Analysis of the $^{3}{\rm He}(\alpha, \gamma)^{7}{\rm Be}$ and $^{3}{\rm
  H}(\alpha,\gamma)^{7}{\rm Li}$ astrophysical direct capture reactions in a
  modified potential-model approach
  Astrophysical $S$ factors and reaction rates of the direct radiative capture
processes $^{3}{\rm He}(\alpha, \gamma)^{7}{\rm Be}$ and $^{3}{\rm
H}(\alpha,\gamma)^{7}{\rm Li}$, as well as the primordial abundance of the
$^{7}{\rm Li}$ element, are estimated in the framework of a modified two-body
potential model. It is shown that suitable modification of phase-equivalent
$\alpha-^{3}{\rm He}$ potentials in the $d$ waves can improve the description
of the astrophysical $S$ factor for the direct $^{3}{\rm He}(\alpha,
\gamma)^{7}{\rm Be}$ radiative capture reaction at energies above 0.5 MeV. An
estimated $^{7}{\rm Li/H}$ abundance ratio of $(4.89\pm 0.18 )\times 10^{-10}$
is in very good agreement with the recent measurement of $(5.0\pm 0.3) \times
10^{-10}$ by the LUNA collaboration.
