Natural inflation with multiple sub-Planckian axions

Abstract

We extend the Kim-Nilles-Peloso (KNP) alignment mechanism for natural inflation to models with N > 2 axions, which obtains super-Planckian effective axion decay constant f(eff) >> M-P1 through an alignment of the anomaly coefficients of multiple axions having sub-Planckian fundamental decay constants f(0) << M-P1. The original version of the KNP mechanism realized with two axions requires that some of the anomaly coefficients should be of the order of feft/fo, which would be uncomfortably large if f(eff)/f(0) greater than or similar to O(100) as suggested by the recent B10EP2 results. We note that the KNP mechanism can be realized with the anomaly coefficients of C)(I) if the number of axions N is large as N1nN greater than or similar to 2 In(f(eff)/f(0)), in which case the effective decay constant can be enhanced as f(eff)/f(0) similar to root N!n (N-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 similar to f(eff)(2)/f(0)(2), 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 O(f(0)/f(eff)) under a random choice of the anomaly coefficients. We also present a simple model realizing a multiple axion monodromy along the inflaton direction.