Abstract
In quasi-single field inflation there are massive fields that interact with the inflaton field. If these other fields are not much heavier than the Hubble constant during inflation (H) these interactions can lead to important consequences for the cosmological energy density perturbations. The simplest model of this type has a real scalar inflaton field that interacts with another real scalar S (with mass m). In this model there is a mixing term of the form mu overset{cdot }{pi }S , where π is the Goldstone fluctuation that is associated with the breaking of time translation invariance by the time evolution of the inflaton field during the inflationary era. In this paper we study this model in the region (μ/H)2 + (m/H)2> 9/4 and m/Hsim mathcal{O}(1) or less. For a large part of the parameter space in this region standard perturbative methods are not applicable. Using numerical and analytic methods we study how large μ/H has to be for the large μ/H effective field theory approach to be applicable.
Highlights
Its predictability [16,17,18]
Using numerical and analytic methods we study how large μ and the mass m satisfy (μ/H) has to be for the large μ/H effective field theory approach to be applicable
Since the measured amplitude of the density perturbations implies that H2/φ0 is quite small the ratio μ/H can be large in the region of parameter space where the operator expansion in powers of 1/Λ is justified
Summary
The simplest quasi-single field inflation model has a real scalar inflaton field φ that interacts with another real scalar field S. In this case the non-gaussianities are very small Another possibility is that there is physics at a scale Λ that is large compared to the Hubble constant during inflation but well below the Planck scale. Without tuning the tadpole in VS to cancel φ20S/Λ, it is not possible to have the mass parameter m of order the Hubble constant (or smaller) and μ/H large It seems worth studying this region of parameter space since there are some novel features that arise there. Since the measured amplitude of the density perturbations implies that H2/φ0 is quite small the ratio μ/H can be large in the region of parameter space where the operator expansion in powers of 1/Λ is justified. This is just a naturalness constraint and can be violated without the model being inconsistent
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