Igusa zeta function

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In mathematics, an Igusa zeta function is a type of generating function, counting the number of solutions of an equation, modulop, p2, p3, and so on.

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Definition

For a prime number p let K be a p-adic field, i.e. , R the valuation ring and P the maximal ideal. For we denote by the valuation of z, , and for a uniformizing parameter π of R.

Furthermore let be a Schwartz–Bruhat function, i.e. a locally constant function with compact support and let be a character of .

In this situation one associates to a non-constant polynomial the Igusa zeta function

where and dx is Haar measure so normalized that has measure 1.

Igusa's theorem

Jun-IchiIgusa  ( 1974 ) showed that is a rational function in . The proof uses Heisuke Hironaka's theorem about the resolution of singularities. Later, an entirely different proof was given by Jan Denef using p-adic cell decomposition. Little is known, however, about explicit formulas. (There are some results about Igusa zeta functions of Fermat varieties.)

Congruences modulo powers of P

Henceforth we take to be the characteristic function of and to be the trivial character. Let denote the number of solutions of the congruence

.

Then the Igusa zeta function

is closely related to the Poincaré series

by

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