  Quillen's localization theorem is well known as a fundamental theorem in the
study of algebraic K-theory. In this paper, we present its arithmetic analogue
for the equivariant K-theory of arithmetic schemes, which are endowed with an
action of certain diagonalisable group scheme. This equivariant arithmetic
K-theory is defined by means of a natural extension of Burgos-Wang's simplicial
description of Beilinson's regulator map to the equivariant case. As a
byproduct of this work, we give an analytic refinement of the Riemann-Roch
theorem for higher equivariant algebraic K-theory. And as an application, we
prove a higher arithmetic concentration theorem which generalizes Thomason's
corresponding result in purely algebraic case to the context of Arakelov
geometry.
