Beyond Einstein’s General Relativity: Hybrid Metric-Palatini Gravity

Abstract

It has been established that both metric and Palatini versions of f (R) gravity have interesting features, but also manifest several downsides. A hybrid combination of theories, containing elements from both formalisms, turns out to be very successful in accounting for the observed phenomenology and it is able to avoid some drawbacks of the original approaches. Here, we explore the formulation in a dynamically equivalent scalar-tensor form of this hybrid metricPalatini approach. We present several of its main achievements, such as, passing the Solar System observational tests even if the scalar field is very light or massless, and outline several applications to astrophysical and cosmological scenarios. Furthermore, we also explore the viability of generalized hybrid metric-Palatini gravitational theories.