arXiv subjects

Aditi Simha

Publications and source records attributed to Aditi Simha.

6 recordsLinked to original sources

arXiv2020

Kardar-Parisi-Zhang universality in two-component driven diffusive models: Symmetry and renormalization group perspectives

We elucidate the universal spatio-temporal scaling properties of the time-dependent correlation functions in a class of two-component one-dimensional (1D) driven diffusive system that consists of two coupled asymmetric exclusion process. By using a perturbative renormalization group framework, we show that the relevant scaling exponents have values same as those for the 1D Kardar-Parisi-Zhang (KPZ) equation. We connect these universal scaling exponents with the symmetries of the model equations. We thus establish that these models belong to the 1D KPZ universality class.

cond-mat.stat-mech↗

arXiv2017

Phase separation in binary mixtures of active and passive particles

We study binary mixtures of small active and big passive athermal particles interacting via soft repulsive forces on a frictional substrate. Athermal self propelled particles are known to phase separate into a dense aggregate and a dilute gas-like phase at fairly low packing fractions. Known as {\emph {motility induced phase separation}}, this phenomenon governs the behaviour of binary mixtures for small to intermediate size ratios of the particle species. An effective attraction between passive particles, due to the surrounding active medium, leads to true phase separation for large size ratios and volume fractions of active particles. The effective interaction between active and passive particles can be attractive or repulsive at short range depending on the size ratio and volume fractions of the particles. This affects the clustering of passive particles. We find three distinct phases based on the spatial distribution of passive particles. The cluster size distribution of passive particles decays exponentially in the {\emph{homogeneous phase}}. It decays as a power law with an exponential cutoff in the {\emph{clustered phase}} and tends to a power law as the system approaches the transition to the {\emph{phase separated state}}. We present a phase diagram in the plane defined by the size ratio and volume fraction of passive particles.

cond-mat.soft↗

arXiv2017

Universal spatio-temporal scaling of distortions in a drifting lattice

We study the dynamical response to small distortions of a lattice about its uniform state, drifting through a dissipative medium due to an external force, and show, analytically and numerically, that the fluctuations, both transverse and longitudinal to the direction of the drift, exhibit spatiotemporal scaling belonging to the Kardar-Parisi-Zhang universality class. Further, we predict that a colloidal crystal drifting in a constant electric field is linearly stable against distortions and the distortions propagate as underdamped waves.

cond-mat.soft↗

arXiv2016

Large deviation statistics of non-equilibrium fluctuations in a sheared model-fluid

We analyse the statistics of the shear stress in a one dimensional \emph{model fluid}, that exhibits a rich phase behaviour akin to real complex fluids under shear. We show that the energy flux satisfies the Gallavotti-Cohen FT across all phases in the system. The theorem allows us to define an effective temperature which deviates considerably from the equilibrium temperature as the noise in the system increases. This deviation is negligible when the system size is small. The dependence of the effective temperature on the strain rate is phase-dependent. It doesn't vary much at the phase boundaries. The effective temperature can also be determined from the large deviation function of the energy flux. The local strain rate statistics obeys the large deviation principle and satisfies a fluctuation relation. It does not exhibit a distinct kink near zero strain rate because of inertia of the rotors in our system.

cond-mat.stat-mech↗

arXiv2009

Comment on `Detailed balance has a counterpart in non-equilibrium steady states'

Transition rates in continuously driven steady states were derived in [Evans R M L, 2005 J. Phys. A: Math. Gen. 38, 293] by demanding that no information other than the microscopic laws of motion and the macroscopic observables of the system be used to describe it. In addition to the mean energy at equilibrium, and unlike them, these driven states have a finite throughput of flux. This implies that the (nonequilibrium) reservoir, to which the system is weakly coupled, is fully characterised by its mean energy and mean flux. While we expect the resulting prescription for the rates in continuous and discretised time versions of models of real systems to be equivalent, it is not trivial to see this from the expression for the rates derived previously. We demonstrate this equivalence for a model of activated processes solved previously for continuous time, thus demonstrating consistency of theory.

cond-mat.stat-mech↗

arXiv2007

Properties of a non-equilibrium heat bath

At equilibrium, a fluid element, within a larger heat bath, receives random impulses from the bath. Those impulses, which induce stochastic transitions in the system (the fluid element), respect the principle of detailed balance, because the bath is also at equilibrium. Under continuous shear, the fluid element adopts a non-equilibrium steady state. Because the surrounding bath of fluid under shear is also in a non-equilibrium steady state, the system receives stochastic impulses with a non-equilibrium distribution. Those impulses no longer respect detailed balance, but are nevertheless constrained by rules. The rules in question, which are applicable to a wide sub-class of driven steady states, were recently derived [R. M. L. Evans, Phys. Rev. Lett. {\bf 92}, 150601 (2004); J. Phys. A: Math. Gen. {\bf 38}, 293 (2005)] using information-theoretic arguments. In the present paper, we provide a more fundamental derivation, based on the uncontroversial, non-Bayesian interpretation of probabilities as simple ratios of countable quantities. We apply the results to some simple models of interacting particles, to investigate the nature of forces that are mediated by a non-equilibrium noise-source such as a fluid under shear.

cond-mat.stat-mech↗