440 research outputs found
Z Boson Propagator Correction in Technicolor Theories with ETC Effects Included
We calculate the Z boson propagator correction, as described by the S
parameter, in technicolor theories with extended technicolor interactions
included. Our method is to solve the Bethe-Salpeter equation for the requisite
current-current correlation functions. Our results suggest that the inclusion
of extended technicolor interactions has a relatively small effect on S.Comment: 15pages, 8 figure
Reduction techniques of the back gate effect in the SOI Pixel Detector
We have fabricated monolithic pixel sensors in 0.2 μm Silicon-On-Insulator (SOI) CMOS technology, consisting of a thick sensor layer and a thin circuit layer with an insulating buried-oxide, which has many advantages. However, it has been found that the applied electric field in the sensor layer also affects the transistor operation in the adjacent circuit layer. This limits the applicable sensor bias well below the full depletion voltage. To overcome this, we performed a TCAD simulation and added an additional p-well (buried pwell) in the SOI process. Designs and preliminary results are presented
Electroweak Corrections and Unitarity in Linear Moose Models
We calculate the form of the corrections to the electroweak interactions in
the class of Higgsless models which can be "deconstructed'' to a chain of SU(2)
gauge groups adjacent to a chain of U(1) gauge groups, and with the fermions
coupled to any single SU(2) group and to any single U(1) group along the chain.
The primary advantage of our technique is that the size of corrections to
electroweak processes can be directly related to the spectrum of vector bosons
("KK modes"). In Higgsless models, this spectrum is constrained by unitarity.
Our methods also allow for arbitrary background 5-D geometry, spatially
dependent gauge-couplings, and brane kinetic energy terms. We find that, due to
the size of corrections to electroweak processes in any unitary theory,
Higgsless models with localized fermions are disfavored by precision
electroweak data. Although we stress our results as they apply to continuum
Higgsless 5-D models, they apply to any linear moose model including those with
only a few extra vector bosons. Our calculations of electroweak corrections
also apply directly to the electroweak gauge sector of 5-D theories with a bulk
scalar Higgs boson; the constraints arising from unitarity do not apply in this
case.Comment: 50 pages, 11 eps figures, typos correcte
2D potential measurements by applying automatic beam adjustment system to heavy ion beam probe diagnostic on the Large Helical Device
Two-dimensional potential profiles in the Large Helical Device (LHD) were measured with heavy ion beam probe (HIBP). To measure the two-dimensional profile, the probe beam energy has to be changed. However, this task is not easy, because the beam transport line of LHD-HIBP sys- tem is very long (?20 m), and the required beam adjustment consumes much time. To reduce the probe beam energy adjustment time, an automatic beam adjustment system has been developed. Us- ing this system, required time to change the probe beam energy is dramatically reduced, such that two-dimensional potential profiles were able to be successfully measured with HIBP by changing the probe beam energy shot to shot
Light flavor-singlet scalars and walking signals in Nf=8 QCD on the lattice
Based on the highly improved staggered quark action, we perform lattice simulations of Nf=8 QCD and confirm our previous observation of a flavor-singlet scalar meson (denoted as σ) as light as the pion and various "walking signals" through low-lying spectra, with higher statistics, smaller fermion masses mf, and larger volumes. We measure Mπ, Fπ, Mρ, Ma0, Ma1, Mb1, MN, Mσ, Fσ, ⟨ψ¯ψ⟩ (both directly and through the GMOR relation), and the string tension. The data are consistent with the spontaneously broken phase of the chiral symmetry, in agreement with the previous results: ratios of the quantities to Mπ monotonically increase in the smaller mf region towards the chiral limit similarly to Nf=4 QCD, in sharp contrast to Nf=12 QCD where the ratios become flattened. The hyperscaling relation holds with roughly a universal value of the anomalous dimension, γm≃1, with a notable exception of Mπ with γm≃0.6 as in the previous results. This is a salient feature ("walking signal") of Nf=8, unlike either Nf=4 which has no hyperscaling relation at all, or Nf=12 QCD which exhibits universal hyperscaling. We further confirm the previous observation of the light σ with mass comparable to the pion in the studied mf region. In a chiral limit extrapolation of the σ mass using the dilaton chiral perturbation theory and also using the simple linear fit, we find the value consistent with the 125 GeV Higgs boson within errors. Our results suggest that the theory could be a good candidate for walking technicolor model, having anomalous dimension γm≃1 and a light flavor-singlet scalar meson as a technidilaton, which can be identified with the 125 GeV composite Higgs in Nf=8 one-family model
Meson masses in large Nf QCD from the Bethe-Salpeter equation
We solve the homogeneous Bethe-Salpeter (HBS) equation for the scalar,
pseudoscalar, vector, and axial-vector bound states of quark and anti-quark in
large Nf QCD with the improved ladder approximation in the Landau gauge. The
quark mass function in the HBS equation is obtained from the Schwinger-Dyson
(SD) equation in the same approximation for consistency with the chiral
symmetry. Amazingly, due to the fact that the two-loop running coupling of
large Nf QCD is explicitly written in terms of an analytic function, large Nf
QCD turns out to be the first example in which the SD equation can be solved in
the complex plane and hence the HBS equation directly in the time-like region.
We find that approaching the chiral phase transition point from the broken
phase, the scalar, vector, and axial-vector meson masses vanish to zero with
the same scaling behavior, all degenerate with the massless pseudoscalar meson.
This may suggest a new type of manifestation of the chiral symmetry restoration
in large Nf QCD.Comment: 33 pages, 16 figures. Typos are corrected. Minor corrections and
references are added. Version to appear in Phys. Rev.
Distinguishing among Technicolor/Warped Scenarios in Dileptons
Models of dynamical electroweak symmetry breaking usually include new spin-1
resonances, whose couplings and masses have to satisfy electroweak precision
tests. We propose to use dilepton searches to probe the underlying structure
responsible for satisfying these. Using the invariant mass spectrum and charge
asymmetry, we can determine the number, parity, and isospin of these
resonances. We pick three models of strong/warped symmetry breaking, and show
that each model produces specific features that reflect this underlying
structure of electroweak symmetry breaking and cancellations.Comment: Added missing referenc
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