arXiv subjects

Lei Wang

Publications and source records attributed to Lei Wang.

1,379 records · Page 77Linked to original sources

arXiv2005

Interface thermal resistance between dissimilar anharmonic lattice

We study interface thermal resistance (ITR) in a system consisting of two dissimilar anharmonic lattices exemplified by Fermi-Pasta-Ulam (FPU) model and Frenkel-Kontorova (FK) model. It is found that the ITR is asymmetric, namely, it depends on how the temperature gradient is applied. The dependence of the ITR on the coupling constant, temperature, temperature difference, and system size are studied. Possible applications in nanoscale heat management and control are discussed.

cond-mat.dis-nn↗

arXiv2005

Littlest Higgs model and top-charm production at high-energy linear colliders

Due to the presence of extra top quark T in the little Higgs models, the $CKM$ matrix is not unitary and the flavor changing neutral currents may exist at the tree level. In the context of the Littlest Higgs(LH) model, we discuss the top-charm production at the high-energy linear $e^{+}e^{-}$ collider $(LC)$ via the processes $e^{+}e^{-}\to \bar{t}c +t\bar{c}$, $e^{+}e^{-}\to (\bar{t}c +t\bar{c})ν_{e}\bar{ν_{e}}$, and $e^{-}γ\to e^{-}\bar{t}c$. We find that the resonance production cross section for the process $e^{+}e^{-}\to \bar{t}c+ t\bar{c} $ is significantly larger, which can be detected in future $LC$ experiments.

hep-ph↗

arXiv2005

New gauge bosons from the littlest Higgs model and the process $e^{+}e^{-}\to t\bar{t}$

In the context of the littlest Higgs$(LH)$ model, we study the process $ e^{+}e^{-}\to t\bar{t}$. We find that the new gauge bosons $Z_{H}$ and $B_{H}$ can produce significant correction effects on this process, which can be further enhanced by the suitably polarized beams. In most of the parameter space preferred by the electroweak precision data, the absolute value of the relative correction parameter $R_{B_{H}}$ is larger than 5%. As long as $1TeV\leq M_{Z_{H}}\leq 1.5TeV$ and $0.3\leq c\leq 0.5,$ the absolute value of the relative correction parameter $R_{Z_{H}}$ is larger than 5%. With reasonable values of the parameters of the $LH$ model, the possible signals of the new gauge bosons $B_{H}$ and $Z_{H}$ can be detected via the process $ e^{+}e^{-} \to t\bar{t}$ in the future $LC$ experiments with the c.m. energy $\sqrt{S}=800GeV$. $B_{H}$ exchange and $Z_{H}$ exchange can generate significantly corrections to the forward-backward asymmetry $A_{FB}(t\bar{t})$ only in small part of the parameter space.

hep-ph↗

arXiv2004

Thermal diode: Rectification of heat flux

By coupling two nonlinear one dimensional lattices, we demonstrate a thermal diode model that works in a wide range of system parameters. We provide numerical and analytical evidence for the underlying mechanism which allows heat flux in one direction while the system acts like an insulator when the temperature gradient is reversed. The possible experimental realization in nano scale systems is briefly discussed.

cond-mat.dis-nn↗

arXiv2004

Anomalous heat conduction and anomalous diffusion in nonlinear lattices, single walled nanotubes, and billiard gas channels

We study anomalous heat conduction and anomalous diffusion in low dimensional systems ranging from nonlinear lattices, single walled carbon nanotubes, to billiard gas channels. We find that in all discussed systems, the anomalous heat conductivity can be connected with the anomalous diffusion, namely, if energy diffusion is $σ^2(t)\equiv <Δx^2> =2Dt^α (0<α\le 2)$, then the thermal conductivity can be expressed in terms of the system size $L$ as $κ= cL^β$ with $β=2-2/α$. This result predicts that a normal diffusion ($α=1$) implies a normal heat conduction obeying the Fourier law ($β=0$), a superdiffusion ($α>1$) implies an anomalous heat conduction with a divergent thermal conductivity ($β>0$), and more interestingly, a subdiffusion ($α<1$) implies an anomalous heat conduction with a convergent thermal conductivity ($β<0$), consequently, the system is a thermal insulator in the thermodynamic limit. Existing numerical data support our theoretical prediction.

