2,495 research outputs found
Technifermion Representations and Precision Electroweak Constraints
We discuss the selection of fermion representations in technicolor models
with a view toward minimizing technicolor contributions to the precision
electroweak parameter. We present and analyze models that involve one
technifermion SU(2) doublet with standard-model singlet technifermion
sectors that lead to walking behavior, which further reduces . We also
consider models that have technifermions in higher-dimensional representations
and study embeddings in extended technicolor theories.Comment: 8 pages, late
Quark Dipole Operators in Extended Technicolor Models
We study diagonal and transition quark dipole operators in a class of
extended technicolor (ETC) models, taking account of the multiscale nature of
the ETC gauge symmetry breaking and of the mixing among ETC interaction
eigenstates. Because of this mixing, terms involving the lowest ETC scale can
play an important role in dipole operators, and we focus on these terms. We
derive from experiment new correlated constraints on the quark mixing angles
and phases. Our bounds yield information on mixing angles individually in the
up- and down-sectors, for both left- and right-handed quark fields and thus
constrain even quark mixing parameters that do not enter in the CKM matrix.
With phases of order unity, we conclude that these mixing angles are small,
constraining future ETC model building, but plausibly in the range suggested by
the size of the CKM elements. These values still allow substantial deviations
from the standard model predictions, in particular for several CP violating
quantities, including the asymmetries in and , , and the electric dipole moments of the
neutron and the Hg atom.Comment: 9 pages, late
Neutrino Masses in Theories with Dynamical Electroweak Symmetry Breaking
We address the problem of accounting for light neutrino masses in theories
with dynamical electroweak symmetry breaking. We discuss this in the context of
a class of (extended) technicolor (ETC) models and analyze the full set of
Dirac and Majorana masses that arise in such theories. As a possible solution,
we propose a combination of suppressed Dirac masses and a seesaw involving
dynamically generated condensates of standard-model singlet,
ETC-nonsinglet fermions. We show how this can be realized in an explicit ETC
model. An important feature of this proposal is that, because of the
suppression of Dirac neutrino mass terms, a seesaw yielding realistic neutrino
masses does not require superheavy Majorana masses; indeed, these Majorana
masses are typically much smaller than the largest ETC scale.Comment: 13 pages, latex; simplified mode
Lepton Dipole Moments in Extended Technicolor Models
We analyze the diagonal and transition magnetic and electric dipole moments
of charged leptons in extended technicolor (ETC) models, taking account of the
multiscale nature of the ETC gauge symmetry breaking, conformal (walking)
behavior of the technicolor theory, and mixing in the charged-lepton mass
matrix. We show that mixing effects dominate the ETC contributions to charged
lepton electric dipole moments and that these can yield a value of |d_e|
comparable to the current limit. The rate for mu to e gamma can also be close
to its limit. From these and other processes we derive constraints on the
charged lepton mixing angles. The constraints are such that the ETC
contribution to the muon anomalous magnetic moment, which includes a
significant lepton mixing term, can approach, but does not exceed, the current
sensitivity level.Comment: 4 pages, revte
Maximum Wavelength of Confined Quarks and Gluons and Properties of Quantum Chromodynamics
Because quarks and gluons are confined within hadrons, they have a maximum
wavelength of order the confinement scale. Propagators, normally calculated for
free quarks and gluons using Dyson-Schwinger equations, are modified by
bound-state effects in close analogy to the calculation of the Lamb shift in
atomic physics. Because of confinement, the effective quantum chromodynamic
coupling stays finite in the infrared. The quark condensate which arises from
spontaneous chiral symmetry breaking in the bound state Dyson-Schwinger
equation is the expectation value of the operator evaluated in the
background of the fields of the other hadronic constituents, in contrast to a
true vacuum expectation value. Thus quark and gluon condensates reside within
hadrons. The effects of instantons are also modified. We discuss the
implications of the maximum quark and gluon wavelength for phenomena such as
deep inelastic scattering and annihilation, the decay of heavy quarkonia, jets,
and dimensional counting rules for exclusive reactions. We also discuss
implications for the zero-temperature phase structure of a vectorial SU()
gauge theory with a variable number of massless fermions.Comment: 6 pages, late
The Zero Temperature Chiral Phase Transition in SU(N) Gauge Theories
We investigate the zero temperature chiral phase transition in an SU(N) gauge
theory as the number of fermions is varied. We argue that there exists a
critical number of fermions , above which there is no chiral symmetry
breaking or confinement, and below which both chiral symmetry breaking and
confinement set in. We estimate and discuss the nature of the phase
transition.Comment: 13 pages, LaTeX, version published in PR
Chiral phase transition at finite temperature and conformal dynamics in large Nf QCD
We investigate the chiral phase transition at finite temperature (T) in
colour SU(Nc=3) Quantum Chromodynamics (QCD) with six species of fermions
(Nf=6) in the fundamental representation by using lattice QCD with improved
staggered fermions. By considering lattices with several temporal extensions
Nt, we observe asymptotic scaling for Nt > 4. We then extract the dimensionless
ratio Tc/Lambda_L (Lambda_L = Lattice Lambda-parameter) for Nf = 6 and Nf = 8,
the latter relying on our earlier results. Further, we collect the critical
couplings beta^c for the chiral phase transition at Nf = 0 (quenched), and Nf =
4 at a fixed Nt = 6. The results are consistent with enhanced fermionic
screening at larger Nf. The Tc/Lambda_L depends very mildly on Nf in the Nf = 0
- 4 region, starts increasing at Nf = 6, and becomes significantly larger at Nf
= 8, close to the edge of the conformal window. We discuss interpretations of
these results as well as their possible interrelation with preconformal
dynamics in the light of a functional renormalization group analysis.Comment: 8 pages, 9 figure
A Realistic Technicolor Model from 150 TeV down
A realistic technicolor model is presented with the dynamics below TeV
treated explicitly. Electroweak symmetry is broken by the condensates of a
`minimal' doublet of technifermions. The new feature of the model is that the
the third generation quarks are unified with the technifermions into multiplets
of a walking gauge force down to a scale of TeV. The remaining quarks and
leptons are not involved in this unification however. The walking dynamics
enhances the higher dimension interactions which give the ordinary fermions
their masses and mixing, while leaving flavor-changing neutral currents
suppressed. Because the third generation quarks actually feel the walking force
their masses can be much larger than those of the other quarks and the leptons.
The only non-standard particles with masses below several TeV are the single
doublet of technifermions, so electroweak radiative corrections are estimable
and within experimental limits.Comment: 21 page
Multiscale Technicolor and Top Production
Pair-production of heavy top quarks at the Tevatron Collider is significantly
enhanced by the color--octet technipion, , occurring in multiscale
models of walking technicolor. We discuss rates for GeV
and GeV. Multiscale models also have color--octet
technirho states in the mass range 200-600 GeV that appear as resonances in
dijet production and technipion pair--production.Comment: 12 pages (plain TeX) and 4 figures (uuencoded),
FERMILAB--PUB--94/007-T and BUHEP-94-
A condition on the chiral symmetry breaking solution of the Dyson-Schwinger equation in three-dimensional QED
In three-dimensional QED, which is analyzed in the 1/ expansion, we obtain
a sufficient and necessary condition for a nontrivial solution of the
Dyson-Schwinger equation to be chiral symmetry breaking solution. In the
derivation, a normalization condition of the Goldstone bound state is used. It
is showed that the existent analytical solutions satisfy this condition.Comment: 11 pages, Latex, no figures, accepted by Phys.Lett.
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