Perturbative unitarity in quasi-single field inflation. (arXiv:2102.04101v2 [hep-th] UPDATED)
<a href="http://arxiv.org/find/hep-th/1/au:+Kim_S/0/1/0/all/0/1">Suro Kim</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Noumi_T/0/1/0/all/0/1">Toshifumi Noumi</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Takeuchi_K/0/1/0/all/0/1">Keito Takeuchi</a>, <a href="http://arxiv.org/find/hep-th/1/au:+Zhou_S/0/1/0/all/0/1">Siyi Zhou</a>
We study implications of perturbative unitarity for quasi-single field
inflation. Analyzing high energy scattering, we show that non-Gaussianities
with $|f_{rm NL}|gtrsim1$ cannot be realized without turning on interactions
which violate unitarity at a high energy scale. Then, we provide a relation
between $f_{rm NL}$ and the scale of new physics that is required for UV
completion. In particular we find that for the Hubble scale $Hgtrsim 6times
10^{9}$ GeV, Planck suppressed operators can easily generate too large
non-Gaussanities and so it is hard to realize successful quasi-single field
inflation without introducing a mechanism to suppress quantum gravity
corrections. Also we generalize the analysis to the regime where the
isocurvature modes are heavy and the inflationary dynamics is captured by the
inflaton effective theory. Requiring perturbative unitarity of the two-scalar
UV models with the inflaton and one heavy scalar, we clarify the parameter
space of the $P(X,phi)$ model which is UV completable by a single heavy
scalar.
We study implications of perturbative unitarity for quasi-single field
inflation. Analyzing high energy scattering, we show that non-Gaussianities
with $|f_{rm NL}|gtrsim1$ cannot be realized without turning on interactions
which violate unitarity at a high energy scale. Then, we provide a relation
between $f_{rm NL}$ and the scale of new physics that is required for UV
completion. In particular we find that for the Hubble scale $Hgtrsim 6times
10^{9}$ GeV, Planck suppressed operators can easily generate too large
non-Gaussanities and so it is hard to realize successful quasi-single field
inflation without introducing a mechanism to suppress quantum gravity
corrections. Also we generalize the analysis to the regime where the
isocurvature modes are heavy and the inflationary dynamics is captured by the
inflaton effective theory. Requiring perturbative unitarity of the two-scalar
UV models with the inflaton and one heavy scalar, we clarify the parameter
space of the $P(X,phi)$ model which is UV completable by a single heavy
scalar.
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