Twistor Space Structure Of One-Loop Amplitudes In Gauge Theory
  We analyze the twistor space structure of certain one-loop amplitudes in gauge theory. For some amplitudes, we find decompositions that make the twistor structure manifest; for others, we explore the twistor space structure by finding differential equations that the amplitudes obey. 
Freddy Cachazo, Peter Svrcek, Edward Witten