$A+ A \to \emptyset$ system in one dimension with particle motion determined by nearest neighbour distances: results for parallel updates

Abstract: A one dimensional $A+A \to \emptyset$ system where the direction of motion of the particles is determined by the position of the nearest neighours is studied. The particles move with a probability $0.5 + \epsi$ towards their nearest neighbours with $-0.5 \leq \epsi \leq 0.5$. This implies a stochastic motion towards the nearest neighbour or away from it for positive and negative values of $\epsi$ respectively, with $\epsi = \pm ~0.5$ the two deterministic limits. The position of the particles are updated in parallel. The macroscopic as well as tagged particle dynamics are studied which show drastic changes from the diffusive case $\epsi=0$. The decay of particle density shows departure from the usual power law behaviour as found in $\epsi =0$, on both sides of $\epsi =0$ and a scaling regime is obtained for $\epsi > 0$. The $\epsi =0.5$ point is characterized by the presence of dimers, which are isolated pairs of particles in adjacent sites that are never annihilated. The persistence probability is also calculated that decays in a stretched exponential manner for $\epsi < 0$ and switches over to power law behaviour for $\epsi \geq 0$, with different exponents for $\epsi =0$ and $\epsi > 0$. For the tagged particle, the probability distribution $\Pi(x,t)$ that it is at position $x$ at time $t$ shows the existence of a scaling variable $x/t^\nu$ where $\nu = 0.55 \pm 0.05$ for $\epsi > 0$ and varies with $\epsi$ for $\epsi < 0$. Finally, a comparative analysis for the behaviour of all the relevant quantities for the system using parallel and asynchronous dynamics (studied recently) shows that there are significant differences for $\epsi > 0$ while the results are qualitatively similar for $\epsi < 0$.