String-Inspired Infinite-Derivative Theories of Gravity: A Brief   Overview
  In String Theory there often appears a rather interesting class of higher derivative theories containing an infinite set of derivatives in the form of an exponential. These theories may provide a way to tame ultraviolet divergences without introducing ghost-like states. In this invited article we provide a brief overview on the progress that has been made over the last decade to construct such infinite derivative theories of gravity which may be able to address the singularity problems in gravity. In the process we will also be able to present some general results that applies to covariant torsion-free metric theories of gravity. 
Tirthabir Biswas, Spyridon Talaganis
gr-qc astro-ph.CO hep-th