Electron-phonon coupling and a polaron in the t-J model: from the weak to the strong coupling regime

We present numeric results for ground state and angle resolved photoemission spectra (ARPES) for a single hole in the t-J model coupled to optical phonons. The systematic-error-free diagrammatic Monte Carlo method is employed where the Feynman graphs for the Matsubara Green function in imaginary time are summed up completely with respect to phonon variables, while magnetic variables are subjected to the noncrossing approximation. We obtain that at electron-phonon coupling constants relevant for high T(c) cuprates the polaron undergoes a self-trapping crossover to the strong-coupling limit and theoretical ARPES demonstrate features observed in experiment: A broad peak in the bottom of the spectra has momentum dependence which coincides with that of a hole in the pure t-J model.     

Transition from strong to weak coupling in SU(N) lattice gauge theories

A possible explanation is proposed for the crossover from strong to weak coupling region in SU(N) lattice gauge theories. We predict the pointswhere the crossover takes place for all SU(N)M: For example, g² ≈ 2.0 for SU(2), g² ≈ 1.0 for SU(3) and lim_N→∞Ng²(SU(N) ≈ 2.0.     

Measurements of the strong coupling constant and the QCD colour factors using four-jet observables from hadronic Z decays

Data from annihilation into hadrons, taken with the ALEPH detector at the Z resonance, are analyzed. The four-jet rate is studied as a function of the resolution parameter and compared to next-to-leading order calculations combined with resummation of large logarithms. Angular correlations in four-jet events are measured and compared to next-to-leading order QCD predictions. With these observables two different measurements are performed. In a first analysis the strong coupling constant is measured from the four-jet rate yielding . In a second measurement the strong coupling constant and the QCD colour factors are determined simultaneously from a fit to the four-jet rate and the four-jet angular correlations, giving in good agreement with the expectation from QCD. Received: 14 May 2002 / Published online: 15 January 2003     

Variation of jet quenching from RHIC to LHC and thermal suppression of the QCD coupling constant

We perform a joint jet tomographic analysis of the data on the nuclear modification factor R _AA from PHENIX at RHIC and ALICE at LHC. The computations are performed accounting for radiative and collisional parton energy loss with running coupling constant. Our results show that the observed slow variation of R _AA from RHIC to LHC indicates that the QCD coupling constant is suppressed in the quark-gluon plasma produced at LHC.     

强弱耦合板-腔系统的声辐射模态计算与分析EI北大核心CSCD

针对板-腔耦合系统的声辐射模态(ARM)计算问题,提出了一种基于能量原理的声辐射模态计算方法,该方法从能量原理的动力学方程构建起声压模态幅值和结构模态幅值的关系,通过将声势能表示为结构模态幅值向量的二次型形式,得到板-腔耦合系统的声辐射模态,弥补了前人理论在解决声腔为阻抗壁面和结构-声为强耦合条件时的不足。通过数值算例验证了本文计算方法的正确性和有效性,在此基础上分析了壁面和结构-声耦合条件变化对声辐射模态特性的影响。结果表明:声辐射模态辐射效率曲线会在声腔模态频率处产生峰值,阻抗壁面的引入会降低声辐射模态辐射效率在峰值处的幅值,并且阻抗值越小,幅值衰减效应越明显,具体表现为声势能曲线在辐射效率峰值频率处幅值会下降;强耦合条件下低频段声势能响应主要由弹性板结构模态激发,响应峰值密度更高,幅值更低。低频同频宽的声辐射模态辐射效率峰值数更少,峰值频率更高。     

Calculation and analysis for acoustic radiation mode of strong and weak plate-cavity coupling systems

A method based on the energy principle is proposed for calculating the acoustic radiation mode of plate-cavity coupling systems.The relationship between the acoustic pressure mode amplitude vector and the structural mode amplitude vector is constructed according to the kinetics equations based on the energy principle.The acoustic radiation mode of plate-cavity coupling systems is derived by expressing the acoustic potential energy as a quadratic form of the structural mode amplitude vector.The p...     

