HMO model of scalar field in vacuum

In this paper, the HMO model of scalar field in vacuum is developed using the covariant field theory, in which the so-called current density and mass density of optical fluid are obtained and analyzed.     

HMO model of scalar field in vacuum

In this paper, the HMO model of scalar field in vacuum is developed using the covariant field theory, in which the so-called current density and mass density of optical fluid are obtained and analyzed.     

Asymptotic behavior of ω in general quintom model

For the quintom models with arbitrary potential , the asymptotic value of equation of state parameter ω is obtained by a new method. In this method, ω of stable attractors are calculated by using the ratio d ln V/d ln a in asymptotic region. All the known results, have been obtained by other methods, are reproduced by this method as specific examples.     

Masses of charmed hadrons in a five-quark model of ψ particles

Mass equations are obtained for an arbitrary SU(n) group, and the masses of charmed hadrons are calculated in a five-quark model of particles.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 24–28, May, 1977.I thank A. N. Tavkhelidze for continuing interest in the work, and also V. A o Kuz'min and K. G. Chetyrkin for useful discussions.     

HMO model of scalar field in medium and self-focusing

In this paper, the HMO model of scalar field in medium is presented using the general covariant classical theory of scalar field in medium, which is regarded as a curved space-time represented by optical metric model (OMM) and the case of self-focusing is discussed.     

Form factors of η c in light-front quark model

We study the form factors of the η _c meson in the light-front quark model. We explicitly show that the transition form factor of η _c →γ ^? γ as a function of the momentum transfer is consistent with the experimental data by the BaBar collaboration, while the decay constant of η _c is found to be $f_{\eta_{c}}=230.5^{+52.2}_{-61.0}$ and $303.6^{+115.2}_{-116.4}~\mathrm{MeV}$ for $\eta_{c}\sim c\bar{c}$ by using two η _c →γγ decay widths of 5.3±0.5 and 7.2±2.1 keV, given by Particle Data Group and Lattice QCD calculation, respectively.     

Characteristics of critical amplitude of a sinusoidal stimulus in a model neuron

The characteristics of the critical amplitude of a sinusoidal stimulus in a model neuron, Morris－Lecar model, are investigated numerically. It is important in the study of stochastic resonance to determine whether a periodic stimulus is subthreshold or not. The critical amplitude as a function of the stimulus frequency is not a constant, but a curve, which is the boundary between subthreshold and suprathreshold stimulation. It has been considered that this curve is U-shaped in the previous investigations, and this has been accepted as a universal phenomenon. Nevertheless, we think that it is only true for a type of neuron: namely, resonators. Actually, there exists another type of neuron, integrators, which can undergo a saddle-node on invariant circle bifurcation from the rest state to the firing state. For the latter we find that the critical amplitude increases monotonically as the frequency of sinusoidal stimulus is increased. This is shown by way of the Morris－Lecar model. As a consequence, the critical amplitude curve is studied further, and the dynamical mechanisms underlying the change in critical amplitude curve are uncovered. The results of this paper can provide a reference to choose the subthreshold periodic stimulus.     

Absence of pair binding in the U=∞ Hubbard model

We consider the standard Hubbard model in the U= limit. We show that, for any finite lattice with all positive hopping matrix elements, t _i,j >0, the ground state energy of the system containing two particles in excess of half filling plus the energy of the system at half filling is never lower than twice the energy of the system with a single extra particle. Similar results are obtained for holes when the lattice is bipartite. As a byproduct, we obtain a simple alternative proof of Tasaki's generalization of the Nagaoka theorem for non-bipartite lattices (but without the uniqueness clause).     

Regularization of singular terms in the N¯ potential model

We suggest a method of singular terms regularization in a potential model of the N¯ interaction. This method is free from uncertainties related to the usual cut-off procedure and is based on the fact that, in the presence of sufficiently strong short-range annihilation, N and ¯ never approach close enough to each other. In such a case the low-energy scattering is shown to be fully determined by the OBEP tail, while any details of the short-range core of the N¯ interaction are excluded from the observables. The obtained results for S- and P-wave scattering lengths are in agreement with the well-established theoretical models.     

Study of ψ(4415) in the QPC model

Some authors consider the ψ(4415) to be the 4S or 5S excited tate of a cc pair. Starting from this assumption, we study he decays of the ψ(4415) to DD, D^*D^*, D_SD_S, D_S^*D_S^*, and get the corresponding branching ratios in terms of the Quark-Pair-Creation (QPC) model. Compared with the experimental data, we find that the results of 4S state agree much better than those of the 5S state. Therefore, it is more reasonable to assume the ψ(4415) to be a 4S state.     

Phenomenological model of superconductivity in U1−xThxBe13

A phenomenological model taking into account the interaction between superconductivity and the coherence of Kondo screening is introduced. This model describes the main experimental data on UBe₁₃, including the behaviour of T_c in U_1−xTh_xBe₁₃ under ambient and elevated pressures.     

Direction of arrival estimation using array model in time-frequency domain

Time-frequency analysis is combined with array processing to develop a direction of arrival (DOA) estimation method. The array data model is constructed in time-frequency domain by cross time-frequency distribution between the output of a reference sensor and those of two symmetric sub-arrays. Accordingly a subspace method is presented based on the average of two sub-arrays‘ time-frequency data vector model instead of the conventional array model, to estimate DOAs of multiple signals. Because the array data is processed both in spatial domain and 2-D time-frequency domain, the proposed method has an ability to select the signal of interesting, and is suitable for non-stationary signal. Additionally, the method is robust to noise and holds an advantage of low computational load. Simulations are conducted to verify the efficiency of the method and comparision is made with other methods.     

