3,639 research outputs found
Quantum loops in the Resonance Chiral Theory: improving the vector form factor
Quantum loops in the Resonance Chiral Theory are needed to improve the
implementation of non-perturbative QCD. Furthermore, the one-loop computations
can predict chiral low-energy couplings at next-to-leading order, a very
appealing task. We present a first calculation of the vector form factor of the
pion at subleading order in the 1/N_C expansion. From the analysis of the
result at large energies we justify the requirement of considering
short-distance constraints from form factors with resonances in the final
state. The long-distance limit of our results allows to get a next-to-leading
order estimate of \ell_6.Comment: Talk given at the International Workshop e+e- Collisions from phi to
J/psi, 27th February-2nd March (2006), Novosibirsk (Russia
One-loop Renormalization of Resonance Chiral Theory with Scalar and Pseudoscalar Resonances
The divergent part of the generating functional of the Resonance Chiral
Theory is evaluated up to one loop when one multiplet of scalar an pseudoscalar
resonances are included and interaction terms which couple up to two resonances
are considered. Hence we obtain the renormalization of the couplings of the
initial Lagrangian and, moreover, the complete list of operators that make this
theory finite, at this order.Comment: 4 pages, no figures. Talk given at the High-Energy Physics
International Conference on Quantum Chromodynamics, 2-9 July (2005),
Montpellier (France). To appear in the Proceeding
Enhanced Utilization of structural Damping of rotating Machines using impulsively shaped torsional Moments
The reduction of torsional vibrations of rotating machines is an important issue, as they may lead to a decrease of the performance, or in the worst case, to a damage of the machinery. In particular, self-excited vibrations have to be suppressed in any case due to their hazardous nature. In this contribution, a method is proposed, which allows utilizing the structural damping inherent to every rotating machine much more effectively by introducing impulsively shaped torsional moments, resulting in repeated modal transfers of vibration energy. Depending on the chosen impulsive strength, the energy transfers are accompanied by feeding external energy to, or extracting energy from the mechanical system. It is shown theoretically by approximating the impulses by Dirac-delta functions that an impulsive strength exists, where no energy crosses the system boundary, i.e. energy extracted from one mode is fed entirely to another mode of vibration. In the case of a conservative system, a repeated application of such impulses induces a periodic exchange of energy between lower and higher modes. Taking into account the structural damping reveals the advantages of transferring energy across modes. As higher modes possess higher damping ratios than lower ones, the structural damping of the rotating machine can be utilized much more effectively, which leads to a significant reduction of torsional vibrations. The underlying equations of motion of the impulsively excited system can be written as recursive difference equations with constant coefficients. Hence, the stability properties of the system can be investigated according to the Floquet theory. It is shown that the proposed concept is capable of suppressing self-excited vibrations. Stability charts are presented which allow to identify stable areas of operation. Finally, some numerical results of a test-rig are shown, underlining the effectivity of the proposed method
Renormalizable Sectors in Resonance Chiral Theory: S -> pi pi Decay Amplitude
We develop a resonance chiral theory without any a priori limitation on the
number of derivatives in the hadronic operators. Through an exhaustive analysis
of the resonance lagrangian and by means of field redefinitions, we find that
the number of independent operator contributing to the S -> pi pi decay
amplitude is finite: there is only one single-trace operator (the cd term) and
three multi-trace terms. The deep implication of this fact is that the
ultraviolet divergences that appear in this amplitude at the loop level can
only appear through these chiral invariant structures. Hence, a renormalization
of these couplings renders the amplitude finite.Comment: 4 page
Long distance contribution to decay and terms in CHPT
The long distance contribution to is
calculated using chiral perturbation theory. The leading contribution comes
from tree terms. The branching ratio of the long distance
contribution is found to be of order smaller than the short distance
contributions.Comment: 12 pages, 1 figure (available upon request
Role of Scalar Meson Resonances in $K_{L}^{0} \rightarrow \pi^{0} \gamma \gamma Decay
Corrections to decay induced by
scalar meson exchange are studied within chiral perturbation theory. In spite
of bad knowledge of scalar-mesons parameters, the calculated branching ratio
can be changed by a few percent.Comment: 18 pages of text, 2 figures (available upon request); preprint
IJS-TP-16-94 , TUM-T31-63-94
Improving the Hadronization of QCD currents in TAUOLA and PHOKHARA
We present our study of the hadronization structure of both vector and
axial-vector currents leading to decays of the tau into two kaons and a pion.
