47 research outputs found
Finite-dimensional representation of the quadratic algebra of a generalized coagulation-decoagulation model
The steady-state of a generalized coagulation-decoagulation model on a
one-dimensional lattice with reflecting boundaries is studied using a
matrix-product approach. It is shown that the quadratic algebra of the model
has a four-dimensional representation provided that some constraints on the
microscopic reaction rates are fulfilled. The dynamics of a product shock
measure with two shock fronts, generated by the Hamiltonian of this model, is
also studied. It turns out that the shock fronts move on the lattice as two
simple random walkers which repel each other provided that the same constraints
on the microscopic reaction rates are satisfied.Comment: Minor revision
Phase transitions and correlations in the bosonic pair contact process with diffusion: Exact results
The variance of the local density of the pair contact process with diffusion
(PCPD) is investigated in a bosonic description. At the critical point of the
absorbing phase transition (where the average particle number remains constant)
it is shown that for lattice dimension d>2 the variance exhibits a phase
transition: For high enough diffusion constants, it asymptotically approaches a
finite value, while for low diffusion constants the variance diverges
exponentially in time. This behavior appears also in the density correlation
function, implying that the correlation time is negative. Yet one has dynamical
scaling with a dynamical exponent calculated to be z=2.Comment: 20 pages, 5 figure
Relaxation time in a non-conserving driven-diffusive system with parallel dynamics
We introduce a two-state non-conserving driven-diffusive system in
one-dimension under a discrete-time updating scheme. We show that the
steady-state of the system can be obtained using a matrix product approach. On
the other hand, the steady-state of the system can be expressed in terms of a
linear superposition Bernoulli shock measures with random walk dynamics. The
dynamics of a shock position is studied in detail. The spectrum of the transfer
matrix and the relaxation times to the steady-state have also been studied in
the large-system-size limit.Comment: 10 page
Ergodicity breaking in one-dimensional reaction-diffusion systems
We investigate one-dimensional driven diffusive systems where particles may
also be created and annihilated in the bulk with sufficiently small rate. In an
open geometry, i.e., coupled to particle reservoirs at the two ends, these
systems can exhibit ergodicity breaking in the thermodynamic limit. The
triggering mechanism is the random motion of a shock in an effective potential.
Based on this physical picture we provide a simple condition for the existence
of a non-ergodic phase in the phase diagram of such systems. In the
thermodynamic limit this phase exhibits two or more stationary states. However,
for finite systems transitions between these states are possible. It is shown
that the mean lifetime of such a metastable state is exponentially large in
system-size. As an example the ASEP with the A0A--AAA reaction kinetics is
analyzed in detail. We present a detailed discussion of the phase diagram of
this particular model which indeed exhibits a phase with broken ergodicity. We
measure the lifetime of the metastable states with a Monte Carlo simulation in
order to confirm our analytical findings.Comment: 25 pages, 14 figures; minor alterations, typos correcte
Ageing in bosonic particle-reaction models with long-range transport
Ageing in systems without detailed balance is studied in bosonic contact and
pair-contact processes with Levy diffusion. In the ageing regime, the dynamical
scaling of the two-time correlation function and two-time response function is
found and analysed. Exact results for non-equilibrium exponents and scaling
functions are derived. The behaviour of the fluctuation-dissipation ratio is
analysed. A passage time from the quasi-stationary regime to the ageing regime
is defined, in qualitative agreement with kinetic spherical models and p-spin
spherical glasses.Comment: Latex2e, 24 pages, with 9 figures include
Dynamics of an exclusion process with creation and annihilation
We examine the dynamical properties of an exclusion process with creation and
annihilation of particles in the framework of a phenomenological domain-wall
theory, by scaling arguments and by numerical simulation. We find that the
length- and time scale are finite in the maximum current phase for finite
creation- and annihilation rates as opposed to the algebraically decaying
correlations of the totally asymmetric simple exclusion process (TASEP).
Critical exponents of the transition to the TASEP are determined. The case
where bulk creation- and annihilation rates vanish faster than the inverse of
the system size N is also analyzed. We point out that shock localization is
possible even for rates proportional to 1/N^a, 1<a<2.Comment: 16 pages, 8 figures, typos corrected, references added, section 4
revise
The non-equilibrium phase transition of the pair-contact process with diffusion
The pair-contact process 2A->3A, 2A->0 with diffusion of individual particles
is a simple branching-annihilation processes which exhibits a phase transition
from an active into an absorbing phase with an unusual type of critical
behaviour which had not been seen before. Although the model has attracted
considerable interest during the past few years it is not yet clear how its
critical behaviour can be characterized and to what extent the diffusive
pair-contact process represents an independent universality class. Recent
research is reviewed and some standing open questions are outlined.Comment: Latexe2e, 53 pp, with IOP macros, some details adde
Microscopic structure of travelling wave solutions in a class of stochastic interacting particle systems
We obtain exact travelling wave solutions for three families of stochastic
one-dimensional nonequilibrium lattice models with open boundaries. These
solutions describe the diffusive motion and microscopic structure of (i) of
shocks in the partially asymmetric exclusion process with open boundaries, (ii)
of a lattice Fisher wave in a reaction-diffusion system, and (iii) of a domain
wall in non-equilibrium Glauber-Kawasaki dynamics with magnetization current.
For each of these systems we define a microscopic shock position and calculate
the exact hopping rates of the travelling wave in terms of the transition rates
of the microscopic model. In the steady state a reversal of the bias of the
travelling wave marks a first-order non-equilibrium phase transition, analogous
to the Zel'dovich theory of kinetics of first-order transitions. The stationary
distributions of the exclusion process with shocks can be described in
terms of -dimensional representations of matrix product states.Comment: 27 page
Exchange anisotropy and the dynamic phase transition in thin ferromagnetic Heisenberg films
Monte Carlo simulations have been performed to investigate the dependence of
the dynamic phase behavior on the bilinear exchange anisotropy of a classical
Heisenberg spin system. The system under consideration is a planar thin
ferromagnetic film with competing surface fields subject to a pulsed
oscillatory external field. The results show that the films exhibit a single
discontinuous dynamic phase transition (DPT) as a function of the anisotropy of
the bilinear exchange interaction in the Hamiltonian. Furthermore there is no
evidence of stochastic resonance (SR) associated with the DPT. These results
are in marked contrast to the continuous DPT observed in the same system as a
function of temperature and applied field strength for a fixed bilinear
exchange anisotropy.Comment: 11 pages including 3 figure pages; submitted to PR
The kinetic spherical model in a magnetic field
The long-time kinetics of the spherical model in an external magnetic field
and below the equilibrium critical temperature is studied. The solution of the
associated stochastic Langevin equation is reduced exactly to a single
non-linear Volterra equation. For a sufficiently small external field, the
kinetics of the magnetization-reversal transition from the metastable to the
ground state is compared to the ageing behaviour of coarsening systems quenched
into the low-temperature phase. For an oscillating magnetic field and below the
critical temperature, we find evidence for the absence of the
frequency-dependent dynamic phase transition, which was observed previously to
occur in Ising-like systems.Comment: 26 pages, 12 figure