanism for
suppressing flavor-changing neutral currents, be greater than of order 1000
TeV. In this note we point out that the constraint from the neutral D-meson
system is now equally strong, implying that the charm quark mass must also
arise from flavor dynamics at a scale this high. We then quantify the degree to
which the technicolor condensate must be enhanced in order to yield the
observed quark masses, if the extended technicolor scale is of order 1000 TeV.
Our results are intended to provide a framework in which to interpret and apply
the results of lattice studies of conformal strongly interacting gauge
theories, and the corresponding numerical measurements of the anomalous
dimension of the mass operator in candidate theories of "walking" technicolor.Comment: 6 pages, references added and re-ordere

### 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

### The structure of electroweak corrections due to extended gauge symmetries

This paper studies models with extended electroweak gauge sectors of the form
SU(2) x SU(2) x U(1) x [SU(2) or U(1)]. We establish the general behavior of
corrections to precision electroweak observables in this class of theories and
connect our results to previous work on specific models whose electroweak
sectors are special cases of our extended group.Comment: 18 pages, 2 figures; added a referenc

### 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

### Production of Massive Color-Octet Vector Bosons at Next-to-Leading Order

We report the first complete calculation of QCD corrections to the production
of a massive color-octet vector boson. Our next-to-leading-order (NLO)
calculation includes both virtual corrections as well as corrections arising
from the emission of gluons and light quarks, and we demonstrate the reduction
in factorization-scale dependence relative to the leading-order approximation
used in previous hadron collider studies. We show that the QCD NLO corrections
to coloron production are as large as 30%, and that the residual factorization
scale-dependence is reduced to of order 2%. We also calculate the K-factor and
the p_T spectrum for coloron production, since these are valuable for
comparison with experiment. Our results apply directly to the production of the
massive color-octet vector bosons in axigluon, topcolor, and coloron models,
and approximately to the production of KK gluons in extra-dimensional models or
color-octet technivector mesons in technicolor models.Comment: 23 pages, 35 pdf figures included. Added discussion of PT spectrum,
tables of values of K-factor, and reference

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