Abstract
Higgs G-inflation is an inflation model that takes advantage of a Galileon-like derivative coupling. It is a non-renormalizable operator and is strongly coupled at high energy scales. Perturbative analysis does not have a predictive power any longer there. In general, when the Lagrangian is expanded around the vacuum, the strong coupling scale is identified as the mass scale that appears in non-renormalizable operators. In inflationary models, however, the identification of the strong coupling scale is subtle, since the structures of the kinetic term as well as the interaction itself can be modified by the background inflationary dynamics. Therefore, the strong coupling scale depends on the background. In this letter, we evaluate the strong coupling scale of the fluctuations around the background in the Higgs G-inflation including the Nambu–Goldstone modes associated with the symmetry breaking. We find that the system is sufficiently weakly coupled when the scales which we now observe exit the horizon during inflation and the observational predictions with the semiclassical treatment are valid. However, we also find that the inflaton field value at which the strong coupling scale and the Hubble scale meet is less than the Planck scale. Therefore, we cannot describe the model from the Planck scale, or the chaotic initial condition.
Highlights
The identification of inflaton is one of the remaining key pieces in the inflationary cosmology
Since the Higgs field is its unique candidate in the standard model (SM), investigating the possibilities of inflation driven by the SM Higgs field is one of the important issues for both high energy physics and cosmology
Among many proposals of the Higgs inflation models [1,2,3], Higgs G-inflation [4], where the kinetic term of the Higgs field is dominated by a Galileon-like term [5,6,7,8] during inflation, has a distinct characteristic
Summary
The identification of inflaton is one of the remaining key pieces in the inflationary cosmology. Among many proposals of the Higgs inflation models [1,2,3], Higgs G-inflation [4], where the kinetic term of the Higgs field is dominated by a Galileon-like term [5,6,7,8] during inflation, has a distinct characteristic It can generate a large gravitational wave background, violating the (standard) Lyth bound [10, 11]. Since the Higgs field value itself during inflation is larger than the strong coupling scale, it would be impossible to connect the results of the low-energy collider experiments to the precise values of running couplings at the inflationary scale without the knowledge of the UV physics behind the model, as is the case of the Higgs inflation with non-minimal coupling to gravity [13, 17, 18]
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