Ultralight dark matter (ULDM) is an alternative to particle-like cold dark matter (CDM) that has attracted much recent attention. While ULDM's large scale structure is similar to that of conventional CDM, its small particle mass means that it differs on small scales. In this talk, I will introduce and motivate ultralight dark matter and its unique signatures. I will then present simulations of ULDM in three domains:
1. Self-interactions in ULDM affect the efficiency with which small dark matter halos are tidally stripped.
2. Rotation in ULDM can manifest as vortices. These vortices are generically unstable, but gravitational effects from supermassive black holes may cause them to persist indefinitely.
3. ULDM as motivated by string theory may consist of a spectrum of particles with different properties. The existence of multiple ultralight species would change the predicted small-scale structure.
If time permits, I will discuss how similar simulations can describe reheating in the epoch between inflation and big bang nucleosynthesis.