Systematics of aligned axions

Abstract

We describe a novel technique that renders theories of N axions tractable, and more generally can be used to efficiently analyze a large class of periodic potentials of arbitrary dimension. Such potentials are complex energy landscapes with a number of local minima that scales as sqrt{N!} , and so for large N appear to be analytically and numerically intractable. Our method is based on uncovering a set of approximate symmetries that exist in addition to the N periods. These approximate symmetries, which are exponentially close to exact, allow us to locate the minima very efficiently and accurately and to analyze other characteristics of the potential. We apply our framework to evaluate the diameters of flat regions suitable for slow-roll inflation, which unifies, corrects and extends several forms of “axion alignment” previously observed in the literature. We find that in a broad class of random theories, the potential is smooth over diameters enhanced by N3/2 compared to the typical scale of the potential. A Mathematica implementation of our framework is available online.