Marginally Extended EFT of Inflation



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PIRSA Number: 
17110105

Abstract

Extending the EFT of Inflation by adding marginal operators in unitary gauge that can affect the equation of motion for scalar perturbations, we unravel new inflationary models in which the dispersion relations is a sixth order polynomial. In particular we focus on the healthy marginal operators that do not infiltrate ghosts into the equations of motion and allow for gravity to decouple from the Goldstone boson above some energy scale. Various scenarios can arise depending on the parameters in the original theory. In particular, one can consider scenarios in which the mode becomes tachyonic while still it is inside the horizon. More conservatively, one can consider models in which the group velocity of the propagation becomes negative. In these inflationary models, the amplitude of scalar power spectrum gets a modulation factor, which in majority of the cases is much bigger than one. We also show that these marginal operators leave the tensor perturbations intact, and hence the form of tensor power spectrum remains resilient even in the marginally extended EFT of inflation. Due to the enhancement of the scalar power spectrum, the tensor-to-scalar ratio is suppressed by a huge factor..