Predictions for the weak leptonic baryon form factors from the hybrid groupSU 3⊗SU 3⊗U 1

Relations between the form factors of the weak leptonic baryon interaction are obtained from invariance under the groupSU ₃?SU ₃?U ₁. The weak interaction operatorV _μ ?A _μ is assumed to behave like the corresponding components of representations35 ofSU ₆ with different parities. One gets the result that the well-known predictions of the staticSU ₆ theory, viz., pureF-coupling for the vector- and 3D+2F-coupling for the axial-vector part, are only valid in the limit of vanishing momentum transfer. In the same limit the resultC _A /C _V =?\(\tfrac{5}{3}\) is obtained if one further assumes thatV ₀ and\(\vec A\) belong to thesame representation35 ofSU ₆.     

A three-soliton structure with strong and weak coupling in a wide-aperture laser with saturable absorption

A soliton complex consisting of three laser solitons is found with the help of numerical simulation of the spatiotemporal structure of the field in a wide-aperture class-A laser with saturable absorption in the mean field approximation with respect to the longitudinal coordinate. Two solitons are strongly coupled and rotate, whereas the third one is weakly coupled with this pair of solitons and revolves around it with a smaller angular velocity. A phase portrait of transverse energy fluxes of radiation that corroborates this type of coupling between the solitons is presented.     

Comparing the weak and strong gate‐coupling regimes for nanotube and graphene transistors

We present an experimental and theoretical comparison of the weak and strong gate‐coupling regimes that arise for carbon nanotube (CNT) and graphene field‐effect transistors (FETs) in back‐gated and liquid‐gated configuration, respectively. We find that whereas the back‐gate efficiency is suppressed for a liquid‐gated CNT FET, the back gate is still effective in case of a liquid‐gated graphene FET. We calculate the gate‐induced Fermi‐level shifts and induced charge densities. In both strong and weak coupling regimes, nonlinearities occur in the gate dependence of these parameters, which can significantly influence the electronic transport. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Transition from weak to strong coupling in QCD and in grand unified models at high temperature

We investigate the weak-coupling expansion at high temperature for relativistic quantum field theories. Boson self-energies generally acquire a non-analytic dependence on the coupling due to the infrared plasmon effect. We show how to sum loops within loops for such thermodynamic quantities as pressure and energy density. Recent high-precision Monte Carlo simulations of quarkless SU(3) gauge theory are compared to the weak-coupling expansion and an excellent agreement is obtained for the high-temperature phase. Weak-coupling calculations are also carried out for supersymmetric grand unified models. We find indications that such models are often strongly coupled already at the unification temperature. This may have a significant effect on models of the early universe.     

Intermediate coupling model of cuprates: Adding fluctuations to a weak coupling model of pseudogap and superconductivity competition

We demonstrate that many features ascribed to strong correlation effects in various spectroscopies of the cuprates are captured by a calculation of the self-energy incorporating effects of spin and charge fluctuations. The self-energy is calculated over the full doping range from half-filling to the overdoped system. In the normal state, the spectral function reveals four subbands: two widely split incoherent bands representing the remnant of the two Hubbard bands, and two additional coherent, spin- and charge-dressed in-gap bands split by a spin-density wave, which collapses in the overdoped regime. The resulting coherent subbands closely resemble our earlier mean-field results. Here we present an overview of the combined results of our mean-field calculations and the newer extensions into the intermediate coupling regime.     

Jet quenching parameter from a soft wall AdS/QCD model

We study the effect of chemical potential and nonconformality on the jet quenching parameter in a holographic QCD model with conformal invariance broken by background dilaton. The presence of chemical potential and nonconformality both increase the jet quenching parameter, thus enhancing the energy loss, consistently with the findings of the drag force.     

Dynamics of the transition from strong to weak coupling regime in a system of exciton polaritons in semiconductor microcavities

The dynamics of polaritonic emission of a GaAs-based microcavity with embedded quantum wells under nonresonant optical excitation is studied. Kinetic dependences of the intensity, spectral position, and linewidth of spontaneous and stimulated emission of the microcavity are measured. It is established that the dynamics of the high-frequency shift of the emission line is qualitatively similar to the dynamics of the emission intensity, but the spectral shift attains its maximum value before the peak intensity is reached. The emission linewidth is maximal immediately after the excitation pulse. Under the conditions of spontaneous emission, the linewidth decreases steadily with time, approaching the value corresponding to low polariton densities. Under lasing conditions, the linewidth is at a minimum when the stimulated-emission intensity attains its peak value. The experimental data are analyzed on the basis of a theoretical model that describes relaxation processes taking into account exciton-exciton and exciton-free carrier interactions.     

