Bayesian reconstruction of the inflaton’s speed of sound using CMB data

We update the search for features, due to transient reductions in inflaton's speed of sound, Cosmic Microwave Background (CMB) angular power spectrum using Planck 2018 temperature, polarization and lensing data. develop a new methodology test more flexible templates reconstruct reduction sound based on Gaussian Processes. formally derive dynamical prior shape \textit{maximum-entropy} approach ensure physical conditions model are satisfied. The posterior allows one or consecutive reductions, fitting apparent features CMB spectra multipoles from few tens $\ell\simeq 2000$. As expected, these fits not statistically favored with respect $\Lambda$CDM model. derived here inclusion additional data sets (in particular, Large Scale Structure data), which principle will increase statistical significance reconstruction sound.