Width and extremal height distributions of fluctuating interfaces with window boundary conditions

We present a detailed study of squared local roughness (SLRDs) and local extremal height distributions (LEHDs), calculated in windows of lateral size $l$, for interfaces in several universality classes, in substrate dimensions $d_s = 1$ and $d_s = 2$. We show that their cumulants follow a Family-Vicsek type scaling, and, at early times, when $xi ll l$ ($xi$ is the correlation length), the rescaled SLRDs are given by log-normal distributions, with their $n$th cumulant scaling as $(xi/l)^{(n-1)d_s}$. This give rise to an interesting temporal scaling for such cumulants $leftlangle w_n rightrangle_c sim t^{gamma_n}$, with $gamma_n = 2 n beta + {(n-1)d_s}/{z} = left[ 2 n + {(n-1)d_s}/{alpha} right] beta$. This scaling is analytically proved for the Edwards-Wilkinson (EW) and Random Deposition interfaces, and numerically confirmed for other classes. In general, it is featured by small corrections and, thus, it yields exponents $gamma_n$s (and, consequently, $alpha$, $beta$ and $z$) in nice agreement with their respective universality class. Thus, it is an useful framework for numerical and experimental investigations, where it is, usually, hard to estimate the dynamic $z$ and mainly the (global) roughness $alpha$ exponents. The stationary (for $xi gg l$) SLRDs and LEHDs of Kardar-Parisi-Zhang (KPZ) class are also investigated and, for some models, strong finite-size corrections are found. However, we demonstrate that good evidences of their universality can be obtained through successive extrapolations of their cumulant ratios for long times and large $l$s. We also show that SLRDs and LEHDs are the same for flat and curved KPZ interfaces.