Why do I use single-size distribution?
the maximum dust size in the disk is set by whichever of two complementary barriers is more restrictive—fragmentation or radial drift (Birnstiel et al. 2012; Cridland et al. 2017).
In the fragmentation-limited regime, dust in the disk may undergo fragmentation-limited growth, producing a top-heavy, effectively single-size spectrum, previous observations theory, and experiment consistently show that when turbulent collision speeds approach the fragmentation threshold (Brauer et al. 2008; Birnstiel et al. 2010; Drążkowska et al. 2021; Marschall & Morbidelli 2023), growth stalls at the fragmentation size. More than 80 % of the solid mass then resides in particles within a factor ≲2 of this peak size, leaving the low-mass tail dynamically negligible (Birnstiel et al. 2012; Testi et al. 2014).
In the drift-limited regime, under steady radial drift, previous modeling studies found that the Stokes number remains nearly constant when dust particles drift while their size is limited by radial drift (Ida et al. 2016; Taki et al. 2021). Although these studies adopted single-size approximation, previous studies have shown that results obtained with the single-size approximation closely match those from a full-size distribution for dust growth (Birnstiel et al. 2012; Ormel 2014), making it suitable for applications such as pebble accretion modeling (Sato et al. 2016). Hence we use a single-size approximation and treat the Stokes number as a parameter (line 174–177 in the original manuscript).