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Beyond (and back to) Palatini quadratic gravity and inflation

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arxiv 2212.11869 v4 pith:GH4IODM3 submitted 2022-12-22 gr-qc astro-ph.COhep-ph

Christian Dioguardi , Antonio Racioppi , Eemeli Tomberg This is my paper · ORCID
classification gr-qcastro-ph.COhep-ph
keywords frameinflatonjordanpalatinipotentialbelowgravityinflation
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abstract

We study single-field slow-roll inflation embedded in Palatini $F(R)$ gravity where $F(R)$ grows faster than $R^2$. Surprisingly, the consistency of the theory requires the Jordan frame inflaton potential to be unbounded from below. Even more surprisingly, this corresponds to an Einstein frame inflaton potential bounded from below and positive definite. We prove that for all such Palatini $F(R)$'s, there exists a universal strong coupling limit corresponding to a quadratic $F(R)$ with the wrong sign for the linear term and a cosmological constant in the Jordan frame. In such a limit, the tensor-to-scalar ratio $r$ does not depend on the original inflaton potential, while the scalar spectral index $n_s$ does. Unfortunately, the system is ill-defined out of the slow-roll regime. A possible way out is to upgrade to a $F(R,X)$ model, with $X$ the Jordan frame inflaton kinetic term. Such a modification essentially leaves the inflationary predictions unaffected.

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Forward citations

Cited by 4 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score. Full citation record

  1. Inflation with Nieh-Yan-like terms in metric-affine gravity

    gr-qc 2026-08 conditional novelty 6.0 of 10

    A generalized Nieh-Yan coupling in metric-affine gravity can restore the consistency of Palatini inflation with CMB observations and produce testable tensor-to-scalar ratios.

  2. $\tilde\xi$-attractors in metric-affine gravity

    gr-qc 2024-11 conditional novelty 5.0 of 10

    A new class of metric-affine inflationary models, the ξ-tilde-attractors, reproduces Starobinsky inflation as a universal attractor in two strong-coupling limits.

  3. Constant-roll $\beta$-exponential inflation: Palatini formalism

    gr-qc 2026-01 reject novelty 4.0 of 10

    A parameter scan of constant-roll β-exponential inflation in Palatini R² gravity claims agreement with ACT/Planck contours, but the derivation is undermined by algebraic sign errors and an absent non-Gaussianity calculation.

  4. Large Field Polynomial Inflation in Palatini $f(R,\phi)$ Gravity

    astro-ph.CO 2024-11 conditional novelty 4.0 of 10

    Large-field polynomial inflation in Palatini f(R, phi) gravity can match Planck and BICEP/Keck data over broad parameter regions, and a negative R-squared coupling can suppress the tensor-to-scalar ratio to CMB-S4 levels.

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