Etale cohomology, cofinite generation, and p-adic L-functions

For a prime number p and a number field k, we first study certain etale cohomology groups with coefficients associated to a p-adic Artin representation of its Galois group, where we twist the coefficients using a modified Tate twist with a p-adic index. We show that those groups are cofinitely generated and explicitly compute an additive Euler characteristic. When k is totally real and the representation is even, we relate the order of vanishing of the p-adic L-function at a point of its domain and the corank of such a cohomology group with a suitable p-adic twist. If the groups are finite, then the value of the p-adic L-function is non-zero and its p-adic absolute value is related to a multiplicative Euler characteristic. For a negative integer n (and for 0 in certain cases), this gives a proof of a conjecture by Coates and Lichtenbaum, and a short proof of the equivariant Tamagawa number conjecture for classical L-functions that do not vanish at n. For p=2 our results involving p-adic L-functions depend on a conjecture in Iwasawa theory.

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