Analysing Starobinsky inflation extensions in higher-order gravity
Cosmology, Inflation, Modified Gravity, High-Order Gravity, Starobinsky Model.
In 1980, the Russian physicist Alexei Starobinsky developed a cosmological model that features an accelerated expansion at the
beginning of cosmic expansion, which embraces modifications in General Relativity. Although Starobinsky's motivation was adding
corrections to remove singularities occurred with Einstein's theory, his model is one of the best-fit inflation theories regarding
observational data nowadays. Nevertheless, new data from future projects, such as the LiteBIRD satellite and the CMB-S4 experiment,
may disfavor it. Hence, extensions of it are being considered seeking shifts in parameters related to observational data. Here, three
higher-order extensions of the Starobinsky model are presented: Starobinsky + R3, Starobinsky + R☐R and Starobinsky + RRμνRμν (the last
one is a new contribution to the literature). For this, a higher-order model whose action contains up to cubic scalars (cosmological constant
not included) is developed, from which is shown that all cubic scalars relevant to inflation dynamics in background cosmology are R3,
R☐R and RRμνRμν.