cond-mat.stat-mech↗

arXiv2004

Neutral top-pion and the rare top decays $t\to c l_{i} l_{j}$

We study the rare top decays $t\to c l_{i} l_{j}(l=τ,μ,or e)$ in the framework of topcolor-assisted technicolor($TC2$) models. We find that the neutral top-pion $π_{t}^{0}$ can produce significant contributions to these processes via the flavor changing couplings $π_{t}^{0} \bar{t} c$ and $π_{t}^{0} l_{i} l_{j}$. For the $π_{t}^{0}$ mass $m_{π_{t}}=150 GeV$ and the parameter $ε=0.08$, the branching ratio $Br$(t$\to c ττ)$ can reach $7.1\times10^{-7}$. Taking into account the constraints of the present experimental limit of the process $μ\to e γ$ on the free parameters of $TC2$ models, we find that the value of $Br$($t\to c τμ$)$\approx$$Br$($t\to c τe$) is in the range of 1.8$\times10^{-10}\sim1.7\times10^{-8}$.

hep-ph↗

arXiv2003

Phase diffusion of Bose-Einstein condensates in a one-dimensional optical lattice

We investigate the phase diffusion of a Bose-Einstein condensate (BEC) confined in the combined potential of a magnetic trap and a one-dimensional optical lattice. We show that the phase diffusion of the condensate in the whole optical lattice is evident and can be measured from the interference pattern of expanding subcondensates after the optical lattice is switched off. The maximum density of the interference pattern decreases significantly due to the mixing of the phase diffusion appearing in different subcondensates. This suggests a way to detect experimentally the notable phase diffusion of BECs.

cond-mat.soft↗

arXiv2002

Finite thermal conductivity in 1D models having zero Lyapunov exponents

Heat conduction in three types of 1D channels are studied. The channels consist of two parallel walls, right triangles as scattering obstacles, and noninteracting particles. The triangles are placed along the walls in three different ways: (a) periodic, (b) disordered in height, and (c) disordered in position. The Lyapunov exponents in all three models are zero because of the flatness of triangle sides. It is found numerically that the temperature gradient can be formed in all three channels, but the Fourier heat law is observed only in two disordered ones. The results show that there might be no direct connection between chaos (in the sense of positive Lyapunov exponent) and the normal thermal conduction.

cond-mat.stat-mech↗

arXiv2001

A cellular automaton traffic flow model between the Fukui-Ishibashi and Nagel-Schreckenberg models

We propose and study a new one-dimensional traffic flow cellular automaton (CA) model of high speed vehicles with the Fukui-Ishibashi-type acceleration for all cars and the Nagel-Schreckenberg-type (NS) stochastic delay only for the cars following the trail of the car ahead. The main difference in the delay scenario between the new model and the NS model is that a car with spacing ahead longer than the velocity limit $M$ may not be delayed in the new model. By using a car-oriented mean field theory, we derive the fundamental diagrams of the average speed as the function of car density analytically. Our theoretical results are in excellent agreement with numerical simulations.

cond-mat.stat-mech↗

arXiv1998

Analytical Results For The Steady State Of Traffic Flow Models With Stochastic Delay

Exact mean field equations are derived analytically to give the fundamental diagrams, i.e., the average speed - car density relations, for the Fukui-Ishibashi one-dimensional traffic flow cellular automaton model of high speed vehicles $(v_{max}=M>1) $ with stochastic delay. Starting with the basic equation describing the time evolution of the number of empty sites in front of each car, the concepts of inter-car spacings longer and shorter than $M$ are introduced. The probabilities of having long and short spacings on the road are calculated. For high car densities $(ρ\geq 1/M)$, it is shown that inter-car spacings longer than $M$ will be shortened as the traffic flow evolves in time, and any initial configurations approach a steady state in which all the inter-car spacings are of the short type. Similarly for low car densities $(ρ\leq 1/M)$, it can be shown that traffic flow approaches an asymptotic steady state in which all the inter-car spacings are longer than $M-2$. The average traffic speed is then obtained analytically as a function of car density in the asymptotic steady state. The fundamental diagram so obtained is in excellent agreement with simulation data.

cond-mat↗

arXiv1995

Quasi-calssical approach to two-level systems with dissipation

The quantum dynamics of two-level systems under classical oscillator heat bath is mapped to the classical one of a charged particle under harmonic oscillator potential plus a magnetic field in a plane. The behavior of eigenstates and tunneling and localization are studied in detail. The broken symmetry condition and Langevin-like dissipative equation of motion are obtained. Some special dynamic features are considered.

cond-mat↗