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Model-Independent Signatures of New Physics in Slow-Roll Inflation

We compute the universal generic corrections to the power spectrum in slow-roll inflation due to unknown high-energy physics. We arrive at this result via a careful integrating out of massive fields in the "in-in" formalism yielding a consistent and predictive low-energy effective description in time-dependent backgrounds. The density power spectrum is universally modified at leading order in $H/M$, the ratio of the scale of inflation to the scale of new physics; the tensor power spectrum receives only subleading corrections. In doing so, we show how to make sense of a physical momentum-cut-off in loop integrals despite dynamical redshifts, and how the result can be captured in a combined effective action/effective density matrix, where the latter contains non-adiabatic terms which modify the boundary conditions.