Speaker
Description
In equilibrium statistical physics, the fluctuation-compressibility theorem states that the variance of the number of particles, in a region of space with size $R$ , scales as $σ_N∼R^d$, with d the spatial dimension. Active systems, however, often exhibit giant number fluctuations (GNF), where $σ_N∼R^d$, with $β>d$. In contrast, when $β
Recent experiments, however, using larger active nematic cells allow accessing smaller $q$. In this regime, we observe that $S(q)$ does not vanish at the lowest accessible q, but that instead it decays and saturates to a finite non-zero value. This suggests a crossover from hyperuniform to uniform behavior beyond a characteristic length scale. Uniformity suggests that at sufficiently large length scales random noise, akin to thermal effects, dominates over activity-induced fluctuations. To assess this, we compare our results with those of electric charges in equilibrium, finding that the relation between partial structure factors in this system holds for active nematic defects, thus confirming the transition from HU to uniform behavior.
