Constraints on superstrings, inflation, and extra dimensions from the CMB and big bang nucleosynthesis

Abstract

The energy scale of superstrings was obtainable iduring the early moments of chaotic inflation out of the string theory landscape. This talk explores the possibility that a specific superstring excitation may have made itself known via its 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. At the same time, the existence of extra dimensions during inflation impacts the tensor to scalar ratio and the running spectral index. We summarize how the constraints on inflation shift when embedded in higher dimensions. Finally, higher dimensions also impact 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.