Are there really conformal frames? Uniqueness of affine inflation

J. Cosmol. Astropart. Phys.

2019

We study models of inflation where the scalar field φ that drives inflation is coupled non-minimally to gravity via ξφ 2 R, or where the gravity sector is enlarged by an R 2 term. We consider the original Higgs inflation, Starobinsky inflation, and two different versions of a scenario where the inflaton is a scalar field other than the Higgs, and discuss if they can be distinguished from each other by measuring the tensor-to-scalar ratio and runnings of the spectral index of primordial curvature perturbations, on top of the amplitude and spectral index of the perturbations. We consider both metric and Palatini theories of gravity, showing how detailed studies of non-minimally coupled models can help to identify the inflaton field and how they may provide for a way to also distinguish between different theories of gravity in the present context.1 As we will see, this does not necessarily amount to adding new degrees of freedom to the theory.

Section: )mentioning

confidence: 97%

Towards distinguishing variants of non-minimal inflation

Takahashi

J. Cosmol. Astropart. Phys.

2019

“…This reflects the fact that this kind of Palatini theories are metric-affine, i.e. nothing but metric theories in disguise [21,29,36,41,55,[68][69][70][71].…”

Section: Cosmic Inflationmentioning

confidence: 99%

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

2020

Gen Relativ Gravit

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.

“…This was originally noted in Ref. [4] and has recently gained increasing attention [10,11,[13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29] (see also [30][31][32]). Interestingly, it was recently pointed out in Ref.…”

Section: Introductionmentioning

confidence: 98%

Minimal Higgs inflation with an R2 term in Palatini gravity

2019

Phys. Rev. D

It has recently been suggested that the Standard Model Higgs boson could act as the inflaton while minimally coupled to gravity -given that the gravity sector is extended with an αR 2 term and the underlying theory of gravity is of Palatini, rather than metric, type. In this paper, we revisit the idea and correct some shortcomings in earlier studies. We find that in this setup the Higgs can indeed act as the inflaton and that the tree-level predictions of the model for the spectral index and the tensor-to-scalar ratio are ns 0.941, r 0.3/(1 + 10 −8 α), respectively, for a typical number of e-folds, N = 50, between horizon exit of the pivot scale k = 0.05 Mpc −1 and the end of inflation. Even though the tensor-to-scalar ratio is suppressed compared to the usual minimally coupled case and can be made compatible with data for large enough α, the result for ns is in severe tension with the Planck results. We briefly discuss extensions of the model.