  The virtual photon theory (VPT), which is based on first-order Coulomb
dissociation restricted to the electric dipole ($E1$), has been successfully
used to explain the breakup data for several cases. Our aim is to study the
role of various higher-order processes that are ignored in the VPT, such as the
nuclear breakup, interference between nuclear and Coulomb amplitudes, and
multistep breakup processes mainly due to strong continuum-continuum couplings
in the breakup of two-body projectiles on a heavy target at both intermediate
and higher incident energies. For the purpose of numerical calculations, we
employed eikonal version of three-body continuum-discretized coupled-channels
(CDCC) reaction model. Our results for the breakup of $^{11}$Be and $^{17}$F on
$^{208}$Pb target at 100, 250, and 520 MeV/A, show the importance of nuclear
breakup contribution, and its significant role in the multistep processes. The
multistep effect on Coulomb breakup for core-neutron projectile was found to be
negligible, whereas it was important for core-proton projectile.
Coulomb-nuclear interference (CNI) effect was also found to be non-negligible.
Quantitatively, the multistep effects due to the nuclear breakup was found to
depend on the incident energy through the energy dependence of the core-target
and nucleon-target nuclear potentials. The nuclear breakup component, the CNI
effect, and the multistep breakup processes are all found to be non-negligible;
hence, the assumptions adopted in the VPT for the accurate description of
breakup cross sections are not valid.
