单胶子交换和单π交换夸克模型中核子负宇称共振态的电磁跃迁振幅(英文)

分别利用单胶子交换和单π交换夸克模型计算了核子负宇称激发态的电磁跃迁振幅,讨论了两个模型所给出的不同的组态混合角. 结果表明, 单胶子交换模型所给出的重子波函数比单π交换夸克模型的波函数更为合理.Electromagnetic transition amplitudes of negative parity resonances are calculated based on one pion exchange (OPE) model and one gluon exchange (OGE) model, respectively. The configuration mixing caused by the hyperfine interactions of the two models is discussed. Calculated results for the amplitudes indicate that baryon wave functions of OGE are more reasonable than those of OPE.     

Spectra of charmed and bottom baryons with hyperfine interaction

Up to now,the excited charmed and bottom baryon states have still not been well studied experimentally or theoretically.In this paper,we predict the mass of ?*b,the only L=0 baryon state which has not been observed,to be 6069.2 Me V.The spectra of charmed and bottom baryons with the orbital angular momentum L = 1 are studied in two popular constituent quark models,the Goldstone boson exchange(GBE) model and the one gluon exchange(OGE) hyperfine interaction model.Inserting the latest experimental data from the "Review of Particle Physics",we find that in the GBE model,there exist some multiplets(Σc(b),Ξ c(b)and ?c(b)) in which the total spin of the three quarks in their lowest energy states is 3/2,but in the OGE model there is no such phenomenon.This is the most important difference between the GBE and OGE models.These results can be tested in the near future.We suggest more efforts to study the excited charmed and bottom baryons both theoretically and experimentally,not only for the abundance of baryon spectra,but also for determining which hyperfine interaction model best describes nature.     

Nonlocality effects in the phase diagram of neutral quark matter

We construct phase diagrams of two-flavor quark matter under compact star constraints for two nonlocal, covariant quark models (instanton liquid and one-gluon exchange (OGE) inspired) within the mean field approximation and compare the results for different diquark coupling strengths. For the OGE model, stable hybrid stars with quark cores are obtained. The text was submitted by the authors in English.     

One-gluon exchange corrections to magnetic moments of baryons

One-gluon exchange (OGE) corrections to the magnetic moments of the octet baryons are studied in the bag model. It is clarified that OGE resolves a problem of μ(Λ) and μ(Ξ^?) in previous quark model calculations and also improves an overall agreement between theory and experiment.     

Implications of the ALEPH tau-lepton decay data for perturbative and nonperturbative QCD

We use ALEPH data on hadronic tau decays in order to calculate Euclidean coordinate space correlation functions in the vector and axial-vector channels. The linear combination V-A receives no perturbative contribution and is quantitatively reproduced by the instanton liquid model. In the case of V+A the instanton calculation is in good agreement with the data once perturbative corrections are included. These corrections clearly show the evolution of alpha(s). We also analyze the range of validity of the operator product expansion (OPE). We conclude that the range of validity of the OPE is limited to x less, similar 0.3 fm, whereas the instanton model describes the data over the entire range.     

Fluorescence intensity and anisotropy decays of the DNA stain Hoechst 33342 resulting from one-photon and two-photon excitation

We examined the steady-state and time-resolved fluorescence spectral properties of the DNA stain Hoechst 33342 for one-photon (OPE) and two-photon (TPE) excitation. Hoechst 33342 was found to display a large cross section for two-photon excitation within the fundamental wavelength range of pyridine 2 and rhodamine 6G dye lasers, 690 to 770 and 560 to 630 nm, respectively. The time-resolved measurements show that intensity decays are similar for OPE- and TPE. The anisotropy decay measurements of Hoechst 33342 in ethanol revealed the same correlation times for TPE as observed for OPE. However, the zero-time anisotropies recovered from anisotropy decay measurements are 1.4-fold higher for TPE than for OPE. The anisotropy spectra of Hoechst 33342 were examined in glycerol at ?20°C, revealing limiting values close to the theoretical limits for OPE (0.4) and TPE (0.57). The steady-state anisotropy for OPE decreases in the shorter-wavelength region (R6G dye laser, 280–315 nm), but the two-photon anisotropy for 560 to 630-nm excitation remains as high as in the long-wavelength region (690–770 nm). This result suggests that one-photon absorption is due to two electronic, but only one transition contributes to the two-photon absorption over the wavelength range from 580 to 770 nm. Our demonstration of these favorable two-photon properties for Hoechst 33342, and the high photostability of the dye reported by other laboratories, suggests that this dye will be valuable for time-resolved studies of DNA with TPE and for two-photon fluorescence microscopy.     

