Seat number configuration of the box-ball system, and its relation to the 10-elimination and invariant measures

Abstract

The box-ball system (BBS) is a soliton cellular automaton introduced in [TS], and it is known that the dynamics of the BBS can be linearized by several methods. Recently, a new linearization method, called the seat number configuration, was introduced in [MSSS]. In this paper, we develop this method further by introducing the $k$-skip map, which is a natural operation on the seat number configuration. From the soliton point of view, this map lowers the height of each soliton by $k$. We first show that the $k$-skip map shifts the seat number configuration and that, for finite ball configurations on the half-line, the 1-skip map coincides with the 10-elimination introduced in [MIT]. We then extend the seat number configuration and the $k$-skip map to the BBS on the whole-line. Finally, we study the distribution of the $k$-skipped configuration under the invariant measures introduced in [FG]. As an application, we compute expectations of the carriers with seat numbers, which are related to the stationary current and the effective velocity of solitons.