共查询到20条相似文献,搜索用时 31 毫秒
1.
In the perturbative QCD approach single and double inclusive cross-sections for gluon production off the nucleus are studied by the relevant reggeized gluon diagrams. Various terms corresponding to emission of gluons from the triple pomeron vertex are found. Among them the term derived by Kovchegov and Tuchin emerges as a result of the transition from the diffractive to effective high-energy vertex. However it does not exhaust all the vertex contributions to the inclusive cross-section. In the double inclusive cross-section a contribution violating the naive AGK rules is found in which one gluon is emitted from the vertex and the other from one of the two pomerons below the vertex. But then this contribution is subdominant at high energies and taking it into account seems to be questionable.Received: 6 March 2005, Revised: 5 May 2005, Published online: 8 June 2005 相似文献
2.
The study of charmonium dissociation in heavy ion collisions is generally performed in the framework of effective Lagrangians with meson exchange. Some studies are also developed with the intention of calculate form factors and coupling constants related with charmed and light mesons. These quantities are important in the evaluation of charmonium cross sections. In this Letter we present a calculation of the ωDD vertex that is a possible interaction vertex in some meson-exchange models spread in the literature. We used the standard method of QCD sum rules in order to obtain the vertex form factor as a function of the transferred momentum. Our results are compatible with the value of this vertex form factor (at zero momentum transfer) obtained in the vector-meson dominance model. 相似文献
3.
S. Descotes-Genon B. Moussallam 《The European Physical Journal C - Particles and Fields》2005,42(4):403-417
We focus on the chiral Lagrangian couplings describing radiative corrections to weak semi-leptonic decays and relate them to the decay amplitude of a lepton, computed by Braaten and Li at one loop in the standard model. For this purpose, we follow a two-step procedure. A first matching, from the standard model to Fermi theory, yields a relevant set of counterterms. The latter are related to chiral couplings thanks to a second matching, from Fermi theory to the chiral Lagrangian, which is performed using the spurion method. We show that the chiral couplings of physical relevance obey integral representations in a closed form, expressed in terms of QCD chiral correlators and vertex functions. We deduce exact relations among the couplings, as well as numerical estimates which go beyond the usual
approximation.Received: 16 May 2005, Published online: 19 July 2005 相似文献
4.
A.Nyffeler 《中国物理C(英文版)》2010,34(6):705-711
We review recent developments concerning the hadronic light-by-light scattering contribution to the anomalous magnetic moment of the muon.We first discuss why fully off-shell hadronic form factors should be used for the evaluation of this contribution to the g-2.We then reevaluate the numerically dominant pion-exchange contribution in the framework of large-NC QCD,using an off-shell pion-photon-photon form factor which fulfills all QCD short-distance constraints,in particular,a new short-distance constraint on the off-shell form factor at the external vertex in g-2,which relates the form factor to the quark condensate magnetic susceptibility in QCD.Combined with available evaluations of the other contributions to hadronic light-by-light scattering this leads to the new result aLμb yL;had=(116±40)×10-11,with a conservative error estimate in view of the many still unsolved problems.Some potential ways for further improvements are briefly discussed as well.For the electron we obtain the new estimate aLe byL;had=(3.9±1.3)×10-14. 相似文献
5.
We calculate the form factors and the coupling constant in the Ds0DK vertex in the framework of QCD sum rules. We evaluate the three point correlation functions of the vertex considering both D and K mesons off-shell. The form factors obtained are very different but give the same coupling constant. 相似文献
6.
The phase structure of zero temperature twisted mass lattice QCD is investigated. We find strong metastabilities in the plaquette observable in correspondence of which the untwisted quark mass assumes positive or negative values. We provide interpretations of this phenomenon in terms of chiral symmetry breaking and the effective potential model of Sharpe and Singleton.Received: 24 August 2004, Revised: 29 October 2004, Published online: 25 January 2005 相似文献
7.
