Three-dimensional 2-critical bootstrap percolation: The stable sets approach

Consider a $p$-random subset $A$ of initially infected vertices in the discrete cube $[L{]}^3$, and assume that the neighbourhood of each vertex consists of the $a_i$ nearest neighbours in the $\pm e_i$-directions for each $i\in \{1,2,3\}$, where $a_1\le a_2\le a_3$. Suppose we infect any healthy vertex $v\in [L{]}^3$ already having $r$ infected neighbours, and that infected sites remain infected forever. In this paper we determine $\log$ of the critical length for percolation up to a constant factor, for all $r\in {a_3+1, \dots, a_3+a_2}$with$a_3\ge a_1+a_2$. We moreover give upper bounds for all remaining cases $a_3<a_1+a_2$ and believe that they are tight up to a constant factor.