# The eternal multiplicative coalescent encoding via excursions of L\'evy-type processes, with Supplement

## TL;DR

This paper provides a comprehensive encoding of the eternal multiplicative coalescent process using excursions of Lévy-type processes, resolving an open problem and clarifying the relationship between process time and Lévy process drift.

## Contribution

It establishes that each eternal version of the multiplicative coalescent is fully encoded by its Lévy-type process, confirming the process time corresponds to the linear drift increase.

## Key findings

- Eternal multiplicative coalescent is encoded by Lévy-type excursions.
- Process time matches linear drift increase in Lévy process.
- Resolves an open problem from Aldous (1997).

## Abstract

The multiplicative coalescent is a mean-field Markov process in which any pair of blocks coalesces at rate proportional to the product of their masses. In Aldous and Limic (1998) each extreme eternal version of the multiplicative coalescent was described in three different ways, one of which matched its (marginal) law to that of the ordered excursion lengths above past minima of a certain L\'evy-type process. Using a modification of the breadth-first-walk construction from Aldous (1997) and Aldous and Limic (1998), and some new insight from the thesis by Uribe (2007), this work settles an open problem (3) from Aldous (1997) in the more general context of Aldous and Limic (1998). Informally speaking, each eternal version is entirely encoded by its L\'evy-type process, and contrary to Aldous' original intuition, the time for the multiplicative coalescent does correspond to the linear increase in the constant part of the drift of the L\'e}y-type process. In the "standard multiplicative coalescent" context of Aldous (1997), this result was first announced by Armend\'ariz in 2001, while its first published proof is due to Broutin and Marckert (2016), who simultaneously account for the process of excess (or surplus) edge counts.