495 research outputs found
Extended Iterative Scheme for QCD: Three-point Vertices
In the framework of a generalized iterative scheme introduced previously to
account for the non-analytic coupling dependence associated with the
renormalization-group invariant mass scale Lambda, we establish the
self-consistency equations of the extended Feynman rules (Lambda-modified
vertices of zeroth perturbative order) for the three-gluon vertex, the two
ghost vertices, and the two vertices of massless quarks. Calculations are
performed to one-loop-order, in Landau gauge, and at the lowest approximation
level (r=1) of interest for QCD. We discuss the phenomenon of compensating
poles inherent in these equations, by which the formalism automatically cancels
unphysical poles on internal lines, and the role of composite-operator
information in the form of equation-of-motion condensate conditions. The
observed near decoupling of the four-gluon conditions permits a solution to the
2-and-3-point conditions within an effective one-parameter freedom. There
exists a parameter range in which one solution has all vertex coefficients
real, as required for a physical solution, and a narrower range in which the
transverse-gluon and massless-quark propagators both exhibit complex-conjugate
pole pairs.Comment: 28 pages, 7 figure
A numerical test of the Y-system in the small size limit of the SU(2)x SU(2) Principal Chiral Model
Recently, Kazakov, Gromov and Vieira applied the discrete Hirota dynamics to
study the finite size spectra of integrable two dimensional quantum field
theories. The method has been tested from large values of the size L down to
moderate values using the SU(2) x SU(2) principal chiral model as a theoretical
laboratory. We continue the numerical analysis of the proposed non-linear
integral equations showing that the deep ultraviolet region L -> 0 is
numerically accessible. To this aim, we introduce a relaxed iterative algorithm
for the numerical computation of the low-lying part of the spectrum in the U(1)
sector. We discuss in details the systematic errors involved in the
computation. When a comparison is possible, full agreement is found with
previous TBA computations.Comment: 28 pages, 24 figure
Production of neutral MSSM Higgs bosons in collisions: a complete 1-loop calculation
We present the first complete 1-loop diagrammatic calculation of the cross
sections for the neutral Higgs production processes e^+e^-\ra Z^0h^0 and
e^+e^-\ra A^0h^0 in the minimal supersymmetric standard model. We compare the
results from the diagrammatic calculation with the corresponding ones of the
simpler and compact effective potential approximation and discuss the typical
size of the differences.Comment: LaTeX, 16 pages, 8 figures appended in a uuencoded file, complete
PostScript file available at
http://itpaxp1.physik.uni-karlsruhe.de/prep/KA-TP-16-1995/KA-TP-16-199
Quantum effects on Higgs-strahlung events at Linear Colliders within the general 2HDM
The associated production of neutral Higgs bosons with the Z gauge boson is
investigated in the context of the future linear colliders, such as the ILC and
CLIC, within the general two-Higgs-doublet model (2HDM). We compute the
corresponding production cross-sections at one-loop, in full consistency with
the available theoretical and phenomenological constraints. We find that the
wave-function renormalization corrections to the external Higgs fields are the
dominant source of the quantum effects, which turn out to be large and
negative, and located predominantly in the region around \tan\beta=1 and
moderate values of the parameter \lambda_5 (being \lambda_5 < 0). This behavior
can be ultimately traced back to the enhancement potential of the triple Higgs
boson self-couplings, a trademark feature of the 2HDM with no counterpart in
the Higgs sector of the Minimal Supersymmetric Standard Model. The predicted
Higgs-strahlung rates comfortably reach a few tens of femtobarn, which means
barely 10^3 - 10^4 events per 500 inverse femtobarn of integrated luminosity.
Due to their great complementarity, we argue that the combined analysis of the
Higgs-strahlung events and the previously computed one-loop Higgs-pair
production processes could be instrumental to probe the structure of the Higgs
sector at future linac facilities.Comment: LaTeX, 16 pages, 9 Figures, 2 Tables. Extended discussion, references
added, matches published version in Phys. Rev.
Lightly supervised automatic subtitling of weather forecasts
Since subtitling television content is a costly process, there are large potential advantages to automating it, using automatic speech recognition (ASR). However, training the necessary acoustic models can be a challenge, since the available training data usually lacks verbatim orthographic transcriptions. If there are approximate transcriptions, this problem can be overcome using light supervision methods. In this paper, we perform speech recognition on broadcasts of Weatherview, BBCâs daily weather report, as a first step towards automatic subtitling. For training, we use a large set of past broadcasts, using their manually created subtitles as approximate transcriptions. We discuss and and compare two different light supervision methods, applying them to this data. The best training set finally obtained with these methods is used to create a hybrid deep neural networkbased recognition system, which yields high recognition accuracies on three separate Weatherview evaluation sets
A Comprehensive Model of a Doubly Fed Induction Generator for Dynamic Simulations and
Abstract. The doubly fed induction generator (DFIG) is a very suitable generator type for wind turbine applications. However, its operation principles and its control are rather complex. This paper will describe the different steps for modelling and simulating the generator behaviour. A simulation example of the operation of a DFIG in a small power system is presented
Neutral Higgs-pair production at Linear Colliders within the general 2HDM: quantum effects and triple Higgs boson self-interactions
The pairwise production of neutral Higgs bosons is analyzed in the context of
the future linear colliders, such as the ILC and CLIC, within the general
Two-Higgs-Doublet Model (2HDM). The corresponding cross-sections are computed
at the one-loop level in full compliance with the current phenomenological
bounds and the stringent theoretical constraints inherent to the consistency of
the model. We uncover regions across the 2HDM parameter space, mainly for low
tan\beta near 1 and moderate values of the relevant lambda_5 parameter, wherein
the radiative corrections to the Higgs-pair production cross sections can
comfortably reach 50% This behavior can be traced back to the enhancement
capabilities of the trilinear Higgs self-interactions -- a trademark feature of
the 2HDM, with no counterpart in the Minimal Supersymmetric Standard Model.
Interestingly enough, the quantum effects are positive for energies around 500
GeV, thereby producing a significant enhancement in the expected number of
events precisely around the fiducial startup energy of the ILC. The Higgs-pair
production rates can be substantial, typically amounting to a few thousand
events per 500 inverse femtobarn of integrated luminosity. In contrast, the
corrections are negative in the highest energy range (1 TeV). We also compare
the exclusive pairwise production of Higgs bosons with the inclusive gauge
boson fusion channels leading to 2H+X finals states, and also with the
exclusive triple Higgs boson production. We find that these multiparticle final
states can be highly complementary in the overall Higgs bosons search strategy.Comment: 42 pages, 23 figures, 10 tables. Accepted in Phys. Rev. D (the
published version is shorter
The Higgs Boson Production Cross Section as a Precision Observable?
We investigate what can be learned at a linear collider about the sector of
electroweak symmetry breaking from a precise measurement of the Higgs boson
production cross section through the process e+e- -> hZ. We focus on deviations
from the Standard Model arising in its minimal supersymmetric extension. The
analysis is performed within two realistic future scenarios, taking into
account all prospective experimental errors on supersymmetric particle masses
as well as uncertainties from unknown higher order corrections. We find that
information on tan beta and M_A could be obtained from a cross section
measurement with a precision of 0.5 - 1 %. Alternatively, information could be
obtained on the gaugino mass parameters M_2 and mu if they are relatively
small, M_2, mu approximately 200 GeV.Comment: 13 pages, 3 figures. Discussion on experimental errors enlarged,
references added and updated. Version to appear in Phys. Rev.
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