Reconstructing the inflationary f(R) from observations

Journal Article · Fri Aug 01 04:00:00 EDT 2014 · Journal of Cosmology and Astroparticle Physics

DOI:https://doi.org/10.1088/1475-7516/2014/08/015· OSTI ID:22373413

Rinaldi, Massimiliano; Cognola, Guido; Vanzo, Luciano; Zerbini, Sergio ^[1]

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1. Dipartimento di Fisica, Università di Trento, via Sommarive 14, Trento, 38123 (Italy)

The BICEP2 collaboration has recently released data showing that the scalar-to-tensor ratio r is much larger than expected. The immediate consequence, in the context of f(R) gravity, is that the Starobinsky model of inflation is ruled out since it predicts a value of r much smaller than what is observed. Of course, the BICEP2 data need verification, especially from Planck with which there is some tension, therefore any conclusion seems premature. However, it is interesting to ask what would be the functional form of f(R) in the case when the value of r is different from the one predicted by the Starobinsky model. In this paper, we show how to determine the form of f(R), once the slow-roll parameters are known with some accuracy. The striking result is that, for given values of the scalar spectral index n{sub S} and r, the effective Lagrangian has the form f(R)=R{sup ζ}, where ζ=2-ε and |ε||| 1. Therefore, it appears that the inflationary phase of the Universe is best described by a R{sup 2} theory, with a small deviation that, as we show, can be obtained by quantum corrections.

• OSTI ID: 22373413
• Journal Information: Journal of Cosmology and Astroparticle Physics, Journal Name: Journal of Cosmology and Astroparticle Physics Journal Issue: 08 Vol. 2014; ISSN 1475-7516
• Country of Publication: United States
• Language: English

Related Subjects

79 ASTRONOMY AND ASTROPHYSICS
ACCURACY
CORRECTIONS
COSMOLOGICAL INFLATION
GRAVITATION
LAGRANGIAN FUNCTION
SCALARS
TENSORS
UNIVERSE