Minimal Higgs inflation with an R 2 term in Palatini gravity

2020

Gen Relativ Gravit

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We present an introduction to cosmic inflation in the context of Palatini gravity, which is an interesting alternative to the usual metric theory of gravity. In the latter case only the metric g µν determines the geometry of space-time, whereas in the former case both the metric and the space-time connection Γ λ µν are a priori independent variables -a choice which can lead to a theory of gravity different from the metric one. In scenarios where the field(s) responsible for cosmic inflation are coupled non-minimally to gravity or the gravitational sector is otherwise extended, assumptions of the underlying gravitational degrees of freedom can have a big impact on the observational consequences of inflation. We demonstrate this explicitly by reviewing several interesting and well-motivated scenarios including Higgs inflation, R 2 inflation, and ξ-attractor models. We also discuss some prospects for future research and argue why r = 10 −3 is a particularly important goal for future missions that search for signatures of primordial gravitational waves.

Section: Cosmic Inflationmentioning

confidence: 99%

“…[93] for a recent review on metric Higgs inflation and Refs. [14,22,30,32,36,39,42,43,46,47,53] for recent studies on Palatini-Higgs inflation. The model is specified by…”

Section: Higgs Inflationmentioning

confidence: 99%

Tracing the high energy theory of gravity: an introduction to Palatini inflation

2020

Gen Relativ Gravit

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“…[2,[50][51][52][53][54][55][56][57][58][59][60][61]) and α = 0 to the scenario studied in Refs. [32,33,38,42,46,47], while α = 0 = ξ represents the minimally coupled case where only the form of V (φ) is important.…”

Section: Cosmic Inflationmentioning

confidence: 99%

Initial conditions for plateau inflation: a case study

J. Cosmol. Astropart. Phys.

Tomberg

2020

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We study initial conditions for inflation in scenarios where the inflaton potential has a plateau shape. Such models are those most favored by Planck data and can be obtained in a large number of model classes. As a representative example, we consider Higgs inflation with and without an R 2 term in the context of Palatini gravity. We show that inflation with a large number of e-folds generically occurs in a large part of the parameter space without any fine-tuning of parameters even when the scale of inflation and the inflaton field value during inflation are much smaller than the Planck scale. We discuss consequences for detection of primordial gravitational waves and spectral tilt of curvature perturbations, as well as the recently proposed "Trans-Planckian Censorship" conjecture.

“…Other models in which the tensor-to-scalar ratio can be drastically suppressed consist of Natural inflation [181][182][183] in the regime of warm inflation scenario [184], i.e. the so-called Natural Warm Inflation scenario [185][186][187], or models where the gravity sector includes also a Starobinsky-type R 2 term in the Palatini formulation [70,71,75,78]. It may also be possible to suppress the tensor-to-scalar ratio by incorporating quantum corrections to a given inflationary model.…”

Section: Discussionmentioning

confidence: 99%

Axion dark matter from Higgs inflation with an intermediate H_*

J. Cosmol. Astropart. Phys.

Visinelli

2019

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In order to accommodate the QCD axion as the dark matter (DM) in a model in which the Peccei-Quinn (PQ) symmetry is broken before the end of inflation, a relatively low scale of inflation has to be invoked in order to avoid bounds from DM isocurvature fluctuations, H * O(10 9 ) GeV. We construct a simple model in which the Standard Model Higgs field is non-minimally coupled to Palatini gravity and acts as the inflaton, leading to a scale of inflation H * ∼ 10 8 GeV. When the energy scale at which the PQ symmetry breaks is much larger than the scale of inflation, we find that in this scenario the required axion mass for which the axion constitutes all DM is m 0 0.05 µeV for a quartic Higgs self-coupling λ φ = 0.1, which correspond to the PQ breaking scale v σ 10 14 GeV and tensor-to-scalar ratio r ∼ 10 −12 . Future experiments sensitive to the relevant QCD axion mass scale can therefore shed light on the physics of the Universe before the end of inflation.