Abstract

String axions have been proposed as candidates for solving several puzzles in cosmology. In this talk, I will focus on axions as dark matter. After reviewing how string axions can occur in our universe, I will provide a string theoretical explanation of dark matter as composed of axions coming from type IIB string theory. Based on the latest bounds, I will show how likely it is for dark matter to be composed of such particles and in which abundance, and I will provide predictions on the preferred ranges of masses and decay constants. On the contrary, requiring the axions to lie in a particular range of the parameter space imposes constraints on the UV theory. I will focus both on the role of moduli stabilization and the landscape of string vacua. Finally, I will discuss axion production at the end of inflation and the implications for the proposed cosmic axion background.