4.6 Article

Multiple soft limits of cosmological correlation functions

Journal

Publisher

IOP PUBLISHING LTD
DOI: 10.1088/1475-7516/2015/01/012

Keywords

inflation; cosmological perturbation theory; non-gaussianity; physics of the early universe

Funding

  1. NASA ATP [NNX11AI95G]
  2. NSF CAREER Award [PHY-1145525]
  3. Kavli Institute for Cosmological Physics at the University of Chicago [NSF PHY-1125897]
  4. Robert R. McCormick Postdoctoral Fellowship
  5. Direct For Mathematical & Physical Scien
  6. Division Of Physics [1145525, 1125897] Funding Source: National Science Foundation

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We derive novel identities satisfied by inflationary correlation functions in the limit where two external momenta are taken to be small. We derive these statements in two ways: using background-wave arguments and as Ward identities following from the fixed-time path integral. Interestingly, these identities allow us to constrain some of the O(q(2)) components of the soft limit, in contrast to their single-soft analogues. We provide several nontrivial checks of our identities both in the context of resonant non-Gaussianities and in small sound speed models. Additionally, we extend the relation at lowest order in external momenta to arbitrarily many soft legs, and comment on the many-soft extension at higher orders in the soft momentum. Finally, we consider how higher soft limits lead to identities satisfied by correlation functions in large-scale structure.

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