首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
We discuss a scalar meson coupled strongly to gluons. Radiative decays of the J/ψ are taken as a source of gluons so that our aim is to calculate Γ(J/ψσγ), where σ is the presumed scalar gluonium. We use QCD sum rules to find both 〈0|αsGμνaGμνa|σ〉 (where Gμνa is the gluon field strength tensor) and Γ(J/ψσγ) in terms of 〈0|αsGμνaGμνa|σ〉. The final prediction for the width is expected to be valid within a factor of two and gives Γ(J/ψ→σγ→two pions in S-wave + γ) ? 25 eV for mσ = 700 MeV. Non-perturbative QCD naturally explains the observed asymmetry between scalar and pseudoscalar states in the radiative decays of the J/ψ. Some general remarks on gluonium in QCD are made.  相似文献   

2.
Using QCD sum rules for the polarization operator ∏J(Q2) induced by all possible currents with JPC=0??, 1??, 0++, 1++ and 2++ we calculate the S- and P-states of charmonium. Power corrections due to the gluon condensate operator GαμνGαμν are included and shown to be very important. All known lowest lying charmonium states are reproduced extremely well and a firm prediction is made for the 1P1 state.  相似文献   

3.
An effective action for QCD at one-loop order, which is real, manifestly Lorentz and gauge invariant and which depends on an infinite family of gauge invariants (tr(F μν F μν), tr(F μν F μν F F ),...), is obtained. Moreover, anAnsatz for a vacuum configuration is made, whose corresponding vacuum energy density is lower than the one for the SavvidyAnsatz. Both the cases of pure QCD and of QCD with massless fermions are considered.  相似文献   

4.
We present some techniques for elucidating hadronic structure via lattice Monte Carlo calculations. Applying these techniques, we measure the fluctuations of colour magnetic and electric fields as well as the topological charge density inside and outside the lowest lying 0+ and 2+ glueballs in the SU(2) non-abelian lattice gauge theory. This gives us a picture of the glueball structure. We also obtain, as a by-product, an estimate of the gluon condensate (αs/π)〈π|FμνaFμνa|Ω〈 and an estimate of the 0? glueball mass which agrees with our previous estimates.  相似文献   

5.
《Nuclear Physics B》1986,266(2):265-273
We calculate the multiplicity of heavy quark pairs in gluon jets in lowest order QCD, along with the non-perturbative correction related to the gluon condensate 〈(α/π)F2〉. The value of the non-perturbative correction is
where M is the mass of the heavy quark, N is the number of colors, and CF and CA are the values of the Casimir operators in the fundamental and adjoint representation respectively. α(M) is the running coupling constant at the scale of the heavy quark, and 〈F2〉 is the gluon condensate, usually determined to be 〈α/πF2〉 ∼ 0.012 GeV4. The non-perturbative correction is extremely small.  相似文献   

6.
We construct a potential for qurkonium systems using as the basic ingredients the gluon condensate, i.e., 〈0∥GμνaGμνa∥0〉 ≠ 0 to incorporate nonperturbative effects and using quark screening. The potential is able to account satisfactorily for the ss, cc and bb bound states with a flavor independent, essentially constant value for the effective coupling constant (αS ≈ 0.45). We also investigate heavier quark systems with the constant αS and find that for quark mass ? 20 GeV the potential is essentially coulombic.  相似文献   

7.
We consider the influence of the gluon condensate in QCD on the energy levels of quarkonia, taking into account the x-dependence of 〈ω|:Gμva(x) Gaμv(0):|ω〉. The modification compared to earlier approaches which approxim ated the above vacuum expectation value by a constant is quite sizeable; for the b?b system we find that the effect can be essentially described in terms of a local potential.  相似文献   

8.
M. Glück  E. Reya 《Nuclear Physics B》1979,156(3):456-464
It is demonstrated that recent measurements of ∫10F2(x, Q2)dx eliminate already all strong interaction field theories except QCD. A detailed study of scaling violations of F2(x, Q2) in QCD shows their insensitivity to the gluon content of the hadron at presently measured values of Q2.  相似文献   

9.
Based on the dilute gas approximation (DGA) with repulsive and dipole interactions we discuss the N dependence of the vacuum energy density, 〈αSFμνaFμνa〉 and of the topological charge correlation function at the crossover point of the instanton driven β function with the strong coupling one.  相似文献   

10.
We analyze a model of cold axion dark matter weakly coupled with a dark gluon condensate,reproducing dark energy.We first review how to recover the dark energy behavior using the functional renormalization group approach,and ground our study in the properties of the effective Lagrangian,to be determined non-perturbatively.Then,within the context of G_(SM)×SU(2)_D×U(1)_(P Q),we consider Yang-Mills condensate(YMC)interactions with QCD axions.We predict a transfer of dark energy density into dark matter density,that can be tested in the next generation of experiments dedicated to dark energy measurements.We obtain new bounds on the interactions between the Yang-Mills condensate and axion dark matter from Planck data:the new physics interaction scale related to the axion/gluon condensate mixing is constrained to be higher than the 10~6GeV energy scale.  相似文献   

11.
For field theories that include the abelian gauge field Aμν? the field equations allow an arbitrary integration constant, which does not appear in the lagrangian but which does affect the physics. We present two applications: (i) the θ parameter of effective lagrangians for chiral symmetry breaking in QCD, and (ii) the cosmological constant in N = 8 supergravity, which does not require a gauging of the O(8) symmetry, but is rather due to a spontaneous breakdown of supersymmetry.  相似文献   

