Running of the Spectrum of Cosmological Perturbations in String Gas Cosmology

Understand

We compute the running of the spectrum of cosmological perturbations in String Gas Cosmology, making use of a smooth parametrization of the transition between the early Hagedorn phase and the later radiation phase.

• We find that the running has the same sign as in simple models of single scalar field inflation.
• Its magnitude is proportional to $(1 - n_s)$ ($n_s$ being the slope index of the spectrum), and it is thus parametrically larger than for inflationary cosmology, where it is proportional to $(1 - n_s)^2$.