The Separate Universe Approach to Soft Limits
  We develop a formalism for calculating soft limits of $n$-point inflationary correlation functions using separate universe techniques. Our method naturally allows for multiple fields and leads to an elegant diagrammatic approach. As an application we focus on the trispectrum produced by inflation with multiple light fields, giving explicit formulae for all possible single- and double-soft limits. We also investigate consistency relations and present an infinite tower of inequalities between soft correlation functions which generalise the Suyama-Yamaguchi inequality. 
Zachary Kenton and David J. Mulryne
astro-ph.CO gr-qc hep-th