659 research outputs found
Strong and Radiative Meson Decays in a Generalized Nambu--Jona-Lasinio Model
We investigate strong and radiative meson decays in a generalized
Nambu--Jona-Lasinio model. The one loop order calculation provides a
satisfactory agreement with the data for the mesonic spectrum and for radiative
decays. Higher order effects for strong decays of and are
estimated to be large. We also discuss the role of the flavour mixing
determinantal interaction.Comment: 7 pages, LaTeX, 2 figs available upon request, CRN 92-4
Low-energy dynamics of the reaction
We calculate the one-quark-loop amplitude for the low energy
collision in the context of the Nambu and Jona-Lasinio
model with scalar and pseudoscalar four quark couplings to all orders in the
external momenta. We show that the NJL predictions for the
reaction are not far from the Born amplitude, which
is close to the data, and is compatible with the chiral perturbation theory
estimations. We determine the corrections given by the NJL model in leading
order of to the chiral loop amplitude for .
Numerical results for the cross sections and
for pion polarizabilities are given.Comment: 20 pages in LaTex, 3 figures in 1 Postscript fil
Spin structure of the nucleon at low energies
The spin structure of the nucleon is analyzed in the framework of a
Lorentz-invariant formulation of baryon chiral perturbation theory. The
structure functions of doubly virtual Compton scattering are calculated to
one-loop accuracy (fourth order in the chiral expansion). We discuss the
generalization of the Gerasimov-Drell-Hearn sum rule, the Burkhardt-Cottingham
sum rule and moments of these. We give predictions for the forward and the
longitudinal-transverse spin polarizabilities of the proton and the neutron at
zero and finite photon virtuality. A detailed comparison to results obtained in
heavy baryon chiral perturbation theory is also given.Comment: 29 pp, 14 fig
Role of CaO addition in the local order around Erbium in SiO2 –GeO2 –P2O5 fiber preforms
International audienceThe development of materials for optical signal processing represents a major issue in present technology. In this contribution we present a study on Er-doped fiber preforms where particular attention is devoted on how the addition of CaO in the glass modifies the local environment of the rare earth. The results from photoluminescence and Extended X-ray Absorption Fine Structure (EXAFS) are compared and a clear link between the width of the emission line at 1.5 µm and the amorphous/crystalline local structure around the Er3+ ion is evidenced
Profitability of diammonium phosphate use in bush and climbing bean-maize rotations in smallholder farms of Central Burundi
Article purchasedSoil fertility decline is a major constraint to bean (Phaseolus vulgaris L.) and maize (Zea mays) production in the Central Highlands of Burundi. Nutrient sources, specifically fertilizers, are paramount to increasing the production in the regions. Hence, improving fertilizer use efficiency is considered as a key factor towards sustainable intensification. The use of grain legumes with low harvest indices, such as climbing beans, are assumed to improve soil fertility and fertilizer use efficiency. This study compares the rotational effects of bush and climbing bean varieties on maize and evaluates the profitability of diammonium phosphate (DAP, 18–46-0) fertilizer in the bean-maize rotations in 59 smallholder farms of Mutaho district, Gitega Province in Central Burundi. The application of DAP fertilizer significantly increased the grain yields by 14% and 21% for bush and climbing beans, respectively (P 2 −1) in a climbing bean-maize rotation while 45% of the farmers in a bush bean-maize rotation. Regression tree analysis showed that targeting fertilizer use to soils with higher C and clay content, and ensuring timely planting are the predominant factors to ensure fertilizer response and profitable returns. This study confirms the need for integrated soil fertility management (ISFM), and that a combination of judicious fertilizer use, an improved grain legume (climbing bean) and adjustment to local conditions (targeting to responsive soils) maximizes economic returns of legume-cereal rotation systems
Finite-volume meson propagators in quenched chiral perturbation theory
We compute meson propagators in finite-volume quenched chiral perturbation
theory.Comment: 3 pages, Lattice2001(chiral fermions
On the Renormalization of a Bosonized Version of the Chiral Fermion-Meson Model at Finite Temperature
Feynman's functional formulation of statistical mechanics is used to study
the renormalizability of the well known Linear Chiral Sigma Model in the
presence of fermionic fields at finite temperature in an alternative way. It is
shown that the renormalization conditions coincide with those of the zero
temperature model.Comment: 12 pages, no figures, LaTex, reference [17] is updated, to appear in
Phys. Lett.
Weak Liouville-Arnold Theorems & Their Implications
This paper studies the existence of invariant smooth Lagrangian graphs for
Tonelli Hamiltonian systems with symmetries. In particular, we consider Tonelli
Hamiltonians with n independent but not necessarily involutive constants of
motion and obtain two theorems reminiscent of the Liouville-Arnold theorem.
Moreover, we also obtain results on the structure of the configuration spaces
of such systems that are reminiscent of results on the configuration space of
completely integrable Tonelli Hamiltonians.Comment: 24 pages, 1 figure; v2 corrects typo in online abstract; v3 includes
new title (was: A Weak Liouville-Arnold Theorem), re-arrangement of
introduction, re-numbering of main theorems; v4 updates the authors' email
and physical addresses, clarifies notation in section 4. Final versio
A comparative analysis of currency volatility among BRICS countries
In recent years, exchange rates of the BRICS countries have all experienced periods of high volatility. Thus far, no study has simultaneously compared the volatility of the BRICS currencies and analyzed the dependence and causal structure of relative volatility of these peer currencies. We addressed this issue by using monthly data from January 1995 to January 2017. We find that:(i) Brazil, India and China are more competitive than South Africa, on average, while South Africa, in turn, is only more competitive than Russia;(ii) the rand has been more volatile than the Brazilian real and the Russian ruble, but less volatile than the Chinese renminbi and the Indian rupee; (iii) there are inter-currency volatility correlations among the real, renminbi, ruble, and rand;(iv) the renminbi return volatility causes return volatility in the real, ruble, and rand.http://www.tandfonline.com/loi/wjab202020-09-27hj2020Economic
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