Université de GenèveDépartement de Physique ThéoriqueCAP Genève

Operator Product Expansion of Inflationary Correlators and Conformal Symmetry of de Sitter

7. May 2012
Cite as: 
A. Kehagias and A. Riotto [arXiv:1205.1523]
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We study the multield inflationary models where the cosmological perturbation is sourced by light scalar fields other than the inflaton. The corresponding perturbations are both scale invariant and special conformally invariant. We exploit the operator product expansion technique of conformal eld theories to study the  inflationary correlators enjoying the symmetries present during the de Sitter epoch. The operator product expansion is particularly powerful in characterizing in infationary correlation functions in two observationally interesting limits, the squeezed limit of the three-point correlator and the collapsed limit of the four-point correlator. Despite the fact that the shape of the four-point correlators is not fixed by the symmetries of de Sitter, its exact shape can be found in the collapsed limit making use of the operator product expansion. By employing the fact that conformal invariance imposes the two-point cross-correlations of the light elds to vanish unless the elds have the same conformal weights, we are able to show that the Suyama-Yamaguchi inequality relating the coecients fNL of the bispectrum in the squeezed limit and τNL of the trispectrum in the collapsed limit also holds when the light elds are intrinsically non-Gaussian. In fact, we show that the inequality is valid irrespectively of the conformal symmetry, being just a consequence of fundamental physical principles, such as the short-distance expansion of operator products. The observation of a strong violation of the inequality will then have profound implications for  inflationary models as it will imply either that multifield inflation cannot be responsible for generating the observed  fluctuations independently of the details of the model or that some new non-trivial degrees of freedom play a role during in inflation.


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