共查询到20条相似文献,搜索用时 0 毫秒
1.
Gauhar Abbas B. Ananthanarayan S. Ramanan 《The European Physical Journal A - Hadrons and Nuclei》2009,41(1):93-100
We study the constraints arising on the expansion parameters c and d of the pion electromagnetic form factor from the inclusion of pure spacelike data and the phase of timelike data along with
one spacelike datum, using as input the first derivative of the QCD polarization amplitude (- Q
2) . These constraints when combined with other analyses, provide a valuable check on a determination of c due to Guo et al. and on our previous work where pionic contribution to the (g - 2) of the muon was used as the input. This work further illustrates the power of analyticity techniques in form factor
analysis. 相似文献
2.
We perform a theoretical study based on dispersion relations of the reaction γγ → π
0
π
0 emphasizing the low-energy region. We discuss how the ƒ
0(980) signal emerges in γγ → ππ within the dispersive approach and how this fixes to a large extent the phase of the isoscalar S-wave γγ → ππ amplitude above the threshold. This allows us to make sharper predictions for the cross-section at lower energies and our results could then
be used to distinguish between different ππ isoscalar S-wave parameterizations with the advent of new precise data on ππ → π
0
π
0. We compare our dispersive approach with an updated calculation employing the unitary chiral perturbation theory (U
gC
PT). We also pay special attention to the role played by the σ-resonance in γγ → ππ and calculate its coupling and width to γγ, for which we obtain Γ(σ → γγ) = (1.68 ± 0.15) keV. 相似文献
3.
4.
5.
K. Azizi R. Khosravi V. Bashiry 《The European Physical Journal C - Particles and Fields》2008,56(3):357-370
Taking into account the gluon correction contributions to the correlation function, the form factors relevant to the rare
decays are calculated in the framework of the three-point QCD sum rules, where X stands for axial vector particle, AV(D
s1), and vector particles, V(D
*,D
s
*). The total decay width as well as the branching ratio of these decays are evaluated using the q
2 dependent expressions of the form factors. A comparison of our results with the predictions of the relativistic constituent
quark model is presented. 相似文献
6.
V. V. Rubish V. Yu. Lazur O. K. Reity S. Chalupka M. Salak 《Czechoslovak Journal of Physics》2004,54(9):897-919
The WKB approximation is developed for the Dirac equation with the spherically symmetrical vector and scalar potentials. The
relativistic wavefunctions are constructed, new quantization rule containing the spin-orbital interaction is obtained. For
spherically symmetrical model of the Stark effect the quasi-classical spectrum of relativistic hydrogen-like atom is calculated.
Application of the WKB method to the mass spectrum of the hydrogen-like quark systems was done. 相似文献
7.
The decays η,
→ π+π-
l
+
l
- (with l = e,μ are investigated within a chiral unitary approach which combines the chiral effective Lagrangian with a coupled-channels
Bethe-Salpeter equation. Predictions for the decay widths and spectra are given. 相似文献
8.
Gauhar Abbas B. Ananthanarayan I. Caprini I. Sentitemsu Imsong S. Ramanan 《The European Physical Journal A - Hadrons and Nuclei》2010,44(2):175-179
We investigate the scalar K
p \pi form factor at low energies by the method of unitarity bounds adapted so as to include information on the phase and modulus
along the elastic region of the unitarity cut. Using at input the values of the form factor at t = 0 and the Callan-Treiman point, we obtain stringent constraints on the slope and curvature parameters of the Taylor expansion
at the origin. Also, we predict a quite narrow range for the higher-order ChPT corrections at the second Callan-Treiman point. 相似文献
9.
D. Ebert R. N. Faustov V. O. Galkin 《The European Physical Journal C - Particles and Fields》2009,60(2):273-278
Masses of the ground-state light tetraquarks are dynamically calculated in the framework of the relativistic diquark–antidiquark
picture. The internal structure of the diquark is taken into account by calculating the form factor of the diquark–gluon interaction
in terms of the overlap integral of the diquark wave functions. It is found that scalar mesons with masses below 1 GeV, f
0(600) (σ), K
0*(800) (κ), f
0(980) and a
0(980), agree well with the light-tetraquark interpretation. 相似文献
10.
F.?-K.?Guo C.?Hanhart U.?-G.?Mei?ner 《The European Physical Journal A - Hadrons and Nuclei》2009,40(2):171-179
We calculate the S -wave scattering lengths for charmed mesons scattering off Goldstone bosons and explore their quark mass dependence using
the chiral perturbation theory up to next-to-leading order as well as a unitarized version of it. The quark mass dependence
of all scattering lengths determined in a recent lattice calculation can be reproduced by the unitarized version. We also
discuss signals of possible bound states in these observables. 相似文献
11.
P. C. Bruns U.-G. Meißner 《The European Physical Journal C - Particles and Fields》2008,58(3):407-422
We extend the method of infrared regularization to spin-1 fields coupled to baryons. As an application, we discuss the axial
form factor of the nucleon. 相似文献
12.
