Motivic volumes of fibers of tropicalization.

Let T be an algebraic torus over an algebraically closed field, let X be a smooth closed subvariety of a T-toric variety such that U X BT is not empty, and let LðXÞ be the arc scheme of X. We consider a tropicalization map on LðXÞnLðXnUÞ, the set of arcs of X that do not factor through XnU. We show that each fiber of this tropicalization map is a constructible subset of LðXÞ and therefore has a motivic volume. We prove that if U has a compactification with simple normal crossing boundary, then the generating function for these motivic volumes is rational, and we express this rational function in terms of certain lattice maps constructed in Hacking, Keel, and Tevelev's theory of geometric tropicalization. We explain how this result, in particular, gives a formula for Denef and Loeser's motivic zeta function of a polynomial. To further understand this formula, we also determine precisely which lattice maps arise in the construction of geometric tropicalization. [ABSTRACT FROM AUTHOR]