We analyze the ρ-A 1-π system within the context of vertex light-cone sum rules, which are believed to be rigorously satisfied in QCD. It is pointed out that these sum rules provide very strong constraints on the hadronic spectrum and with additional assumptions lead to new predictions, which go significantly beyond those obtained from current algebra in the past. In particular, we report some new results about the ρ-A 1-π couplings and the various transition form factors in τ-semi-leptonic decays. 相似文献
8.
J. Bartels D. Colferai G.P. Vacca 《The European Physical Journal C - Particles and Fields》2003,29(2):235-249
In this paper we complete our calculation of the NLO jet vertex which is part of the cross section formulae for the production
of Mueller Navelet jets at hadron hadron colliders and of forward jets in deep inelastic electron proton scattering.
Received: 2 September 2002 / Revised version: 16 January 2003 / Published online: 2 June 2003
RID="a"
ID="a" Supported by the TMR Network "QCD and Deep Structure of Elementary Particles"
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ID="b" Supported by the Alexander von Humboldt Stiftung 相似文献
9.
The three-loop form factors in massless QCD can be expressed as a linear combination of master integrals. Besides a number of master integrals which factorise into products of one-loop and two-loop integrals, one finds 16 genuine three-loop integrals. Of these, six have the form of a bubble insertion inside a one-loop or two-loop vertex integral. We compute all master integrals with these insertion topologies. 相似文献
10.
Cai-Dian Lü Yue-long Shen Jin Zhu 《The European Physical Journal C - Particles and Fields》2005,41(3):311-317
The rare decay
can occur only via the penguin annihilation topology in the standard model. We calculate this channel in the perturbative QCD approach. The predicted branching ratio is very small: around 10-8. We also give the polarization fractions, which show that the transverse polarization contribution is comparable to the longitudinal one, due to a big transverse contribution from factorizable diagrams. The small branching ratio in SM makes it sensitive to any new physics contributions.Received: 29 January 2005, Published online: 28 April 2005 相似文献
11.
The H Collaboration 《The European Physical Journal C - Particles and Fields》2005,41(3):273-286
Measurements are reported of the production of dijet events with a leading neutron in ep interactions at HERA. Differential cross sections for photoproduction and deep inelastic scattering are presented as a function of several kinematic variables. Leading order QCD simulation programs are compared with the measurements. Models in which the real or virtual photon interacts with a parton of an exchanged pion are able to describe the data. Next-to-leading order perturbative QCD calculations based on pion exchange are found to be in good agreement with the measured cross sections. The fraction of leading neutron dijet events with respect to all dijet events is also determined. The dijet events with a leading neutron have a lower fraction of resolved photon processes than do the inclusive dijet data.Received: 31 January 2005, Revised: 7 March 2005, Published online: 28 April 2005 相似文献
12.
HE Han-Xin 《理论物理通讯》2009,52(2):292-294
The transverse symmetry transformations associated with the normal symmetry transformations are proposed to build the transverse constraints on the basic vertices in gauge theories. I show that, while the BRST symmetry in non-Abelian gauge theory QCD (Quantum Chromodynamics) leads to the Slavnov-Taylor identity for the quark-gluon vertex which constrains the longitudinal part of thevertex, the transverse symmetry transformation associated with the BRST symmetry enables to derive the transverse Slavnov-Taylor identity for the quark-gluon vertex, which constrains the transverse part of the quark-gluon vertex from the gauge symmetry of QCD. 相似文献
13.
We discuss the energy dependence of the gap survival probability which follows from the rational form of the amplitude unitarization. In contrast to the eikonal form of unitarization which leads to a decreasing energy dependence of the gap survival probability, we predict a non-monotonous form for this dependence.Received: 8 April 2004, Revised: 31 October 2004, Published online: 25 January 2005 相似文献
14.
Di-gluon fusion mechanism might account for the large branching ratios of B→Kη′. But because we know little about the effective η′ɡɡ vertex, there are large uncertainties in perturbative QCD estimations. In this paper, we try several kinds of η′ɡɡ form factors and compare the numerical results with the experiment. We find that, though we know little about η′ɡɡ form factor, if di-gluon fusion mechanism is important in B→Kη′, the branching ratios of the decays B→K*η′ would be around 10-5 which can be tested by future experiments. 相似文献
15.