The cornerstones of our framework are the large-N_C limit of QCD, the chiral
structure exhibited at low energies and the proper asymptotic behaviour, ruled
by QCD, that is demanded to the associated form factors. The couplings of the
theory are mostly constrained by this procedure and upon the analysis of BaBar
data on e^+e^- -> KK pi we are able to predict the hadronic spectra.Comment: 4 pages, 1 figure. To appear in the Proceedings of QCD 08: 14th
International QCD Conference, 7-12th July 2008 Montpellier (France). To be
published by Elsevier in Nuclear Physics B (Proceedings Supplement
One loop corrections to quantum hadrodynamics with vector mesons
The renormalized elastic scattering amplitude to one loop is
calculated in the chiral limit in the model and in a Quantum
Hadrodynamic model (QHD-III) with vector mesons. It is argued that QHD-III
reduces to the linear model in the limit that the vector meson masses
become large. The pion decay constant is also calculated to 1-loop in the
model, and at tree level in QHD-III; it is shown that the coefficient
of the tree level term in the scattering amplitude equals . The
1-loop correction of in QHD-III violates strong isospin current
conservation. Thus,it is concluded that QHD-III can, at best, only describe the
strongly interacting nuclear sector.Comment: 6 page
Navigation-Assisted Posterior Open Reduction and Internal Fixation in a C-CLAMP Fashion for an Isolated C1 Fracture.
C1 fractures with an intact transverse ligament are usually treated conservatively. Patients who present with a progressive diastasis of bone fragments and a progressive articular subluxation mainly attributed to progressive lengthening of the transverse ligament (TAL) fibers can be treated with a C1 "C-clamp" fusion. A 75-year-old male who sustained a motor vehicle accident was neurologically intact. A computed tomography (CT) imaging demonstrated a Jefferson's type-C1 fracture with a slight lateral displacement of the C1 left lateral mass (LM) and a rotatory subluxation on the right. MRI showed an intact TAL and demonstrated an isolated rupture of the left alar ligament. Conservative treatment was chosen. Radiographic follow-up showed, at 3 months, progressive lateral mass displacement, most likely due to elongation of the TAL fibers; this was also associated with a persistent mechanical neck pain. For this reason, we performed a posterior reduction and internal fixation in a C-clamp fashion by placement of C1 lateral mass screws and posterior compression sparing the C1-2 joint. Using navigation, a 3.5-mm screw was inserted into the LM bilaterally. The screw heads were then connected with a rod and compression was applied before tightening. Postoperative CT scan demonstrated a satisfying reduction and further imaging will be made during the follow-up. The patient had a considerable relief of neck pain. Simple lateral mass fixation with C-clamp technique is a reasonable option in case of isolated C1 fractures in patients who have failed conservative management while preserving the range of motion (ROM) at the atlanto-axial joint. The link to the video can be found at: https://youtu.be/x8bsVwzCt_M
On the Corrections to Dashen's Theorem
The electromagnetic corrections to the masses of the pseudoscalar mesons
and are considered. We calculate in chiral perturbation theory the
contributions which arise from resonances within a photon loop at order . Within this approach we find rather moderate deviations to Dashen's
theorem.Comment: 14 pages, sligthly enlarged version; a numerical error is corrected
and the embedding of the figures is improved. The complete paper, including
figures, is also available via anonymous ftp at
ftp://www-ttp.physik.uni-karlsruhe.de/ , or via www at
http://www-ttp.physik.uni-karlsruhe.de/cgi-bin/preprints/; to be published in
Phys.Rev.
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