A new procedure is devised to evaluate the proton form-factor at the ¯pp threshold from experimental data on ¯ppe
+
e
– annihilation at rest. Comparison of the ¯ppe
+
e
– and¯pp
+– processes reveals that annihilation ranges for various channels are ranked in line with quark dynamics.This work has been funded in part by the German Federal Minister for Research and Technology (BMFT) under the contract number 06HD756 相似文献
13.
R. Alkofer H. Reinhardt J. Schlienz H. Weigel 《Zeitschrift für Physik A Hadrons and Nuclei》1996,354(1):181-195
The role of chiral transformations in effective theories modeling Quantum Chromo Dynamics is reviewed. In the context of the Nambu-Jona-Lasinio model the hidden gauge and massive Yang-Mills approaches to vector mesons are linked by a special chiral transformation which removes the chiral field from the scalar-pseudoscalar sector. The chirally rotated axial vector meson field (à μ ) transforms homogeneously under flavor rotations and may thus be dropped without violating chiral symmetry. The fermion determinant for static meson field configurations is computed by summing the discretized eigenvalues of the Dirac Hamiltonian. It is discussed how the local chiral transformation loses its unitary character in a finite model space. This technical issue proves to be crucial for the construction of the soliton within the Nambu-Jona-Lasinio model when the chirally rotated axial vector field is neglected. In the background of this soliton the valence quark is strongly bound, and its eigenenergy turns out to be negative. This important feature, which usually is generated by non-vanishing axial vector profiles, is thus maintained by the simplificationà μ = 0. 相似文献
14.
D. V. Shirkov 《Physics of Particles and Nuclei Letters》2008,5(6):489-493
In quantum theory, physical amplitudes are usually presented in the form of a Feynman perturbation series in powers of coupling
constant α. However, it is known that these amplitudes are not regular functions at α = 0.
For QCD, we propose new sets of expansion parameters w
k
(α
s
) that reflect singularity at α
s
= 0 and should be used instead of powers α
s
k
. Their explicit form is motivated by the so-called Analytic Perturbation Theory. These parameters reveal saturation in a
strong coupling case at the level α
s
eff (α
s
1) = w
1(α
s
1) ∼ 0.5. They can be used for the quantitative analysis of divers low-energy amplitudes.
We argue that this new picture with non-power sets of perturbation expansion parameters, as well as the saturation feature,
is of a rather general nature.
The text was submitted by the author in English.
A preliminary version with the main results was published in [1]. 相似文献
15.
Charged perfect fluid with vanishing Lorentz force and massless scalar field is studied for the case of stationary cylindrically symmetric spacetime. The scalar field can depend both on radial and longitudinal coordinates. Solutions are found and classified according to scalar field gradient and magnetic field relationship. Their physical and geometrical properties are examined and discussion of particular cases, directly generalizing Gödel-type spacetimes, is presented. 相似文献
16.
Zhi-Gang Luo Xiao-Lin Chen Xiang Liu Shi-Lin Zhu 《The European Physical Journal C - Particles and Fields》2009,60(3):403-411
Stimulated by recent observations of the excited bottom–strange mesons B
s1 and B
s2*, we calculate the semileptonic decays
, which is relevant for the exploration of the potential of searching these semileptonic decays in experiment. 相似文献
17.
The decays of light vector mesons into three pseudoscalar mesons are calculated to leading order in the recently proposed
counting scheme that is based on the hadrogenesis conjecture. Fully differential as well as integrated decay widths are presented.
Since the required parameters have been fixed by other processes, the considered three-body decays are predictions of the
presented approach. The decay width of the omega meson into three pions agrees very well with the experiment. The partial
decay widths of the K* into its three K
channels are predicted. 相似文献
18.
The
andO (
S
2
) corrections to the leading term of the perturbative QCD calculation of the pion electromagnetic form factor are examined numerically. Both sets of terms provide significant corrections for values ofQ
2 between 1 and 15 GeV2/c2.Parts of this work were done while one of us (JP) was a visitor at the national INT, the University of Maryland and TRIUMF. He is grateful to those institutions for their hospitality. We have benefitted from discussions with A. Mueller and G. Sterman. This work is supported in part by the U.S. Department of Energy. 相似文献
19.
The intensive studies of equilibration processes in heavy ion reactions have produced a need for information on nuclear level densities at high energies. In a recent paper, it was concluded that standard Fermi gas formulas will be incorrect by exponential factors at energies above 100 MeV. Exact calculations of the nuclear level density in bases as large as 1038 have been made and are compared with Fermi gas formulas. Two possible alternative forms are considered. Both forms produce much better agreement at high energies than does the Fermi gas model. All calculations reported are for non-interacting Fermions, but the effects expected from the two-body interaction are briefly examined. These considerations have consequences not only in heavy ion physics but also in astrophysics. 相似文献
20.
?nan? ?ahin 《The European Physical Journal C - Particles and Fields》2009,60(3):431-439
We investigate the potential of γ
γ collisions to probe scalar unparticle couplings via top–antitop quark pair production. We find 95% confidence level limits
on the unparticle couplings with an integrated luminosity of 500 fb−1 and an energy of
TeV. We investigate the effect of the top quark spin polarization on the unparticle couplings. It is shown that spin polarization
of the top quark leads to a significant improvement in the sensitivity limits. 相似文献