Study of supersolidity in the two-dimensional Hubbard–Holstein model

We derive an effective Hamiltonian for the two-dimensional Hubbard–Holstein model in the regimes of strong electron–electron and strong electron–phonon interactions by using a nonperturbative approach. In the parameter region where the system manifests the existence of a correlated singlet phase, the effective Hamiltonian transforms to a t₁ ? V ₁ ? V ₂ ? V ₃ Hamiltonian for hard-core-bosons on a checkerboard lattice. We employ quantum Monte Carlo simulations, involving stochastic-series-expansion technique, to obtain the ground state phase diagram. At filling 1∕8, as the strength of off-site repulsion increases, the system undergoes a first-order transition from a superfluid to a diagonal striped solid with ordering wavevector \(\vec{Q}\) = (π∕4, 3π∕4) or (π∕4, 5π∕4). Unlike the one-dimensional situation, our results in the two-dimensional case reveal a supersolid phase (corresponding to the diagonal striped solid) around filling 1∕8 and at large off-site repulsions. Furthermore, for small off-site repulsions, we witness a valence bond solid at one-fourth filling and tiny phase-separated regions at slightly higher fillings.     

Anomalous dimensions of high-gradient operators in then-vector model in 2+ε dimensions

The anomalous dimensions of operators with an arbitrary number of gradients are determined for then-vector model ind=2+ dimensions in one-loop order. For those operators which do not vanish ind=2 dimensions all anomalous dimensions can be given explicitly. Among the scalar operators (underO(n) andO(d)) with 2s derivatives there is an operator with the full dimensiony=2(1–s)+(1+s(s–1)/(n–2))+O( ²). Thus similarly as for theQ-matrix model investigated by Kravtsov, Lerner, and Yudson, large positive corrections in one-loop order are obtained for then-vector model. Possible consequences of the corrections are discussed.Dedicated to Professor W. Brenig on the occasion of his 60th birthdayWork supported in part by the Sonderforschungsbereich 123 Stochastic Mathematical Models of the Deutsche Forschungsgemeinschaft     

Control of chaos in Frenkel–Kontorova model using reinforcement learning

It is shown that we can control spatiotemporal chaos in the Frenkel–Kontorova(FK) model by a model-free control method based on reinforcement learning. The method uses Q-learning to find optimal control strategies based on the reward feedback from the environment that maximizes its performance. The optimal control strategies are recorded in a Q-table and then employed to implement controllers. The advantage of the method is that it does not require an explicit knowledge of the system, target states, and unstable periodic orbits. All that we need is the parameters that we are trying to control and an unknown simulation model that represents the interactive environment. To control the FK model, we employ the perturbation policy on two different kinds of parameters, i.e., the pendulum lengths and the phase angles. We show that both of the two perturbation techniques, i.e., changing the lengths and changing their phase angles, can suppress chaos in the system and make it create the periodic patterns. The form of patterns depends on the initial values of the angular displacements and velocities. In particular, we show that the pinning control strategy, which only changes a small number of lengths or phase angles, can be put into effect.     

Quadrupole polarizabilities of the pion in the Nambu–Jona-Lasinio model

The electromagnetic dipole and quadrupole polarizabilities of the neutral and charged pions are calculated in the Nambu–Jona-Lasinio model. Our results agree with the recent experimental analysis of these quantities based on dispersion sum rules. Comparison is made with the results from the chiral perturbation theory.     

Crust-core properties of neutron stars in the Nambu–Jona-Lasinio model

We adopt the Nambu–Jona-Lasinio(NJL) model to study the crust-core transition properties in neutron stars(NSs). For a given momentum cutoff and symmetry energy of saturation density in the NJL model, decreasing the slope of the symmetry energy gives rise to an increase in the crust-core transition density and transition pressure.Given the slope of the symmetry energy at saturation density, the transition density and corresponding transition pressure increase with increasing symmetry energy. The increasing trend between the fraction of the crustal moment of inertia and the slope of symmetry energy at saturation density indicates that a relatively large momentum cutoff of the NJL model is preferred. For a momentum cutoff of 500 Me V, the fraction of the crustal moment of inertia clearly increases with the slope of symmetry energy at saturation density. Thus, at the required fraction(7%) of the crustal moment of inertia, the NJL model with momentum cutoff of 500 Me V and a large slope of the symmetry energy of saturation density can give the upper limit of the mass of the Vela pulsar to be above 1.40 M_⊙.     

Asymptotics of a τ-function arising in the two-dimensional Ising model

The short-distance assymptotics of the -function associated to the 2-point function of the two-dimensional Ising model is computed as a function of the integration constant defined from the long-distance behavior of the -function. The result is expressible in terms of the Barnes double gamma function (equivalently, the BarnesG-function).Supported in part by the National Science Foundation, Grant No. DMS-90-01794     

Biham–Middleton–Levine model in consideration of cooperative willingness

In this paper, the Biham-Middleton-Levine （BML） model with consideration of cooperative willingness has been proposed to study the traffic flow in urban networks. An evolutionary game with a cooperative willingness profile is intro-duced to deal with conflicts between disturbing neighbors. Simulation results suggest that imitating cooperative willingness can ease the effect of premature seizure on traffic flow due to the introduction of evolutionary games. Phase diagrams with a strategy profile and cooperative willingness profile have been investigated in detail. Our findings also prove that by imitating the more successful, cooperative willingness instead of simply the more successful strategies, the evolution of cooperation is significantly promoted, hence improving the order of cooperation and relieving the pressure of traffic networks.