Weil-étale Cohomology and Special Values of L-functions

We construct the Weil-étale cohomology and Euler characteristics for a subclass of the class of Z-constructible sheaves on an open subscheme of the spectrum of the ring of integers of a number field. Then we show that the special value of an Artin L-function of toric type at zero is given by the Weil-étale Euler characteristic of an appropriate Z-constructible sheaf up to signs. As applications of our result, we will prove a formula for the special value of the L-function of an algebraic torus at zero which is similar to Ono’s Tamagawa Number Formula.