A spin-dependent Popov-Fedotov trick and a new loop expansion for the strong coupling negativeU Hubbard model

We calculate fluctuation effects on Bose condensation type superconductivity in the strong coupling negative U Hubbard model by means of a new loop expansion. Our method is based on a spin-dependent modification of the Popov-Fedotov trick. We replace the Popov-Fedotov chemical potential by a fictitious imaginary magnetic field. This field is absorbed in spindependent semionic Matsubara frequencies, which allows for a mixed statistics representation of the anisotropic quantum spin 1/2 Heisenberg model. We report results at one loop order for the superconducting order parameter , for the critical temperature, for the chemical potential, and for the excitation spectra both above and belowT _c. We identify mean field results in zeroth loop order and we find both dimensional and filling (v-)depending singularities in interaction fluctuations at one loop order. Renormalization of dimensional singularities is carried out in 4 dimensions. Divergencies withv (1–v)0 in the dilute limits indicate the breakdown of mean field solutions, but superconductivity persists for arbitrarily smallv(1–v) if our loop expansion is interpreted by exponential behaviour as it is suggested by the abelian nonlinear sigma model.     

Some exact results for the spin-1/2 Falicov-Kimball model in the strong coupling limit

The spin-1/2 Falicov-Kimball model for electronically driven valence and metal-insulator transitions is studied analytically using strong-coupling perturbation theory. It is shown that in the limit of the infinite interaction strength between localized and itinerant electrons the Falicov-Kimball model undergoes two types of discontinuous valence transitions: the insulator-metal transitions from an integer-valence ground state (n _f = 1) into an inhomogeneous intermediate-valence ground state (0 < n _f < 1) and the insulator-metal transitions from n _f = 1 to n _f = 0. In addition, we discuss the role of the electron-phonon interaction on the mechanism of valence transitions and we present possible extensions of the exact one dimensional results to higher dimensions.     

用不变量方法解具有非线性场和原子与场非线性耦合的Jaynes-Cummings模型

采用Lewis-Riesenfeld不变量方法研究了具有非线性场和任意形式原子与场相互作用的Jaynes-Cummings模型.该模型由于具有超对称代数结构,因此其Hamiltonian量可用超对称算符的线性组合表示.在算符N′的本征值子空间,用生成元算符构造出系统的不变量后,利用不变量方法求得了系统的一般波函数和时间演化算符,同时也计算了原子布居数和光子数的时间演化表达式.     

On the link between strong and weak coupling expansions for the SU(2) lattice gauge theory

The intermediate region between the strong and weak coupling expansions of SU(2) lattice gauge theory is analyzed by inverting the strong coupling series of the average plaquette energy E_p(J).

Taking into account the weak coupling behaviour too, we get Padé approximants for J(E_p) valid in the whole physical region. The zeros of pJ/pE_p are mapped into singularities of E_p(J); they occur for complex values of J and give rise to a peak in the specific heat in fair agreement with the Monte Carlo simulation data. The variable E_p is further used to analyze the strong coupling expansions for the roughening indicator, the string tension and the mass gap.     

High-fidelity quantum state transfer and strong coupling in a hybrid NV center coupled to CPW cavity system

A scheme is proposed for quantum state transfer from the cavity field to the micromechanical cantilever and the realization of strong coupling. Our results show that a reliable high-fidelity quantum state transfer can be realized by modulating the system coefficients. Meanwhile, the strong coupling between the micromechanical cantilever and the CPW cavity has been generated via the NV center. Therefore, it is expected that our scheme could be utilized to realize large-scale quantum computation and quantum simulation.     

Constituent quark model for baryons with strong quark-pair correlations and non-leptonic weak transitions of hyperon

We study the roles of quark-pair correlations for baryon properties, in particular on non-leptonic weak decay of hyperons. We construct the quark wave function of baryons by solving the three body problem explicitly with confinement force and the short range attraction for a pair of quarks with their total spin being 0. We show that the existence of the strong quark-quark correlations enhances the non-leptonic transition amplitudes which is consistent with the data, while the baryon masses and radii are kept to the experiment.