Cosmological window onto the string axiverse and the supersymmetry breaking scale


The low-energy limit of several string theories feature the axiverse, a plethora of light axions with masses spanning various orders of magnitude. Within the simplest picture, the masses of the resulting axions depend on a hard non-perturbative scale related to the supersymmetry breaking scale $M_{\rm susy}$, and the dimensionless instanton action $S$ responsible for breaking the axion shift symmetry. We explore whether these two parameters can be probed using cosmology, taking into account current limits on the tensor-to-scalar ratio and the primordial isocurvature fraction, and measurements of the dark matter energy density today. Adopting string-inspired flat priors on $\log_{10}M_{\rm susy}$ and $S$, and imposing that $M_{\rm susy}$ be sub-Planckian, we find $S=198\pm28$ at 68%~C.L., in striking agreement with the theoretical expectation that $S \approx 200$, whereas $M_{\rm susy}$ remains unconstrained.

Physical Review D 99, 063517 (2019)
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Luca Visinelli
Luca Visinelli
Fellini - Marie Skłodowska-Curie Fellow

PhD in Physics, working on Particle Astrophysics and Dark Matter modeling.