共查询到20条相似文献,搜索用时 46 毫秒
1.
Yu. S. Kalashnikova I. M. Narodetskii 《Zeitschrift fur Physik C Particles and Fields》1989,43(2):273-278
We have examined the \(c^2 \bar c^2 \) system in the context of additive quark potential model using an extended variational ansatz for the multiquark wave function that includes both meson-meson component and the admixture of the four-quark confined states. The latter were shown to generate a mechanism for the short-range meson-meson interaction that can produce resonances or even bound states in the four-quark systems. A quantitative effect of this mechanism is studied for a model with harmonic oscillator confinement and for the “Coulomb plus linear” model. In both cases, we find the 2++ resonance in the mass region 6.5–6.6 GeV with Γ=100?200 MeV, depending of the choice of the model parameters. 相似文献
2.
We study meson-meson interactions using an extended q
2
[`(q)]2 (g)\bar q^2 (g) basis that allows calculating coupling of an ordinary meson-meson system to a hybrid-hybrid one. We use a potential model
matrix in this extended basis which at quark level is known to provide a good fit to numerical simulations of a q
2
[`(q)]2\bar q^2 system in pure gluonic theory for static quarks in a selection of geometries. We use a combination of resonating group method
formalism and Born approximation to include the quark motion using wave functions of a q[`(q)]q\bar q potential within a cluster. This potential is taken to be quadratic for ground states and has an additional smeared $\frac{1}
{r}$\frac{1}
{r} (Gaussian) for the matrix elements between hybrid mesons. For the parameters of this potential, we use values chosen to 1)
minimize the error resulting from our use of a quadratic potential and 2) best fit the lattice data for differences of Σ
g
and Π
u
configurations of the gluonic field between a quark and an antiquark. At the quark (static) level, including the gluonic
excitations, was noted to partially replace the need for introducing many-body terms in a multiquark potential. We study how
successful such a replacement is at the (dynamical) hadronic level of relevance to actual hard experiments. Thus we study
the effects of both gluonic excitations and many-body terms on mesonic transition amplitudes and the energy shifts resulting
from the second-order perturbation theory (i.e. from the respective hadron loops). The study suggests introducing both energy and orbital excitations in wave functions of
scalar mesons that are modelled as meson-meson molecules or are supposed to have a meson-meson component in their wave functions. 相似文献
3.
We study charmonium (c(c)n(n)), bottomonium (b(b)n(n)) and exotic (cc(n)(n) and bb(n)(n)) four-quark states by means of a standard non-relativistic quark potential model. We look for possible bound states. Among them we are able to distinguish between meson-meson molecules and compact four-quark states. 相似文献
4.
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
5.
建立了一个夸克交换模型和提出了一个夸克-反夸克湮灭模型来研究介子-介子散射。从量子色动力学我们得到一个依赖于温度的夸克作用势。从微扰量子色动力学推导对应于夸克-反夸克湮灭和产生的跃迁势。模型给出基态介子质量的实验值,并且在玻恩近似下能说明真空中阈能附近的π-π弹性散射相移的实验值。从S矩阵元出发,推导散射的跃迁振幅和截面公式。计算出涉及π,ρ,K,K*的反应的非极化截面。发现这些截面具有强烈的温度依赖性。We have established a quark-interchange model and have proposed a quark-antiquark annihilation model to study meson-meson scattering. From QCD we obtain a temperature-dependent quark potential. The transition potential corresponding to quark-antiquark annihilation and creation is derived in perturbative QCD. The experimental ground-state meson masses are reproduced and the experimental data of elastic phase shifts for ππ scattering near the threshold energy in vacuum can be accounted for in the Born approximation. Starting from S-matrix element, we derive the transition amplitude and the cross section for the scattering. Unpolarised cross sections for reactions involving π, ρ, K and K* are calculated. Remarkable temperature dependence of the cross sections is found. 相似文献
6.
