2014/04/30 by Kiwoon Choi, Hyungjin Kim, Seokhoon Yun · 1 citation
Physics and Astronomy · #hep-th #astro-ph.CO #hep-ph
paper · pdf · doi:10.1103/physrevd.90.023545
published as Phys. Rev. D 90, 023545 (2014) · 19 pages, 2 figures. v2: typos corrected, references added, some arguments improved. v3: references added, examples added. v4: references added, matches published version
arxiv created 2014/09/08 · arxiv updated 2014/09/09
We extend the Kim-Nilles-Peloso (KNP) alignment mechanism for natural inflation to models with N>2 axions, which obtains a super-Planckian effective axion decay constant f_\textrmeff≫ MPl through an alignment of the anomaly coefficients of multiple axions having sub-Planckian fundamental decay constants f0≪ MPl. The original version of the KNP mechanism realized with two axions requires that some of the anomaly coefficients should be of the order of f_\textrmeff/f0, which would be uncomfortably large if f\rm eff/f0 \gtrsim \cal O(100) as suggested by the recent BICEP2 results. We note that the KNP mechanism can be realized with the anomaly coefficients of O(1) if the number of axions N is large as Nln N\gtrsim 2ln (f_\textrmeff/f0), in which case the effective decay constant can be enhanced as f\rm eff/f0 ∼ √(N !) nN-1 for n denoting the typical size of the integer-valued anomaly coefficients. Comparing to the other multiple axion scenario, the N-flation scenario which requires N ∼ f_\textrmeff2/f02, the KNP mechanism has a virtue of not invoking to a too large number of axions, although it requires a specific alignment of the anomaly coefficients, which can be achieved with a probability of \cal O(f0/f\rm eff) under a random choice of the anomaly coefficients. We also present a simple model realizing a multiple axion monodromy along the inflaton direction.