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Register a new user3/4 Fractional superdiffusion of energy in a system of harmonic oscillators perturbed by a conservative noise
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Authors
Cedric Bernardin
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We consider a harmonic chain perturbed by an energy conserving noise and show that after a space-time rescaling the energy-energy correlation function is given by the solution of a skew-fractional heat equation with exponent 3/4.
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We study the transport of heat along a chain of particles interacting through a harmonic potential and subject to heat reservoirs at its ends. Each particle has two degrees of freedom and is subject to a stochastic noise that produces infinitesimal changes in the velocity while keeping the kinetic energy unchanged. This is modelled by means of a Langevin equation with multiplicative noise. We show that the introduction of this energy conserving stochastic noise leads to Fouriers law. By means of an approximate solution that becomes exact in the thermodynamic limit, we also show that the heat conductivity $kappa$ behaves as $kappa = a L/(b+lambda L)$ for large values of the intensity $lambda$ of the energy conserving noise and large chain sizes $L$. Hence, we conclude that in the thermodynamic limit the heat conductivity is finite and given by $kappa=a/lambda$.
We analyze the transport of heat along a chain of particles interacting through anharmonic po- tentials consisting of quartic terms in addition to harmonic quadratic terms and subject to heat reservoirs at its ends. Each particle is also subject to an impulsive shot noise with exponentially distributed waiting times whose effect is to change the sign of its velocity, thus conserving the en- ergy of the chain. We show that the introduction of this energy conserving stochastic noise leads to Fourier law. The behavior of thels heat conductivity for small intensities of the shot noise and large system sizes are found to obey a finite-size scaling relation. We also show that the heat conductivity is not constant but is an increasing monotonic function of temperature.
We study heat rectification in a minimalistic model composed of two masses subjected to on-site and coupling linear forces in contact with effective Langevin baths induced by laser interactions. Analytic expressions of the heat currents in the steady state are spelled out. Asymmetric heat transport is found in this linear system if both the bath temperatures and the temperature dependent bath-system couplings are also exchanged.
We study the dynamics of $phi^4$ kinks perturbed by an ac force, both with and without damping. We address this issue by using a collective coordinate theory, which allows us to reduce the problem to the dynamics of the kink center and width. We carry out a careful analysis of the corresponding ordinary differential equations, of Mathieu type in the undamped case, finding and characterizing the resonant frequencies and the regions of existence of resonant solutions. We verify the accuracy of our predictions by numerical simulation of the full partial differential equation, showing that the collective coordinate prediction is very accurate. Numerical simulations for the damped case establish that the strongest resonance is the one at half the frequency of the internal mode of the kink. In the conclusion we discuss on the possible relevance of our results for other systems, especially the sine-Gordon equation. We also obtain additional results regarding the equivalence between different collective coordinate methods applied to this problem.
We study conformations of the Gaussian polymer chains in d-dimensional space in the presence of an external field with the harmonic potential. We apply a path integral approach to derive an explicit expression for the probability distribution function of the gyration radius. We calculate this function using Monte Carlo simulations and show that our numerical and theoretical results are in a good agreement for different values of the external field.
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