Isocurvature forecast in the anthropic axion window

2009/04/30 by J. Hamann, S. Hannestad, G. G. Raffelt +1 · 2 citations
Physics and Astronomy · #hep-ph #astro-ph.CO

paper · pdf · doi:10.1088/1475-7516/2009/06/022

published as JCAP 0906:022,2009 · 14 pages, 4 figures; v2: matches published version

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 >> 10¹2 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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