We explore the paradigm in which inflation is driven by a four-dimensional strongly coupled dynamics with a non-minimal coupling to gravity. We introduce a model where the inflaton is identified with the glueball field of a pure Yang-Mills theory. We introduce the dilatonic-like glueball action, which is obtained by requiring saturation of the underlying Yang-Mills trace anomaly at the effective action level. We couple the resulting action non-minimally to gravity. We demonstrate that it is possible to achieve successful inflation with the confining scale of the underlying Yang-Mills theory naturally of the order of the grand unified energy scale. We also argue that the metric formulation gives a more consistent picture for models of composite inflation than the Palatini one. Finally we show that, within the metric formulation, the model nicely respects tree-level unitarity for the scattering of the inflaton field all the way to the Planck scale.

Recent investigations have shown that inflation can be driven by four-dimensional strongly interacting theories non-minimally coupled to gravity. We explore this paradigm further by considering composite inflation driven by orientifold field theories. The advantage of using these theories resides in the fact that at large number of colors they feature certain super Yang-Mills properties. In particular we can use for inflation the bosonic part of the Veneziano-Yankielowicz effective theory. Furthermore, we include the 1/N as well as fermion mass corrections at the effective Lagrangian level allowing us to explore the effects of these corrections on the inflationary slow-roll parameters. Additionally the orientifold field theory with fermionic matter transforming according to the two-index antisymmetric representation for three colors is QCD. Therefore this model can be interpreted as a new non-minimally coupled QCD theory of inflation. The scale of composite inflation, for all the models presented here, is of the order of 10 16 GeV. Unitarity studies of the inflaton scattering suggest that the cutoff of the model is at the Planck scale.