J. Bartels M.G. Ryskin G.P. Vacca 《The European Physical Journal C - Particles and Fields》2003,27(1):101-113
We estimate the size of the triple-pomeron vertex in perturbative QCD and compare with the phenomenological value extracted
from Regge fits to the experimental data. For simplicity, the results of the QCD analysis are taken in the large-Nc limit. We find that the perturbative triple-pomeron coupling is of the same order of magnitude as the observed one. We also
estimate the size of the pomeron self-energy and its contribution to the renormalization of the pomeron intercept. The effect
is very small, in agreement with previous non-perturbative estimates.
Received: 9 October 2002 / Published online: 20 December 2002 相似文献
16.
In this Letter we show that the claim made in [V. Gogohia, Phys. Lett. B 611 (2005) 129] that the ladder approximation to QCD is internally inconsistent is incorrect. The incorrect conclusion in [V. Gogohia, Phys. Lett. B 611 (2005) 129] is based on the incorrect use of a QED-type Ward–Takahashi relation, which does not hold in the ladder approximation to QCD. We give a proof for this fact. 相似文献
17.
M.A. Braun 《The European Physical Journal C - Particles and Fields》2006,48(2):501-510
Single and double inclusive cross-sections for gluon jet production from within the triple pomeron vertex are studied in the reggeized gluon technique in the QCD with Nc→∞. It is shown that to satisfy the AGK rules the vertex has to be fully symmetric in all four reggeized gluons which form the two final pomerons. The single inclusive cross-sections are found for different cuttings of the triple pomeron vertex. They sum to the expression obtained by Kovchegov and Tuchin in the color dipole picture. The found double inclusive cross-sections satisfy the AGK rules. 相似文献
18.
We investigate spin-dependent parton distributions in the polarized virtual photon target in perturbative QCD up to the next-to-leading
order (NLO). In the case , where is the mass squared of the probe (target) photon, the parton distributions can be predicted completely up to NLO, but they
are factorization-scheme dependent. We analyze the parton distributions in six different factorization schemes and discuss
their scheme dependence. We study, in particular, the QCD and QED axial anomaly effects on the first moments of the parton
distributions to see the interplay between the axial anomalies and factorization schemes. We also show that the factorization-scheme
dependence is characterized by the large-x behaviors of the quark distributions in the virtual photon. The gluon distribution is predicted to be the same up to NLO
among the six factorization schemes examined. In particular, the first moment of the gluon distribution is found to be factorization-scheme
independent up to NLO.
Received: 24 January 2001 / Published online: 18 May 2001 相似文献
19.
We analyze the higher-twist effects and the SU(3)-flavor symmetry breaking in the correlation functions used to calculate form factors of pseudoscalar mesons in the QCD
light-cone sum rule approach. It is shown that the Ward identities for these correlation functions yield relations between
twist-4 two- and three-particle distribution amplitudes. In addition to the relations already obtained from the QCD equations
of motions, we have found a new one. With the help of these relations, the twist-4 contribution to the light-cone sum rule
for the pion electromagnetic form factor is reduced to a very simple form. Simultaneously, we correct a sign error in an earlier
calculation. The updated light-cone sum rule prediction for the pion form factor at intermediate momentum transfers is compared
with the recent Jefferson Lab data. Furthermore, from the correlation functions with strange-quark currents the kaon electromagnetic
form factor and the weak transition form factors are predicted with accuracy.
Received: 30 June 2002 / Published online: 7 October 2002
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20.
L. Driesen J. Fromm J. Kuhrs M. Stingl 《The European Physical Journal A - Hadrons and Nuclei》1999,4(4):381-400
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 Λ, we establish the self-consistency equations of the extended
Feynman rules (Λ-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.
Received: 1 September 1998 / Revised version: 1 December 1998 相似文献