Palatini f(R) Gravity and Variants of k-/Constant Roll/Warm Inflation within Variation of Strong Coupling Scenario

• Published in: Universe (Basel) Vol. 8; no. 2; p. 126
• Main Authors: AlHallak, Mahmoud, AlRakik, Amer, Chamoun, Nidal, El-Daher, Moustafa Sayem
• Format: Journal Article
• Language: English
• Published: Basel MDPI AG 01.02.2022
• Subjects: Energy; f(R)-gravity; Gravity; inflation; k-inflation; Kinetic energy; Theory of relativity; variation of constants
• ISSN: 2218-1997; 2218-1997
• DOI: 10.3390/universe8020126

We show that upon applying Palatini f(R), characterized by an αR2 term, within a scenario motivated by a temporal variation of strong coupling constant, then one obtains a quadratic kinetic energy. We do not drop this term, but rather study two extreme cases: α<<1 and α>>1. In both cases, one can generate a kinematically-induced inflationary paradigm. In order to fit the Planck 2018 data, the α>>1 case, called k-inflation, requires a fine tuning adjustment with nonvanishing nonminimal coupling to gravity parameter ξ, whereas the α<<1 case, studied in the constant-roll regime, can fit the data for vanishing ξ. The varying strong coupling inflation scenario remains viable when implemented through a warm inflation scenario with or without f(R) gravity.