Arithmetic intersection theory on flag varieties

Abstract

Let F be the complete flag variety over Spec(Z) with the tautological filtration 0 \subset E_1 \subset E_2 \subset ... \subset E_n=E of the trivial bundle E over F. The trivial hermitian metric on E(\C) induces metrics on the quotient line bundles L_i(\C). Let \hat{c}_1(L_i) be the first Chern class of L_i in the arithmetic Chow ring \hat{CH}(F) and x_i = -\hat{c}_1(L_i). Let h(X_1,...,X_n) be a polynomial with integral coefficients in the ideal generated by the elementary symmetric polynomials e_i. We give an effective algorithm for computing the arithmetic intersection h(x_1,...,x_n) in \hat{CH}(F), as the class of a SU(n)-invariant differential form on F(\C). In particular we show that all the arithmetic Chern numbers one obtains are rational numbers. The results are true for partial flag varieties and generalize those of Maillot for grassmannians. An `arithmetic Schubert calculus' is established for an `invariant arithmetic Chow ring' which specializes to the Arakelov Chow ring in the grassmannian case.