  We prove the Gan-Gross-Prasad conjecture for Fourier-Jacobi periods on
unitary groups and an Ichino-Ikeda type refinement. Our strategy is based on
the comparison of relative trace formulae formulated by Liu. We develop the
full coarse spectral and geometric expansions of the relative trace formulae,
and compute relevant spectral terms via zeta integrals and truncated periods.
We compare all geometric terms and characterize the local geometric comparison
in terms of spectral data.
