Axions from Strings: the Attractive Solution

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We study the system of axion strings that forms in the early Universe if the Peccei-Quinn symmetry is restored after inflation.

• Using numerical simulations, we establish the existence of an asymptotic solution to which the system is attracted independently of the initial conditions.
• We study in detail the properties of this solution, including the average number of strings per Hubble patch, the distribution of loops and long strings, the way that different types of radiation are emitted, and the shape of the spectrum of axions produced.
• We find clear evidence of logarithmic violations of the scaling properties of the attractor solution.