Latest Papers in Condensed Matter Physics

Statistical Mechanics

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Fixation Probabilities in Weakly Compressible Fluid Flows (1808.07128v2)

Abigail Plummer, Roberto Benzi, David R. Nelson, Federico Toschi

2018-08-21

Competition between biological species in marine environments is affected by the motion of the surrounding fluid. An effective 2D compressibility can arise, for example, from the convergence and divergence of water masses at the depth at which passively traveling photosynthetic organisms are restricted to live. In this report, we seek to quantitatively study genetics under flow. To this end, we couple an off-lattice agent-based simulation of two populations in 1D to a weakly compressible velocity field--first a sine wave and then a shell model of turbulence. We find for both cases that even in a regime where the overall population structure is approximately unaltered, the flow can significantly diminish the effect of a selective advantage on fixation probabilities. We understand this effect in terms of the enhanced survival of organisms born at sources in the flow and the influence of Fisher genetic waves.

Critical slowing down and entanglement protection (1901.07985v1)

Eliana Fiorelli, Alessandro Cuccoli, Paola Verrucchi

2019-01-23

We consider a quantum device interacting with a quantum many-body environment which features a second-order phase transition at . Exploiting the description of the critical slowing down undergone by according to the Kibble-Zurek mechanism, we explore the possibility to freeze the environment in a configuration such that its impact on the device is significantly reduced. Within this framework, we focus upon the magnetic-domain formation typical of the critical behaviour in spin models, and propose a strategy that allows one to protect the entanglement between different components of from the detrimental effects of the environment.

Bacterial range expansions on a growing front: Roughness, Fixation, and Directed Percolation (1901.07956v1)

Jordan M. Horowitz, Mehran Kardar

2019-01-23

Directed Percolation (DP) is a classic model for nonequilibrium phase transitions into a single absorbing state (fixation). It has been extensively studied by analytical and numerical techniques in diverse contexts. Recently, DP has appeared as a generic model for the evolutionary/ecological dynamics of competing bacterial populations. Range expansion -- the stochastic reproduction of bacteria competing for space to be occupied by their progeny -- leads to a fluctuating and rough growth front, which is known from experiment and simulation to affect the underlying critical behavior of the DP transition. In this work, we employ symmetry arguments to construct a pair of non-linear stochastic partial differential equations describing the co-evolution of surface roughness with the composition field of DP. Macroscopic manifestations (phenomenology) of these equations on growth patterns and genealogical tracks of range expansion are discussed; followed by a renormalization group analysis of possible scaling behaviors at the DP transition.

Self-avoiding walks and connective constants in clustered scale-free networks (1901.07948v1)

Carlos P. Herrero

2019-01-23

Various types of walks on complex networks have been used in recent years to model search and navigation in several kinds of systems, with particular emphasis on random walks. This gives valuable information on network properties, but self-avoiding walks (SAWs) may be more suitable than unrestricted random walks to study long-distance characteristics of complex systems. Here we study SAWs in clustered scale-free networks, characterized by a degree distribution of the form for large . Clustering is introduced in these networks by inserting three-node loops (triangles). The long-distance behavior of SAWs gives us information on asymptotic characteristics of such networks. The number of self-avoiding walks, , has been obtained by direct enumeration, allowing us to determine the {\em connective constant} of these networks as the large- limit of the ratio . An analytical approach is presented to account for the results derived from walk enumeration, and both methods give results agreeing with each other. In general, the average number of SAWs is larger for clustered networks than for unclustered ones with the same degree distribution. The asymptotic limit of the connective constant for large system size depends on the exponent of the degree distribution: For , converges to a finite value as ; for , the size-dependent diverges as , and for we have .

Tangled Worldview Model of Opinion Dynamics (1901.06372v2)

Hardik Rajpal, Fernando Rosas, Henrik Jeldtoft Jensen

2019-01-18

We study the joint evolution of worldviews by proposing a model of opinion dynamics, which is inspired in notions from evolutionary ecology. Agents update their opinion on a specific issue based on their propensity to change -- asserted by the social neighbours -- weighted by their mutual similarity on other issues. Agents are, therefore, more influenced by neighbours with similar worldviews (set of opinions on various issues), resulting in a complex co-evolution of each opinion. Simulations show that the worldview evolution exhibits events of intermittent polarization when the social network is scale-free. This, in turn, trigger extreme crashes and surges in the popularity of various opinions. Using the proposed model, we highlight the role of network structure, bounded rationality of agents, and the role of key influential agents in causing polarization and intermittent reformation of worldviews on scale-free networks.

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