Alternative String Theory in Twistor Space for $N=4$ Super-Yang-Mills Theory

In this Letter, an alternative string theory in twistor space is proposed for describing perturbative $N=4$ super-Yang-Mills theory. Like the recent proposal of Witten, this string theory uses twistor worldsheet variables and has manifest spacetime superconformal invariance. However, in this proposal, tree-level super-Yang-Mills amplitudes come from open string tree amplitudes as opposed to coming from $D$-instanton contributions.