Let F be a Hermitian vector
bundle on an arithmetic variety X over ℤ. We prove an inequality between the
L2-norm of an element in H1(X,F∨) and arithmetic Chern classes of F
under certain stability condition. This is a higher dimensional analogue of a
result of C. Soulé for Hermitian line bundles on arithmetic surfaces. We
observe that our result is related to a conjectural inequality of Miyaoka-Yau
type.