12.
We present new parametrisations of the parton distribution functions of the photon including the first parametrisation in next-to-leading order QCD. We take into account some recent theoretical considerations pertaining to the gluon content of the photon,g γ. We argue that if an evolution is started at very lowQ 2 and a fit to allF 2 γ data performed with no constraints on the gluon distribution, then physically unreasonable gluon distributions may result. Our results support recent indications thatQ 0 2 ≤1 GeV2 is too low a value from which to start a perturbative evolution. Starting our evolution atQ 0 2 =5.3 GeV2, we evolve up inQ 2 using a modified version of Rossi's Ansatz. The limited lever arm inQ 2 leads to limited sensitivity to the QCD scale parameter Λ, though there is a preference for low values in the 0.1–0.2 GeV range. We also present new parametrisations of the singular asymptotic quark and gluon distribution functions of the photon which we believe are more accurate than those in current use.  相似文献   

13.
It is argued that since in asymptotically free Yang-Mills theories the quantum ground state is not controlled by perturbation theory, there is no a priori reason to believe that individual orbits corresponding to minima of the classical action dominate the Euclidean functional integral. To examine and classify the vacua of the quantum gauge theory, we propose an effective action in which the gauge field coupling constant g is replaced by the effective coupling g(t), t = ln[Fμνa)2μ4]. The vacua of this model correspond to paramagnetism and perfect paramagnetism, for which the gauge field is Fμνa = 0, and ferromagnetism, for which (Fμνa)2 = λ2, i.e. spontaneous magnetization of the vacuum occurs. We show that there are no instanton solutions to the quantum effective action. The equations for a point classical source of color spin are solved, and we show that the field infrared energy becomes linearly divergent in the limit of spontaneous magnetization. This implies bag formation, and an electric Meissner effect confining the bag contents.  相似文献   

14.
《Physics letters. [Part B]》1986,178(1):105-109
A number of authors have investigated mass inequalities for mesons and baryons in QCD. These provide rigorous non-perturbative constraints on the mass spectrum. Similar inequalities for glueballs are investigated. For nonzero spin J, in the large-Nc approximation, mJmJ+ is found. (For J = 0, the existence of a gluon condensate can modify this statement.) There are also constraints on how fast mJ can grow with J. For example, for mJ = a + bJα, 0 ⩽ α ⩽ 1 is found, a result consistent with Regge behaviour.  相似文献   

15.
We argue that the radiative energy loss of a parton traversing the quark–gluon plasma is determined by Landau damping of soft modes in the plasma. Using this idea, we calculate the jet quenching parameter of a gluon. The calculation is done in SU(3) quenched QCD within the stochastic vacuum model. At the LHC-relevant temperatures, the result depends on the gluon condensate, the vacuum correlation length, and the gluon Debye mass. Numerically, when the temperature varies from T=Tc to T = 900 MeV, the jet quenching parameter rises from to approximately 1.8 GeV2/fm. We compare our results with the predictions of perturbative QCD and other calculations.  相似文献   

16.
17.
We analyse the restrictions imposed by supersymmetric Ward identities on the dimension-six condensates in supersymmetric gluodynamics. It is shown that the system of the Ward identities admits a nonzero value for the four-fermion condensate \(\left\langle {\left( {\lambda \sigma _\mu T^a \bar \lambda } \right)^2 } \right\rangle _0 \) while 〈f abc F μν a F νρ b F ρμ c 0 must vanish.  相似文献   

18.
《Physics letters. [Part B]》1986,173(2):179-183
A recently developed method of momentum-space Monte Carlo is applied to compute the momentum-space gluon propagator in quenched, reduced, continuum QCD3 in axial gauge. There is some evidence that the gluon propagator Dμν(p) is finite as p → 0, which might indicate the existence of a non-perturbative gluon mass.  相似文献   

19.
Nonperturbative QCD vacuum with two light quarks at finite temperature was studied in a hadron resonance-gas model. Temperature dependences of the quark and gluon condensates in the confined phase were obtained. It is shown that the quark condensate and one-half (chromoelectric component) of the gluon condensate are evaporated at the same temperature corresponding to the quark-hadron phase transition. With allowance for the temperature shift of hadron masses, the critical temperature was found to be T c ?190 MeV.  相似文献   

20.
The norperturbative QCD vacuum at finite temperature in a external magnetic field is studied. Equations that relate nonperturbative QCD condensates at finite temperature to the thermodynamic pressure at T ≠ 0 and H ≠ 0 are obtained, and low-energy theorems are derived. The free energy of the QCD vacuum in the hadronic phase at H ≠ 0 is calculated, and expressions for the quark and gluon condensates are obtained. Various limiting cases for the behavior of the condensates at low and high temperatures and in weak and strong magnetic fields are investigated. A new interesting phenomenon that consists in the freezing of the quark condensate by a magnetic field is found. The character of spontaneous chiral-symmetry breaking in finite-temperature QCD in a magnetic field is studied. For this purpose, the Gell-Mann-Oakes-Renner formula relating the pion mass M π and the axial-vector coupling constant F π to the quark condensate is derived at T ≠ 0 and H ≠ 0. It is shown that this formula preserves its form at finite temperature after taking into account a magnetic field—that is, no additional terms independent of T and H appear. Thus, the scheme of soft chiral-symmetry breaking remains unchanged. The quark-hadron phase transition in QCD in a magnetic field is studied. It is shown that the phase-transition temperature becomes lower than that in the case of zero magnetic field.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号