**The Cosmological Phonon: Symmetries on Sub-Horizon Scales**

Curvature perturbations during inflation, which seed anisotropies in the CMB, can be described as phonons propagating on the inflationary background. Indeed the spacetime expansion breaks spontaneously time diffeomorphisms and Lorentz boost invariance generating such phonon-like behaviour. This representation is at the heart of the construction of the Effective Field Theory (EFT) of inflation. In this talk I will present an algebraic classification of the possible symmetries of a shift-symmetric scalar that is assumed to non-linearly realise Lorentz boosts. Such theories include for instance scalar modes in the EFT of inflation on sub-horizon scales, superfluid or galileid phonons (the broken phase of Galileon scalar EFTs). In direct analogy with previous classifications of so-called exceptional (Lorentz invariant) EFTs we will discover theories which are characterised by a single coupling constant such as a new galileid theory, “the extended galileid”. I will also discuss symmetries of the broken phase of the Dirac-Born-Infeld scalar and their signature in primordial Non-Gaussianity.

Host: Kurt Hinterbichler

Zoom meeting ID: 999 3023 4812

For the password to access the meeting please contact one of us:

Kurt Hinterbichler: kjh92

Kara Farnsworth: kmf137

Ellen Rabe: exr223

Idit Zehavi: ixz6

at case.edu