Yu -Qi Li Xiao -Ming Xu Hui -Jun Ge 《The European Physical Journal A - Hadrons and Nuclei》2011,47(5):65
We divide the cross-section for a meson-meson reaction into three parts. The first part is for the quark-interchange process,
the second for quark-antiquark annihilation processes and the third for resonant processes. Master rate equations are established
to yield time dependence of fugacities of pions, rhos, kaons and vector kaons. The equations include cross-sections for inelastic
scattering of pions, rhos, kaons and vector kaons. Cross-sections for quark-interchange-induced reactions, that were obtained
in a potential model, are parametrized for convenient use. The number densities of π and ρ (K and K
* are altered by quark-interchange processes in equal magnitudes but opposite signs. The master rate equations combined with
the hydrodynamic equations for longitudinal and transverse expansion are solved with many sets of initial meson fugacities.
Quark-interchange processes are shown to be important in the contribution of the inelastic meson-meson scattering to the evolution
of mesonic matter. 相似文献
7.
We describe s-wave collisions between ultracold 23Na and 87Rb atoms in the presence of a magnetic field. For any collision input channel knowledge of the singlet and triplet intermolecular potentials [1] enables us to predict the variation in scattering lengths as a function of the magnetic field. We employ the Born-Oppenheimer approximation to predict several Feshbach resonances for 23Na87Rb. We also include a discussion of why these resonances are expected to be narrow as observed in the case of 87Rb2.Received: 6 August 2004, Published online: 23 November 2004PACS:
34.90. + q Other topics in atomic collisions - 03.75.Hh Multicomponent condensates 相似文献
8.
The orthogonality-condition model (OCM), as an approximation method for calculating the overlap and potential overlap functions involved in the form factor of transfer reactions, is tested against microscopic cluster calculations for the 7Li = α + t system. The OCM overlap and potential overlap turn out to depend strongly on the OCM potential although the potentials are chosen so as to produce the same asymptotic phase. Excellent approximations to microscopic overlaps and potential overlaps are, however, obtained by optimizing the OCM potential, so that the OCM may reproduce the microscopic energy surface. In this way the dependence on the OCM potential is traced back to the underlying nucleon-nucleon force. 相似文献
9.
Motivated by the recent measurement of a low longitudinal polarization fraction in the decay mode
, which appears not to be in agreement with the standard model expectation, we analyze this mode in the minimal supersymmetric
standard model with the mass insertion approximation. Within the standard model, with the factorization approximation, the
longitudinal polarization is expected to be
. We find that this anomaly can be explained in the minimal supersymmetric standard model with either the LR or the RL mass insertion approximation.
PACS. 13.25.Hw, 11.30.Er, 12.60.Jv
Received: 9 May 2005, Revised: 26 July 2005, Published online: 30 August 2005 相似文献
10.
A. Ster M. Csanád T. Csörgő B. Lörstad B. Tomášik 《The European Physical Journal A - Hadrons and Nuclei》2011,47(4):58
We present calculations of elliptic flow and azimuthal dependence of correlation radii in the ellipsoidally symmetric generalization
of the Buda-Lund hydrodynamic model of hadron production in high-energy nuclear collisions. We compare them to data from RHIC
by simultaneous fits to azimuthally integrated invariant spectra of pions, kaons and protons-antiprotons measured by PHENIX
in Au + Au reactions at center-of-mass energy of 200 AGeV. STAR data were used for azimuthally sensitive two-particle correlation
function radii and for the transverse momentum dependence of the elliptic flow parameter v
2. We have found that the transverse flow is faster in the reaction plane than out of plane, which results in a reaction zone
that gets slightly more elongated in-plane than out of plane. The model parameters extracted from the fits are shown and discussed. 相似文献
11.
Previous H2 permeation tests showed a degradation of H2 permeation flux with time. To understand the cause of degradation and develop a solution, the stability of $ {\text{SrCe}}_{{0.9}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ and $ {\text{SrZr}}_{{0.2}} {\text{Ce}}_{{0.7}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ samples were studied under dry and wet H2 atmospheres. Total conductivity of $ {\text{SrCe}}_{{0.9}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ increased with time in dry H2. The X-ray diffraction pattern of $ {\text{SrCe}}_{{0.9}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ after dry hydrogen atmosphere heat treatments show CeO2 peaks indicating that $ {\text{SrCe}}_{{0.9}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ decomposes under dry H2 atmospheres; scanning electron microscopy and energy dispersive X-ray spectroscopy analyses prove that decomposition proceeded along the grain boundaries. $ {\text{SrZr}}_{{0.2}} {\text{Ce}}_{{0.7}} {\text{Eu}}_{{0.1}} {\text{O}}_{{3 - \delta }} $ was investigated and demonstrated greater stability under dry hydrogen atmospheres. However, Zr substitution results in a tradeoff with electrical properties. 相似文献
12.
