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Running of the Spectral Index and Inflationary Dynamics of $F(R)$ Gravity

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arxiv 2206.06024 v1 pith:DDXFQJWJ submitted 2022-06-13 gr-qc astro-ph.CO

classification gr-qcastro-ph.CO
keywords indexrunningspectralmodelsgravityrangecasesfield
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abstract

In this work we shall provide a model-independent general calculation of the running of the spectral index for vacuum $F(R)$ gravities. We shall exploit the functional form of the spectral index and of the tensor-to-scalar ratio in order to present a general $n_s-r$ relation for vacuum $F(R)$ gravity theories. As we show, viable $F(R)$ gravity theories can be classified to two classes of models regarding their prediction for the running spectral index. The $R^2$-attractor models predict a running of the spectral index in the range $-10^{-3}<a_s<-10^{-4}$, which classifies them in the same universality class that most inflationary scalar field models belong to. We provide three models of this sort, for which we verify our claims in detail. However there exist viable $F(R)$ gravity models with running of spectral index outside the range $-10^{-3}<a_s<-10^{-4}$ and in some cases it can be positive. We also present an $R^2$-corrected scalar field model, which also predicts a running of the spectral index in the range $-10^{-3}<a_s<-10^{-4}$. For all the cases we studied, we found no evidence for the most phenomenologically interesting scenario of having $r<10^{-4}$ and a running $a_s<-10^{-3}$, which in principle could be realized.

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Cited by 5 Pith papers

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

  1. Non-Standard Thermal History and Formation of Primordial Black Holes in Einstein-Gauss-Bonnet Gravity

    gr-qc 2025-01 conditional novelty 5.0 of 10

    A tuned Einstein-Gauss-Bonnet inflation model can create primordial black holes from asteroid-sized to tens of solar masses and secondary gravitational waves, with abundances that change dramatically in a stiff post-i...

  2. Constraining Quintessential Inflation with ACT: A Gauss-Bonnet Gateway

    astro-ph.CO 2026-04 unverdicted novelty 4.5 of 10

    Exponential and sech Gauss–Bonnet couplings restore ACT-compatible ns and r for quintessential inflation, while tanh fails for a structural sign reason; reheating remains BBN-safe.

  3. Reconciling Fractional Power Potential and EGB Gravity in the light of ACT

    astro-ph.CO 2025-07 conditional novelty 4.0 of 10

    In EGB gravity, the V0 phi^n potential with n = 1/3 and 2/5 can produce ns and r within the 1 sigma ACT r-ns region for selected coupling values.

  4. Inflationary Dynamics of Mutated Hilltop Inflation in Einstein-Gauss-Bonnet Gravity Under New Slow-Roll Approximations with Generalised Reheating

    astro-ph.CO 2025-05 conditional novelty 4.0 of 10

    In Einstein-Gauss-Bonnet gravity, the Mutated Hilltop inflation model can satisfy Planck'18 bounds on the spectral index and tensor-to-scalar ratio when the Gauss-Bonnet coupling parameters are tuned, with the new slo...

  5. Starobinsky like inflation and EGB Gravity in the light of ACT

    astro-ph.CO 2025-05 conditional novelty 4.0 of 10

    Starobinsky inflation with a tuned Einstein-Gauss-Bonnet coupling can reproduce the ACT-enhanced scalar spectral index within 1σ.

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