Tracing the high energy theory of gravity: an introduction to Palatini inflation
Abstract
We present an introduction to cosmic inflation in the context of Palatini gravity, which is an interesting alternative to the usual metric theory of gravity. In the latter case only the metric g_{μ ν} determines the geometry of spacetime, whereas in the former case both the metric and the spacetime connection Γ_{μ}^{ν λ} are a priori independent variables—a choice which can lead to a theory of gravity different from the metric one. In scenarios where the field(s) responsible for cosmic inflation are coupled nonminimally to gravity or the gravitational sector is otherwise extended, assumptions of the underlying gravitational degrees of freedom can have a big impact on the observational consequences of inflation. We demonstrate this explicitly by reviewing several interesting and wellmotivated scenarios including Higgs inflation, R^{2} inflation, and ξ attractor models. We also discuss some prospects for future research and argue why r =10^{3} is a particularly important goal for future missions that search for signatures of primordial gravitational waves.
 Publication:

General Relativity and Gravitation
 Pub Date:
 April 2020
 DOI:
 10.1007/s10714020026822
 arXiv:
 arXiv:2001.10135
 Bibcode:
 2020GReGr..52...33T
 Keywords:

 Inflation;
 Palatini gravity;
 Metricaffine theory;
 Higgs inflation;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 General Relativity and Quantum Cosmology;
 High Energy Physics  Phenomenology
 EPrint:
 24 pages, no figures. Matches the version published in General Relativity and Gravitation