S. Franz T. Garel H. Orland 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,11(3):463-468
We consider a model of two (fully) compact polymer chains, coupled through an attractive interaction. These compact chains
are represented by Hamiltonian paths (HP), and the coupling favors the existence of common bonds between the chains. We use
a (n=0 component) spin representation for these paths, and we evaluate the resulting partition function within a homogeneous saddle
point approximation. For strong coupling (i.e. at low temperature), one finds a phase transition towards a “frozen” phase where one chain is completely adsorbed onto the
other. By performing a Legendre transform, we obtain the probability distribution of overlaps. The fraction of common bonds
between two HP, i.e. their overlap q, has both lower () and upper () bounds. This means in particular that two HP with overlap greater than coincide. These results may be of interest in (bio)polymers and in optimization problems.
Received 4 December 1998 and Received in final form 10 March 1999 相似文献
13.
J. Haidenbauer 《The European Physical Journal A - Hadrons and Nuclei》2007,33(3):287-290
We present a new model for the hyperon-nucleon (ΛN , ΣN interaction, derived within the meson exchange framework. The model incorporates the standard one-boson exchanges of the
lowest pseudoscalar and vector meson multiplets with coupling constants fixed by SU(6) flavor symmetry relations. As a new feature, the contribution in the scalar-isoscalar (σ sector is derived from a microscopic
model of correlated ππ and Kˉ exchange. The same model is also used to constrain the interaction resulting from the vector-isovector (ρ exchange channel.
Additional short-ranged ingredients of the model in the scalar-isovector (a0) and scalar-isospin-1/2 (κ channels are likewise viewed as arising from meson-meson correlations but are treated phenomenologically.
With this model a satisfactory reproduction of the available hyperon-nucleon data is achieved. 相似文献
14.
CHOON KI AHN 《Pramana》2012,78(3):361-374
In this paper, we propose a new adaptive H¥\mathcal H_\infty synchronization strategy, called an adaptive fuzzy delayed feedback H¥\mathcal H_\infty synchronization (AFDFHS) strategy, for chaotic systems with uncertain parameters and external disturbances. Based on Lyapunov–Krasovskii
theory, Takagi–Sugeno (T–S) fuzzy model and adaptive delayed feedback H¥\mathcal H_\infty control scheme, the AFDFHS controller is presented such that the synchronization error system is asymptotically stable with
a guaranteed H¥\mathcal{H}_{\infty } performance. It is shown that the design of the AFDFHS controller with adaptive law can be achieved by solving a linear matrix
inequality (LMI), which can be easily facilitated by using some standard numerical packages. An illustrative example is given
to demonstrate the effectiveness of the proposed AFDFHS approach. 相似文献
15.
We observe that the existence of the S1 and δ just below K threshold has a natural interpretation in the four-quark model for these states, and we apply this interpretation to predict the possible existence of stable four-quark scalar mesons with charm and strangeness. 相似文献
16.
O. Nachtmann 《The European Physical Journal C - Particles and Fields》2003,26(4):579-596
We relate the structure functions of deep inelastic lepton-nucleon scattering to current-current correlation functions in
a Euclidean field theory depending on a parameter r. The r-dependent Hamiltonian of the theory is P
0
-(1-r)P
3
, with P0 the usual Hamiltonian and P3 the third component of the momentum operator. We show that a small in the structure functions corresponds to the small r limit of the effective theory. We argue that for there is a critical regime of the theory where simple scaling relations should hold. We show that in this framework Regge
behaviour of the structure functions obtained with the hard pomeron ansatz corresponds to a scaling behaviour of the matrix
elements in the effective theory where the intercept of the hard pomeron appears as a critical index. Explicit expressions
for various analytic continuations of the structure functions and matrix elements are given as well as path integral representations
for the matrix elements in the effective theory. Our aim is to provide a framework for truly non-perturbative calculations
of the structure functions at small for arbitrary Q2.
