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arXiv · 0904.0647

Isocurvature forecast in the anthropic axion window

J. Hamann·S. Hannestad·G. G. Raffelt·Y. Y. Y. Wong
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Abstract

We explore the cosmological sensitivity to the amplitude of isocurvature fluctuations that would be caused by axions in the "anthropic window" where the axion decay constant f_a >> 10^12 GeV and the initial misalignment angle Theta_i << 1. In a minimal Lambda-CDM cosmology extended with subdominant scale-invariant isocurvature fluctuations, existing data constrain the isocurvature fraction to alpha < 0.09 at 95% C.L. If no signal shows up, Planck can improve this constraint to 0.042 while an ultimate CMB probe limited only by cosmic variance in both temperature and E-polarisation can reach 0.017, about a factor of five better than the current limit. In the parameter space of f_a and H_I (Hubble parameter during inflation) we identify a small region where axion detection remains within the reach of realistic cosmological probes.

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J. Hamann, S. Hannestad, G. G. Raffelt, Y. Y. Y. Wong. 2009-04-03. Isocurvature forecast in the anthropic axion window. https://doi.org/10.1088/1475-7516/2009/06/022

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