Discovery-HET Seminar: Subodh Patil – University of Copenhagen

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Discovery-HET Seminar: Subodh Patil

Speaker: Subodh Patil (CERN)

Title: Correlating features in the primordial specta, or, how do we know it really was an inflaton?


CMB and matter density field observations derive from n-point correlation functions of the comoving curvature perturbation R. As far as we can tell, all observations to date are consistent with the predictions of the simplest models of single-field slow roll inflation. However, if all we have access to are observations of correlators of adiabatic perturbations, one infers limited information as to what the background was actually doing. Degeneracies and dualities are known to exist between differing backgrounds that result in the same 2-point correlators, which begs a host of operational questions: how do we know whether or not inflation really happened? What is the true nature of the inflaton? How does it embed itself in a sector that also contains the standard model?

In this talk I will review how the purported common lore `smoking gun' signatures of inflation are anything but, and demonstrate that one possible way to infer that inflation really happened would be to observe a hierarchy of correlations between the different n-point correlators of R. These correlations are a direct consequence of the effective field theory expansion of R, which non-linearly realizes the breaking of time translational invariance by slow roll. The observation of such correlations in the n-point spectra over a range of e-folds would directly confirm the nature of inflaton as an effectively single light scalar degree of freedom embedded in a theory that is UV completable, and is the consequence of transient stronger couplings of certain operators in the effective theory as inflation progresses. We discuss the prospects for observing such correlations in future LSS and 21cm observations.