Received: 16 July 2002 / Published online: 9 December 2002
RID="a"
ID="a" e-mail: O.Nachtmann@thphys.uni-heidelberg.de 相似文献
17.
A two component model of negative U centers coupled with the Fermi sea of itinerant fermions is discussed in connection with high-temperature superconductivity of cuprates, and superfluidity of atomic fermions. We examine the phase transition and the condensed state of this boson-fermion model (BFM) beyond the ordinary mean-field approximation in two and three dimensions. No pairing of fermions and no condensation are found in two-dimensions for any symmetry of the order parameter. The expansion in the strength of the order parameter near the transition yields no linear homogeneous term in the Ginzburg-Landau-Gorkov equation and a zero upper critical field in any-dimensional BFM, which indicates that previous mean-field discussions of the model are flawed. Normal and anomalous Greens functions are obtained diagrammatically and analytically in the condensed state of a simplest version of 3D BFM. A pairing of bosons analogous to the Cooper pairing of fermions is found. There are three coupled condensates in the model, described by the off-diagonal single-particle boson, pair-fermion and pair-boson fields. These results negate the common wisdom that the boson-fermion model is adequately described by the BCS theory at weak coupling.Received: 26 February 2004, Published online: 18 June 2004PACS:
74.20.-z Theories and models of superconducting state - 74.20.Mn Nonconventional mechanisms (spin fluctuations, polarons and bipolarons, resonating valence bond model, anyon mechanism, marginal Fermi liquid, Luttinger liquid, etc.) - 74.20.Rp Pairing symmetries (other than s-wave) - 74.25.Dw Superconductivity phase diagrams 相似文献
18.
Based on the quark propagator in the instanton dilute liquid approximation, we have determined the nonlocal four-quark condensate at the mean-field level in the framework of global color symmetry model. By making use of this formula, the vacuum susceptibility (pionsusceptibility) was calculated in this paper. The theoretical analysis and numerical calculation show that even at the mean-field level the naive vacuum saturation approximation is not a good approximation when we consider nonlocal four-quark condensate. 相似文献
19.
We propose a self-consistent Ornstein–Zernike approximation for studying the Edwards–Anderson spin glass model. By performing two Legendre transforms in replica space, we introduce a Gibbs free energy depending on both the magnetizations and the overlap order parameters. The correlation functions and the thermodynamics are then obtained from the solution of a set of coupled partial differential equations. The approximation becomes exact in the limit of infinite dimension and it provides a potential route for studying the stability of the high-temperature phase against replica-symmetry breaking fluctuations in finite dimensions. As a first step, we present the predictions for the freezing temperature T
f and for the zero-field thermodynamic properties and correlation length above T
f as a function of dimensionality. 相似文献
20.
The NDDO (neglect of diatomic differential overlap) approximation, a widely used basis for many semi-empirical molecular orbital (MO) approaches, is re-examined based on non-empirical frozen-core calculations on small molecules. An improvement going beyond the NDDO approximation is proposed. Our study shows that under the NDDO approximation, when the remaining non-DDO-type two-electron repulsion integrals (TERIs) are calculated using the basis set from the Löwdin orthogonalization of the valence atomic orbitals, the resulting total energies are much higher than those from the corresponding frozen-core ab initio calculations. On the other hand, when the remaining non-DDO TERIs are calculated using non-orthogonal valence atomic orbitals (similar to the Roby model), for most of the molecules calculated, the total energies are significantly lower than those from the corresponding ab initio calculations. Furthermore, we also find that for some molecules, the total energies thus calculated are higher than the corresponding ab initio results. The nonsystematic variation of the absolute errors in the total energy calculations is due to the fact that the core-electron and the electron-electron interactions are not treated in a balanced way in the NDDO approximation. A new model, which overcomes the deficiencies in the NDDO model, is proposed. In this model, a first-order correction term is added to the electron-electron Coulomb interactions, thereby improving the balance between the core-electron and the electron-electron interactions. Non-empirical test calculations show that the total energies from the new model are consistently higher than those from the ab initio calculation but closer to the ab initio results. We expect that the proposed new model would be useful in developing new high-quality semi-empirical MO approaches. 相似文献