Jared Kaplan, IAS
The Effective Field Theory of Inflation
October 24, 2007

We study the effective field theory of inflation, i.e. the most
general theory describing the fluctuations around a quasi de Sitter
background, in the case of single field models. The scalar mode can be
eaten by the metric by going to unitary gauge. In this gauge, the most
general theory is built with the lowest dimension operators invariant
under spatial diffeomorphisms, like g^{00} and K_{mu nu}, the extrinsic
curvature of constant time surfaces. This approach allows us to
characterize all the possible high energy corrections to simple slow-roll
inflation, whose sizes are constrained by experiments. Also, it describes
in a common language all single field models, including those with a small
speed of sound and Ghost Inflation, and it makes explicit the implications
of having a quasi de Sitter background. The non-linear realization of time
diffeomorphisms forces correlation among different observables, like a
reduced speed of sound and an enhanced level of non-Gaussianity.