We confront the warm inflation observational predictions directly with the latest CMB data. We focus on a linear temperature (T ) dissipative coefficient combined with the simplest model of inflation, a quartic chaotic potential. Although excluded in its standard cold inflation version, dissipation reduces the tensor-to-scalar ratio and brings the quartic chaotic model within the observable allowed range. We will use the CosmoMC package to derive constraints on the model parameters: the combination of coupling constants giving rise to dissipation, the effective number of relativistic degrees of freedom contributing to the thermal bath, and the quartic coupling in the inflaton potential. We do not assume a priori a power-law primordial spectrum, neither we fix the no. of e-folds at the horizon exit. The relation between the no. of e-folds and the comoving scale at horizon crossing is derived from the dynamics, depending on the parameters of the model, which allows us to obtain the k-dependent primordial power spectrum. We study the two possibilities considered in the literature for the spectrum, with the inflaton fluctuations having a thermal or a non-thermal origin, and discuss the ability of the data to constraint the model parameters.

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A dark radiation term arises as a correction to the energy momentum tensor in the simplest five-dimensional RS-II brane-world cosmology. In this paper we revisit the constraints on dark radiation based upon the newest results for light-element nuclear reaction rates, observed lightelement abundances and the power spectrum of the Cosmic Microwave Background (CMB). Adding dark radiation during big bang nucleosynthesis alters the Friedmann expansion rate causing the nuclear reactions to freeze out at a different temperature. This changes the final light element abundances at the end of BBN. Its influence on the CMB is to change the effective expansion rate at the surface of last scattering. We find that our adopted BBN constraints reduce the allowed range for dark radiation to between −12.1% and +6.2% of the ambient background energy density. Combining this result with fits to the CMB power spectrum, the range decreases to −6.0% to +6.2%. Thus, we find, that the ratio of dark radiation to the background total relativistic mass energy density ρDR/ρ (fixed at 10 MeV) is consistent with zero although in the BBN analysis there could be a slight preference for a negative contribution. However, the BBN constraint depends strongly upon the adopted primordial helium abundance.

We summarize some applications of big bang nucleosythesis (BBN) and the cosmic microwave background (CMB) to constrain the first moments of the creation of matter in the universe. We review the basic elements of BBN and how it constraints physics of the radiation-dominated epoch. In particular, how the existence of higher dimensions impacts the cosmic expansion through the projection of curvature from the higher dimension in the "dark radiation" term. We summarize current constraints from BBN and the CMB on this brane-world dark radiation term. At the same time, the existence of extra dimensions during the earlier inflation impacts the tensor to scalar ratio and the running spectral index as measured in the CMB. We summarize how the constraints on inflation shift when embedded in higher dimensions. Finally, one expects that the universe was born out of a complicated multiverse landscape near the Planck time. In these moments the energy scale of superstrings was obtainable during the early moments of chaotic inflation. We summarize the quest for cosmological evidence of the birth of space-time out of the string theory landscape. We will explore the possibility that a superstring excitations may have made itself known via a coupling to the field of inflation. This may have left an imprint of "dips" in the power spectrum of temperature fluctuations in the cosmic microwave background. The identification of this particle as a superstring is possible because there may be evidence for different oscillator states of the same superstring that appear on different scales on the sky. It will be shown that from this imprint one can deduce the mass, number of oscillations, and coupling constant for the superstring. Although the evidence is marginal, this may constitute the first observation of a superstring in Nature.