Tilt and Tensor-to-Scalar Ratio in Multifield Monodromy Inflation

Abstract

We study the possible range of the tilt $n_s$ and the tensor-to-scalar ratio $r$ in multifield versions of a class of inflationary models from string theory. We show that $r$ is the same between the single field models and multifield models while $n_s$ is bounded above by the results of single field models. Below its maximum value, $n_s$ depends on the specific distributions of parameters in the model. The general trend is that the wider the distributions are, the smaller $n_s$ is. We show that $n_s$ does not have a rigorous lower bound. It is argued, however, that models predicting arbitrarily small $n_s$ only constitute a small portion of the possible ones and for the vast majority of models, $n_s$ is bounded below by predictions given by models with uniformly distributed parameters.