Relativistic effects and the constituent quark model of heavy quarkonia

Charmonium \(c\bar c\) and bottomonium \(b\bar b\) are investigated in the framework of a constituent quark model. A scalar confining and a one-gluon exchange (OGE) potential are used in a nonrelativistic reduction to order (p/m)². Therefore the model includes spin dependent as well as spin independent terms. Their influence on the meson mass spectra and decay widths is analysed. We find that the experimental spectra can be reproduced by using a full model as well as by using a reduced version neglecting the spin independent terms. For both versions we calculate leptonic and radiative decay widths including relativistic corrections for the current operators. We find that for leptonic decays inclusion of all terms of the OGE potential gives better results than the non-relativistic formulas. For radiative transitions relativistic corrections are important.     

Axiomatic Quantum Field Theory in Curved Spacetime

The usual formulations of quantum field theory in Minkowski spacetime make crucial use of features—such as Poincaré invariance and the existence of a preferred vacuum state—that are very special to Minkowski spacetime. In order to generalize the formulation of quantum field theory to arbitrary globally hyperbolic curved spacetimes, it is essential that the theory be formulated in an entirely local and covariant manner, without assuming the presence of a preferred state. We propose a new framework for quantum field theory, in which the existence of an Operator Product Expansion (OPE) is elevated to a fundamental status, and, in essence, all of the properties of the quantum field theory are determined by its OPE. We provide general axioms for the OPE coefficients of a quantum field theory. These include a local and covariance assumption (implying that the quantum field theory is constructed in a local and covariant manner from the spacetime metric and other background structure, such as time and space orientations), a microlocal spectrum condition, an “associativity” condition, and the requirement that the coefficient of the identity in the OPE of the product of a field with its adjoint have positive scaling degree. We prove curved spacetime versions of the spin-statistics theorem and the PCT theorem. Some potentially significant further implications of our new viewpoint on quantum field theory are discussed.     

Wilson's operator expansion: Can it fail?

Within the framework of some simple models we discuss the status of the operator product expansion (OPE) in the presence of nonperturbative effects. We consider, in particular, the 4d Higgs model, 2d sigma model and the Schwinger model. The general formulation of OPE is presented and it is demonstrated that there exists a consistent procedure allowing one to define unambiguously both coefficient functions and matrix elements of composite operators. One of the key elements of the procedure is the introduction of an auxiliary parameter, the normalization point μ. For the simplest T-products discussed in the literature earlier we construct the corresponding OPE explicitly. Then we check its validity by comparing the results for the two-point functions with independent direct calculations of the same correlators. Although the general procedure is standard and does not vary from one theory to another, numerically the relative role of perturbative and nonperturbative contributions in vacuum condensates is different in different theories. The two extremes considered are the λ?⁴ theory with no spontaneous breaking of the symmetry and the O(N) sigma model in the limit N → ∞. In the former case there is only perturbative contribution to (?²), while in the latter case the perturbative pieces are suppressed by 1/N factors. Numerically QCD is much closer to the O(N) sigma model in the large-N limit. Comments on specific features of QCD are presented.     

Study for the pentaquark potential in SU(3) lattice QCD

We perform the first study of the static pentaquark (5Q) potential V(5Q) in SU(3) quenched lattice QCD with 16(3) x 32 and beta = 6.0. From the 5Q Wilson loop, V(5Q) is calculated in a gauge-invariant manner, with the smearing method to enhance the ground-state component. V(5Q) is well described by the OGE-plus-multi-Y ansatz: a sum of the one-gluon-exchange (OGE) Coulomb term and the multi-Y-type linear term proportional to the minimal total length of the flux tube linking the five quarks. Comparing with QQ and3Q potentials, we find a universality of the string tension, sigma(QQ) approximately sigma(3Q) approximately sigma(5Q), and the OGE result for Coulomb coefficients.     

OPE molecular junction as a hydrogen gas sensor

Oligo(phenylene ethynylene) (OPE) molecular junction has been suggested as a H₂ molecule sensor based on calculations using the first principles of density–functional theory and non-equilibrium Green's function. The electronic transport properties of the OPE molecule between two Au electrodes with or without adsorbed H₂ molecules are investigated. Results show that the adsorbed H₂ molecule significantly changes the characteristics of the current–voltage curve of the OPE molecular junction. The pure OPE molecular junction exhibits a significant negative differential resistance, but this kind of phenomenon will disappear or weaken after hydrogen molecules are adsorbed. The conductance of the junction also obviously decreases in the bias range of [−0.4, 0.4] V after adsorbing H₂ molecules. These effects can be used to design a H₂ molecule sensor.     

