  Using the Bond Operator Technique (BOT), we have studied the low energy
excitationspectrum of a frustrated dimerized antiferromagnetic Heisenberg
chain. In particular, we have compared our analytical results with previous
Exact Diagonalizations (ED) data. Qualitatively, the BOT results are in good
agreement with the ED data. And even a very good quantitative agreement is
obtained in some parameter region. It is clearly shown that there is only one
elementary excitation branch (lowest triplet branch) and that the two other
well defined excitations which appear below the continuum, one singlet and one
triplet, are bound states of two elementary triplets.
