  We investigate the possibility of accounting for the currently inferred
primordial abundances of D, 3He, 4He, and 7Li by big bang nucleosynthesis in
the presence of baryon density inhomogeneities plus the effects of
late-decaying massive particles (X), and we explore the allowed range of
baryonic fraction of the closure density Omega_b in such context. We find that,
depending on the parameters of this composite model (characteristic size and
density contrast of the inhomogeneities; mass-density, lifetime, and effective
baryon number in the decay of the X-particles), values as high as
\Omega_{b}h_{50}^{2}\simeq 0.25-0.35 could be compatible with the primordial
abundances of the light nuclides. We include diffusion of neutrons and protons
at all stages, and we consider the contribution of the X particles to the
energy density, the entropy production by their decay, the possibility that the
X-products could photodissociate the light nuclei produced during the previous
stages of nucleosynthesis, and also the possibility that the decay products of
the X-particles would include a substantial fraction of hadrons. Specific
predictions for the primordial abundance of Be are made.
