F-characteristic cycle of a rank one sheaf on an arithmetic surface

Abstract: We prove the rationality of the characteristic form for a degree one character of the Galois group of an abelian extension of henselian discrete valuation fields. We prove the integrality of the characteristic form for a rank one sheaf on a regular excellent scheme. These properties are shown by reducing to the corresponding properties of the refined Swan conductor proved by Kato. We define the F-characteristic cycle of a rank one sheaf on an arithmetic surface as a cycle on the FW-cotangent bundle using the characteristic form on the basis of the computation of the characteristic cycle in the equal characteristic case by Yatagawa. The rationality and the integrality of the characteristic form are necessary for the definition of the F-characteristic cycle. We prove the intersection of the F-characteristic cycle with the 0-section computes the Swan conductor of cohomology of the generic fiber.