HET Seminar: "Friendship in the Axiverse" Jed Thompson (Stanford)

"Friendship in the Axiverse"

A generic low-energy prediction of string theory is the existence of a large collection of axions commonly known as a string axiverse.  In a realistic axiverse, string axions can be distributed densely over many orders of magnitude of mass, and are expected to interact with one another through a joint potential.  I will show that non-linearities in this potential lead to a new type of resonant energy transfer between axions with nearby masses.  This resonance is not captured by linearized treatments previously discussed in the literature, and generically results in a transfer of energy density from axions with larger decay constants to those with smaller decay constants, leading to a multitude of late-time signatures.  These include enhanced direct detection prospects for a resonant pair comprising even a small subcomponent of dark matter (DM), and boosted small-scale structure if the pair is the majority of DM.  Near-future iterations of experiments such as ADMX and DM Radio will be sensitive to this scenario, as will astrophysical probes of DM substructure.