Cosmological implications of spectator and dynamical fields during inflation

Some possible cosmological implications of the inclusion of spectator gauge elds in the inationary action are considered. In this context, a spec-tator eld is a eld that is not directly responsible for ination but can aect cosmological observables. Spectator gauge elds can lead to novel and distinguishable features in inationary models (as compared to single-eld ination) that may be detectable. A model of anisotropic ination is considered where universal anisotropy is maintained through a vector eld that is coupled to both the inaton and its derivative. The derivative cou-pling reduces the anisotropy induced when compared to the non-derivative case, reducing tension with observations. SU(N) gauge elds appear natu-rally in the actions of string ination models. The inclusion of an SU(N) gauge eld coupled both to scalars and pseudo-scalars (axions) is considered in two models of string ination whose inatons are K¨ahler moduli: K¨ahler moduli ination and bre ination. It is shown that the coupling between the axion and the gauge eld can lead to a large (chiral) enhancement of the tensor spectrum of these two models. In the case of K¨ahler moduli ination, a model that generically predicts an unobservable value for the tensor-to-scalar ratio (r 10−3), this enhancement is capable of boost-ing the tensor-to-scalar ratio to values that will be potentially observable at next generation detectors. However, the parameters required to achieve this goal may present a challenge for its successful realisation in string theory. In the case of bre ination, a model that generically predicts an observable value for the tensor-to-scalar ratio, it is shown that this enhancement can render the tensor spectrum of bre ination almost entirely chiral, giving it a distinguishable feature that may be detectable.