  Recent study has shown that a non-singular oscillating potential, a feature
of Infinite Derivative Gravity (IDG) theories, matches current experimental
data better than the standard GR potential. In this work we show that this
non-singular oscillating potential can be given by a wider class of theories
which allows the defocusing of null rays, and therefore geodesic completeness.
We consolidate the conditions whereby null geodesic congruences may be made
past-complete, via the Raychaudhuri Equation, with the requirement of a
non-singular Newtonian potential in an IDG theory. In so doing, we examine a
class of Newtonian potentials characterised by an additional degree of freedom
in the scalar propagator, which returns the familiar potential of General
Relativity at large distances.
