The ground state of the S=1/2 Heisenberg antiferromagnet on the pyrochlore
lattice is theoretically investigated. Starting from the limit of isolated
tetrahedra, I include interactions between the tetrahedra and obtain an
effective model for the spin-singlet ground state multiplet by third-order
perturbation. I determine its ground state using the mean-field approximation
and found a dimerized state with a four-sublattice structure, which agrees with
the proposal by Harris et al. I also discuss chirality correlations and spin
correlations for this state.Comment: 4 pages in 2-column format, 5 figures; To appear in J. Phys. Soc.
Jpn. (Mar, 2001