1,194 research outputs found
Two-gluon coupling and collider phenomenology of color-octet technirho mesons
It has recently been suggested that gauge invariance forbids the coupling of
a massive color-octet vector meson to two gluons. While this is true for
operators in an effective Lagrangian of dimension four or less, we demonstrate
that dimension six interactions will lead to such couplings. In the case of
technicolor, the result is a technirho-gluon-gluon coupling comparable to the
naive vector meson dominance estimate, but with a substantial uncertainty. This
has implications for several recent studies of technicolor phenomenology.Comment: 6 pages, LaTeX; added a referenc
Limitations of B-meson mixing bounds on technicolor theories
Recent work by Burdman, Lane, and Rador has shown that B-meson mixing places
stringent lower bounds on the masses of topgluons and Z' bosons in classic
topcolor-assisted technicolor (TC2) models. This paper finds analogous limits
on the Z' bosons of flavor-universal TC2 and non-commuting extended technicolor
models, and compares the limits with those from precision electroweak
measurements. A discussion of the flavor structure of these models (contrasted
with that of classic TC2) shows that B-meson mixing is a less reliable probe of
these models than of classic TC2.Comment: 6 pages, LaTeX; added a reference; added references and discussio
Dijet Mass Spectrum Limits on Flavor-Universal Colorons
Using recent D0 data on the dijet mass spectrum, we present a limit on
flavor-universal colorons. At 95% CL we find Mc/cot(theta) > 837 GeV. We
discuss the implications of this limit for models of quark compositeness,
non-standard gluon interactions, and dynamical electroweak symmetry breaking.
In addition, we place a lower bound Lambda_A8 > 2.1 TeV on the scale of
color-octet axial-vector contact interactions among quarks which could arise in
models of quark compositeness.Comment: 8 pages, 3 figure
b \rightarrow s \gamma AND Z \rightarrow b \overline{b} IN TECHNICOLOR WITH SCALARS
We consider the radiative decay , and the correction
to the vertex in technicolor models with scalars. In these
models, the scalar develops a vacuum expectation value when the technifermions
condense, and the ordinary fermions develop masses via Yukawa couplings. Since
the symmetry breaking sector involves both a fundamental scalar doublet and an
isotriplet of composite scalars (the technipions), the phenomenology associated
with the charged scalars is similar to that found in a type-I two-Higgs doublet
model. We show that the correction to the vertex is small over
the allowed parameter space of the model in the two limits that we consider,
and that there can be large, potentially observable, contributions to the
branching fraction.Comment: 9pp. LaTeX, 4 figures in a uuencoded compressed .ps file We remove
nonstandard LaTeX fonts from the previous versio
Finding Z' bosons coupled preferentially to the third family at CERN LEP and the Fermilab Tevatron
Z' bosons that couple preferentially to the third generation fermions can
arise in models with extended weak (SU(2)xSU(2)) or hypercharge (U(1)xU(1))
gauge groups. We show that existing limits on quark-lepton compositeness set by
the LEP and Tevatron experiments translate into lower bounds of order a few
hundred GeV on the masses of these Z' bosons. Resonances of this mass can be
directly produced at the Tevatron. Accordingly, we explore in detail the limits
that can be set at Run II using the process p pbar -> Z' -> tau tau -> e mu. We
also comment on the possibility of using hadronically-decaying taus to improve
the limits.Comment: LaTeX2e, 24 pages (including title page), 13 figures; version 2:
corrected typographical errors and bad figure placement; version 3: added
references and updated introduction; version 4: changes to compensate for old
latex version on arXiv server; version 5: additional references, and embedded
fonts in eps files for PRD; version 6: corrected some minor typos to address
PRD referee's comment
Meeting irrigation demands in a water-challenged environment
Presented at Meeting irrigation demands in a water-challenged environment: SCADA and technology: tools to improve production: a USCID water management conference held on September 28 - October 1, 2010 in Fort Collins, Colorado.Includes bibliographical references.Accurate estimates of spatially distributed evapotranspiration (ET) using remote sensing inputs could help improve crop water management, the assessment of regional drought conditions, irrigation efficiency, ground water depletion, and the verification of the use of water rights over large irrigated areas. In this study, ET was mapped using surface reflectance and radiometric temperature images from the Landsat 5 satellite in a surface energy budget algorithm driven by a surface aerodynamic temperature (SAT_ET) model. The SAT_ET model was developed using surface temperature, horizontal wind speed, air temperature and crop biophysical characteristic measured over an irrigated alfalfa field in Southeastern Colorado. Estimates of the remote sensing-based ET for a 4.0 hectare alfalfa field and a 3.5 hectare oats field, during the 2009 cropping season, were evaluated using two monolithic weighing lysimeters located at the Colorado State University Arkansas Valley Research Center (AVRC) in Rocky Ford, Colorado. Although the overall model performance was encouraging, results indicated that the SAT_ET model performed well under dry atmospheric and soil conditions and less accurately under high air relative humidity and soil water content conditions. These findings are evidence that SAT_ET needs to be further developed to perform better under a range of environmental and atmospheric conditions
