1,086 research outputs found
Hadronic unquenching effects in the quark propagator
We investigate hadronic unquenching effects in light quarks and mesons.
Within the non-perturbative continuum framework of Schwinger-Dyson and
Bethe-Salpeter equations we quantify the strength of the back reaction of the
pion onto the quark-gluon interaction. To this end we add a Yang-Mills part of
the interaction such that unquenched lattice results for various current quark
masses are reproduced. We find considerable effects in the quark mass function
at low momenta as well as for the chiral condensate. The quark wave function is
less affected. The Gell--Mann-Oakes-Renner relation is valid to good accuracy
up to pion masses of 400-500 MeV. As a byproduct of our investigation we verify
the Coleman theorem, that chiral symmetry cannot be broken spontaneously when
QCD is reduced to 1+1 dimensions.Comment: 27 pages, 15 figures, minor corrections and clarifications; version
to appear in PR
Little Higgs Models and Precision Electroweak Data
We study the low energy limit of Little Higgs models. The method consists in
eliminating the heavy fields using their classical equations of motion in the
infinite mass limit. After the elimination of the heavy degrees of freedom we
can directly read off deviations from the precision electroweak data. We also
examine the effects on the low energy precision experiments.Comment: Misprint in eps3 for the custodial model corrected and additional
discussion of the triplet higg
Two regularizations - two different models of Nambu-Jona-Lasinio
Two variants of the Nambu--Jona-Lasinio model -- the model with 4-dimensional
cutoff and the model with dimensionally-analytical regularization -- are
systematically compared. It is shown that they are, in essence, two different
models of light-quark interaction. In the mean-field approximation the
distinction becomes apparent in a behavior of scalar amplitude near the
threshold. For 4-dimensional cutoff the pole term can be extracted, which
corresponds to sigma-meson. For dimensionally-analytical regularization the
singularity of the scalar amplitude is not pole, and this singularity is quite
disappeared at some value of the regularization parameter.
Still more essential distinction of these models exists in the
next-to-leading order of mean-field expansion. The calculations of meson
contributions in the quark chiral condensate and in the dynamical quark mass
demonstrate, that these contributions though their relatively smallness can
destabilize the Nambu--Jona-Lasinio model with 4-dimensional cutoff. On the
contrary, the Nambu--Jona-Lasinio model with dimensionally-analytical
regularization is stabilized with the next-to-leading order, i.e. the value of
the regularization parameter shifts to the stability region, where these
contributions decrease.Comment: 14 pages; Journal version; parameter fixing procedure is modifie
Analysis of climate change scenarios based on modelling of the seasonal dynamics of a Danubian copepod species
Climate change is one of the most crucial ecological problems of our age with great influence.
Seasonal dynamics of aquatic communities are — among others — regulated by the climate, especially
by temperature. In this case study we attempted the simulation modelling of the seasonal dynamics of a
copepod species, Cyclops vicinus, which ranks among the zooplankton community, based on a
quantitative database containing ten years of data from the Danube’s Göd area. We set up a simulation
model predicting the abundance of Cyclops vicinus by considering only temperature as it affects the
abundance of population. The model was adapted to eight years of daily temperature data observed
between 1981 and 1994 and was tested successfully with the additional data of two further years. The
model was run with the data series of climate change scenarios specified for the period around 2070-
2100. On the other hand we looked for the geographically analogous areas with the Göd region which are
mostly similar to the future climate of the Göd area. By means of the above-mentioned points we can get
a view how the climate of the region will change by the end of the 21st century, and the way the seasonal
dynamics of a chosen planktonic crustacean species may follow this change. According to our results the
area of Göd will be similar to the northern region of Greece. The maximum abundance of the examined
species occurs a month to one and a half months earlier, moreover larger variances are expected between
years in respect of the abundance. The deviations are expected in the direction of smaller or significantly
larger abundance not observed earlier
Meson loop effects in the NJL model at zero and non-zero temperature
We compare two different possibilities to include meson-loop corrections in
the Nambu-Jona-Lasinio model: a strict 1/N_c-expansion in next-to-leading order
and a non-perturbative scheme corresponding to a one-meson-loop approximation
to the effective action. Both schemes are consistent with chiral symmetry, in
particular with the Goldstone theorem and the Gell-Mann-Oakes-Renner relation.
The numerical part at zero temperature focuses on the pion and the rho-meson
sector. For the latter the meson-loop-corrections are crucial in order to
include the dominant rho -> pipi-decay channel, while the standard Hartree +
RPA approximation only contains unphysical qqbar-decay channels. We find that
m_\pi, f_\pi, and quantities related to the rho-meson self-energy can
be described reasonably with one parameter set in the 1/N_c-expansion scheme,
whereas we did not succeed to obtain such a fit in the non-perturbative scheme.
We also investigate the temperature dependence of the quark condensate. Here we
find consistency with chiral perturbation theory to lowest order. Similarities
and differences of both schemes are discussed.Comment: 51 pages, 18 figures, to be published in Physics of Atomic Nuclei,
the volume dedicated to the 90th birthday of A.B. Migdal, error in Eq. 4.22
correcte
Malignancy risk analysis in patients with inadequate fine needle aspiration cytology (FNAC) of the thyroid
Background
Thyroid fine needle aspiration cytology (FNAC) is the standard diagnostic modality for thyroid nodules. However, it has limitations among which is the incidence of non-diagnostic results (Thy1). Management of cases with repeatedly non-diagnostic FNAC ranges from simple observation to surgical intervention. We aim to evaluate the incidence of malignancy in non-diagnostic FNAC, and the success rate of repeated FNAC. We also aim to evaluate risk factors for malignancy in patients with non-diagnostic FNAC.
Materials and Methods
Retrospective analyses of consecutive cases with thyroid non diagnostic FNAC results were included.
Results
Out of total 1657 thyroid FNAC done during the study period, there were 264 (15.9%) non-diagnostic FNAC on the first attempt. On repeating those, the rate of a non-diagnostic result on second FNAC was 61.8% and on third FNAC was 47.2%. The overall malignancy rate in Thy1 FNAC was 4.5% (42% papillary, 42% follicular and 8% anaplastic), and the yield of malignancy decreased considerably with successive non-diagnostic FNAC. Ultrasound guidance by an experienced head neck radiologist produced the lowest non-diagnostic rate (38%) on repetition compared to US guidance by a generalist radiologist (65%) and by non US guidance (90%).
Conclusions
There is a low risk of malignancy in patients with a non-diagnostic FNAC result, commensurate to the risk of any nodule. The yield of malignancy decreased considerably with successive non-diagnostic FNAC
Dispersive representation and shape of the Kl3 form factors: robustness
An accurate low-energy dispersive parametrization of the scalar Kpi form
factor was constructed some time ago in terms of a single parameter guided by
the Callan-Treiman low-energy theorem. A similar twice subtracted dispersive
parametrization for the vector Kpi form factor will be investigated here. The
robustness of the parametrization of these two form factors will be studied in
great detail. In particular the cut-off dependence, the isospin breaking
effects and the possible, though not highly probable, presence of zeros in the
form factors will be discussed. Interesting constraints in the latter case will
be obtained from the soft-kaon analog of the Callan-Treiman theorem and a
comparison with the recent tau --> K pi nu_tau data.Comment: 24 pages, 11 figure
- …