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Inflation from a chaotic potential with a step

Abstract:

In this work, we study the effects on the relevant observational parameters of an inflationary universe from a chaotic potential with a step. We numerically evolve the perturbation equations within both cold inflation and warm inflation. On the one hand, in a cold inflation scenario we analyse the scalar power spectrum PR in terms of the number of e-folds Ne, and in terms of the ratio k/k0, where k0 is our pivot scale. We show how PR oscillates around 0.2<k/k0<20. Additionally, we present the evolution of two relevant parameters: the scalar spectral index ns and the tensor-to-scalar ratio r. In fact, more than one region of (ns,r) lies within the observable window (Planck 2018). On the other hand, in the warm inflationary case, we also examine the evolution of PR in terms of Ne and k/k0. Perturbations are amplified in WI; in fact, PR can be much larger than the CMB value PR>2.22×10−9. This time, the spectral index ns is clearly blue-tilted, at smaller scales, and the tensor-to-scalar ratio r becomes too low. However, ns can change from blue-tilted towards red-tilted, since PR starts oscillating around k/k0∼40. Indeed, the result from the step potential skims the Planck contours. Finally, one key aspect of this research was to contrast the features of an inflationary potential between both paradigms, and, in fact, they show similarities and differences. Due to a featured background and a combined effect of entropy fluctuations (only in warm inflation), in both scenarios certain fluctuation scales are not longer “freeze in” on super-horizon scales. In contrast, warm inflation boosts the growth of the amplitude of the primordial spectrum, whilst moving the oscillatory behaviour from the feature scale k/k0∼1 (manifested in cold inflation) to k/k0∼40; although not only the step potential wiggles, but also the chaotic. This might indicate that warm inflation could function as a screening mechanism capable of smoothing the feature of the inflationary potential; however, further investigation is required to corroborate this.