Brownian particles suspended in disordered crowded environments often exhibit non-Gaussian normal diffusion (NGND), whereby their displacements grow with mean square proportional to the observation time and non-Gaussian statistics. Their distributions appear to decay almost exponentially according to “universal” laws largely insensitive to the observation time. This effect is generically attributed to slow environmental fluctuations, which perturb the local configuration of the suspension medium. To investigate the microscopic mechanisms responsible for the NGND phenomenon, we study Brownian diffusion in low dimensional systems, like the free diffusion of ellipsoidal and active particles, the diffusion of colloidal particles in fluctuating corrugated channels and Brownian motion in arrays of planar convective rolls. NGND appears to be a transient effect related to the time modulation of the instantaneous particle’s diffusivity, which can occur even under equilibrium conditions. Consequently, we propose to generalize the definition of NGND to include transient displacement distributions which vary continuously with the observation time. To this purpose, we provide a heuristic one-parameter function, which fits all time-dependent transient displacement distributions corresponding to the same diffusion constant. Moreover, we reveal the existence of low dimensional systems where the NGND distributions are not leptokurtic (fat exponential tails), as often reported in the literature, but platykurtic (thin sub-Gaussian tails), i.e., with negative excess kurtosis. The actual nature of the NGND transients is related to the specific microscopic dynamics of the diffusing particle.

悬浮在无序拥挤环境中的布朗粒子通常表现出非高斯正态扩散（NGND），因此它们的位移以与观察时间和非高斯统计量成正比的均方根增长。根据对观测时间不敏感的“普遍”定律，它们的分布似乎呈指数衰减。这种影响通常归因于缓慢的环境波动，这会扰动悬浮介质的局部配置。为了研究造成NGND现象的微观机制，我们研究了低维系统中的布朗扩散，例如椭圆形和活性粒子的自由扩散，波动波纹通道中胶体粒子的扩散以及平面对流辊阵列中的布朗运动。NGND似乎是与瞬时粒子扩散率的时间调制相关的瞬态效应，即使在平衡条件下也可能发生。因此，我们建议对NGND的定义进行概括，以包括随观察时间连续变化的瞬态位移分布。为此，我们提供了一种启发式一参数函数，该函数适合与相同扩散常数相对应的所有与时间有关的瞬态位移分布。此外，我们揭示了低维系统的存在，其中NGND分布不是像文献中经常报道的那样是轻快的（胖指数尾巴），而是平直的（稀疏的高斯尾巴），即负峰度。