  We study special cycles on integral models of Shimura varieties associated
with unitary similitude groups of signature (n-1,1). We construct an arithmetic
theta lift from harmonic Maass forms of weight 2-n to the arithmetic Chow group
of the integral model of a unitary Shimura variety, by associating to a
harmonic Maass form f a linear combination of Kudla-Rapoport divisors, equipped
with the Green function given by the regularized theta lift of f.
  Our main result is an equality of two complex numbers: (1) the height pairing
of the arithmetic theta lift of f against a CM cycle, and (2) the central
derivative of the convolution L-function of a weight n cusp form (depending on
f) and the theta function of a positive definite hermitian lattice of rank n-1.
When specialized to the case n=2, this result can be viewed as a variant of the
Gross-Zagier formula for Shimura curves associated to unitary groups of
signature (1,1). The proof relies on, among other things, a new method for
computing improper arithmetic intersections.