Nonlinear acoustic propagation and focusing

Two model equations of nonlinear acoustics are considered. The implications of a point transformation between forms of the generalised Burgers equation (GBE) is discussed. New exact and asymptotic solutions are obtained. The dissipative Zabolotskaya-Khokhlov (DZK) equation describing acoustic wave propagation with allowance for transverse amplitude variation is studied. By considering a transformation onto the GBE, solutions exhibiting caustic behaviour are presented. A mechanism for the control of such singularities is presented along with a comparison with shock formation time.Department of Applied Mathematics and Theoretical Physics, University of Cambridge, Cambridge CB3 9EW, England. Published in Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 36, No. 8, pp. 783–787, August, 1993.     

A relativistic Hartree-Fock model for quark systems

The “relativistic H—F” scheme is applied to baryons and finite multiquark sustems. A two-body confinement potential (r, r² or r³) and the one-gluon-exchange interaction are incorporated. The electric OGE term is treated consistently in all considered systems. With the electric OGE term included, the solutions indicate the little bag. (Os)-closed multiquark states, strange or non-strange, cannot be lower in energy than an aggregate of Δ or Λ.     

A comment on the interpretation of anomalous enhancements n the reaction p + d → d + missing mass

Difficulties in interpreting the reaction p + d → d + missing mass are discussed. Treating this reaction as a quasi-two-nucleon process, absolute calculations are presented using the OPE model. Comparison is made with other recent calculations.     

Cross polarization effect of donor–acceptor group on a potential single‐molecule transistor

Theoretical investigation of the polarization effect on a potential single‐molecule transistor has been studied with density functional theory. 4,4′‐(2‐Amino‐5‐nitro‐1,4‐phenylene)bis(ethyne‐2,1‐diyl) dibenzenethiol (AN‐OPE), containing a donor and an acceptor (D–A) crossed to its oligo(p‐phenylene‐ethynylene) (OPE) backbone, was used as a prototype for this study. Simulation results indicate that AN‐OPE has a higher on/off ratio on conductance than OPE because of the larger polarization along the D–A direction. This high on/off ratio was proved by the 20 times variation in molecular charge, 15 times variation in bond lengths, 49 times variation in polarizability, 9 times variation in the rotation angles, and 13 times variation in the highest occupied molecular orbital–lowest unoccupied molecular orbital gaps under the same gate using B3LYP/6‐31G (d, p). And results imply that conjugated molecules with a cross D–A structure could be a good direction for constructing a better single‐molecule field‐effect transistor. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis of a Homopolymer of Oligo(p-phenyleneethynylene) Attached to Alternate Carbons of a Main Chain Polyethylene and Its Liquid-Crystalline and Optical Properties

A homopolymer of oligo(p-phenyleneethynylene)s OPE-attached polyethylene (OPE-PE) was prepared through the thermal addition polymerization of the vinyls in a synthesized mono-vinyl end-capped OPE. The liquid-crystalline and optical properties of the synthesized homopolymer of OPE-PE were studied using polarizing optical microscopy (POM), wide-angle X-ray diffraction (WAXD), ultraviolet-visible (UV-vis) absorption, photoluminescence excitation (PLE) and photoluminescence (PL). The results show that the arrangements of the rigid side chains in the homopolymer of OPE-PE are affected by the flexible main chains in both liquid and solid states. Through a suitable treatment of the film, the formation of aggregates and excimers in the solid state can be avoided. This result provides a new method to eliminate the formation of aggregates and excimers in the active layers of organic light-emitting diodes (OLED) devices, and this kind of homopolymer with OPE side chains could be a promising class of light-emitting materials.     

Derivation of bloch equations from the time convolutionless generalized master equation

The generalized Bloch equations (GBE) describing the temporal evolution of a single two-level atom interacting with a classical external field of arbitrary intensity and with a thermodynamic bath are obtained from the time convolutionless generalized master equation or equivalently from the Tokuyama-Mori identity. These GBE are then used to calculate the absorption spectrum of a single two-level atom with frequency modulated by dichotomic noise with time-dependent transition probability.     

Non-perturbative non-locality: V±A correlators in euclidean position space

Using an OPE modification, which takes non-perturbative non-locality into account, the difference and sum of vector and axial-vector correlators are evaluated in euclidean position space. For distances up to 0.8 fm the calculated behavior is close to the instanton liquid result and the ALEPH data, in contrast to the implications of the conventional OPE.