Abstract
In scalaron-Higgs inflation the Standard Model Higgs boson is non-minimally coupled to gravity and the Einstein-Hilbert action is supplemented by the quadratic scalar curvature invariant. For the quartic Higgs self-coupling λ fixed at the electroweak scale, we find that the resulting inflationary two-field model effectively reduces to a single field model with the same predictions as in Higgs inflation or Starobinsky inflation, including the limit of a vanishing non-minimal coupling. For the same model, but with the scalar field a priori not identified with the Standard Model Higgs boson, we study the inflationary consequences of an extremely small λ. Depending on the initial conditions for the inflationary background trajectories, we find that the two-field dynamics either again reduces to an effective single-field model with a larger tensor-to-scalar ratio than predicted in Higgs inflation and Starobinsky inflation, or involves the full two-field dynamics and leads to oscillatory features in the inflationary power spectrum. Finally, we investigate under which conditions the inflationary scenario with extremely small λ can be realized dynamically by the Standard Model renormalization group flow and discuss how the scalaron-Higgs model can provide a natural way to stabilize the electroweak vacuum.
Highlights
The simplest models of inflation are based on a single additional propagating scalar degree of freedom – the inflaton
Even for models belonging to the same universality class, there is still much freedom left in the theoretical description and, in many models the physical nature of the inflaton and the functional form of its potential remain unexplained at the fundamental level
For ξ 1, we find that the two valleys converge to a single broad valley located at φ = 0, which serves as the sole attractor for the model in this regime
Summary
The simplest models of inflation are based on a single additional propagating scalar degree of freedom – the inflaton. We analyze the model of scalaron-Higgs inflation, which results from a combination of Higgs inflation with a non-minimal coupling to gravity and Starobinsky’s model of inflation It is a special case of a more general f (R, φ) theory, which can be equivalently formulated as a two-field scalar-tensor theory with a curved scalar field space manifold. Depending on the initial conditions and the specific inflationary background trajectory in the landscape of the two-field potential, different scenarios are possible: if inflation takes place in one of the two valleys for λ 10−1, the model reduces to an effective single-field model different to the effective single-field model obtained for λ = 10−1 and leads to a larger tensorto-scalar ratio than predicted in non-minimal Higgs inflation or Starobinsky inflation. In terms of the variables (gμν, χ, φ) both scalar fields (χ, φ) are minimally coupled to gravity but feature a curved field space metric
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