The Collider Phenomenology of Technihadrons in the Technicolor Straw Man Model
We discuss the phenomenology of the lightest SU(3)_C singlet and non-singlet
technihadrons in the Straw Man Model of low-scale technicolor (TCSM). The
technihadrons are assumed to be those arising in topcolor--assisted technicolor
models in which topcolor is broken by technifermion condensates. We improve
upon the description of the color--singlet sector presented in our earlier
paper introducing the TCSM (hep-ph/9903369). These improvements are most
important for subprocess energies well below the masses of the technirho and
techniomega, and, therefore, apply especially to e+e- colliders such as LEP and
a low--energy linear collider. In the color--octet sector, we consider mixing
of the gluon, the coloron V_8 from topcolor breaking, and four isosinglet
color--octet technirho mesons. We assume, as expected in walking technicolor,
that these technirhos decay into qbar-q, gg, and g-technipion final states, but
not into technipion pairs. All the TCSM production and decay processes
discussed here are included in the event generator Pythia. We present several
simulations appropriate for the Tevatron Collider, and suggest benchmark model
lines for further experimental investigation.Comment: 42 pages, 7 figure
Composite Scalars at LEP: Constraining Technicolor Theories
LEPI and LEPII data can be used to constrain technicolor models with light,
neutral pseudo-Nambu-Goldstone bosons, Pa. We use published limits on branching
ratios and cross sections for final states with photons, large missing energy,
jet pairs, and b bbar pairs to constrain the anomalous Pa Z0 Z0, Pa Z0 photon,
and Pa photon photon couplings. From these results, we derive bounds on the
size of the technicolor gauge group and the number of technifermion doublets in
models such as Low-scale Technicolor.Comment: 27 pages (including title page), 15 figures, 6 tables. version 2: In
addressing PRD referee comments, we have significantly expanded our
manuscript, to include detailed discussion of limits from LEP II data, as
well as expanding the number or specific models to which we apply our
results. As a result, we have changed the title from "Z0 decays to composite
scalars: constraining technicolor theories
Resonant and Non-Resonant Effects in Photon-Technipion Production at Lepton Colliders
Lepton collider experiments can search for light technipions in final states
made striking by the presence of an energetic photon: e+e- \to
\photon\technipion. To date, searches have focused on either production
through anomalous coupling of the technipions to electroweak gauge bosons or on
production through a technivector meson (\technirho, \techniomega) resonance.
This paper creates a combined framework in which both contributions are
included. This will allow stronger and more accurate limits on technipion
production to be set using existing data from LEP or future data from a
higher-energy linear collider. We provide explicit formulas and sample
calculations (analytic and Pythia) in the framework of the Technicolor Straw
Man Model, a model that includes light technihadrons.Comment: 11 pages, including title page, 3 figures; version 2: references
adde
Flavour Universal Dynamical Electroweak Symmetry Breaking
The top condensate see-saw mechanism of Dobrescu and Hill allows electroweak
symmetry to be broken while deferring the problem of flavour to an electroweak
singlet, massive sector. We provide an extended version of the singlet sector
that naturally accommodates realistic masses for all the standard model
fermions, which play an equal role in breaking electroweak symmetry. The models
result in a relatively light composite Higgs sector with masses typically in
the range of (400-700)~GeV. In more complete models the dynamics will
presumably be driven by a broken gauged family or flavour symmetry group. As an
example of the higher scale dynamics a fully dynamical model of the quark
sector with a GIM mechanism is presented, based on an earlier top condensation
model of King using broken family gauge symmetry interactions (that model was
itself based on a technicolour model of Georgi). The crucial extra ingredient
is a reinterpretation of the condensates that form when several gauge groups
become strong close to the same scale. A related technicolour model of Randall
which naturally includes the leptons too may also be adapted to this scenario.
We discuss the low energy constraints on the massive gauge bosons and scalars
of these models as well as their phenomenology at the TeV scale.Comment: 22 pages, 3 fig
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