Dr. Pranjal Trivedi

Axions and axion-like particles are leading cold dark matter candidates motivated by the Peccei-Quinn solution to the strong CP-problem. They also arise generically in many extensions of the Standard Model (eg. 'axiverse'). I will review some ideas at the forefront of the hunt for axion dark matter and compare laboratory searches to astrophysical and cosmological probes of axions. I will then focus on how cosmological birefringence can be a unique signal of the parity-violating axion constituting dark matter. Axion dark matter produces a rotation of the linear polarization of the cosmic microwave background (CMB). Considering the oscillating axion field at both recombination and at the observer, we can improve constraints on the axion-photon coupling by several orders, over a wide range of axion mass, up to the fuzzy dark matter scale. Recent evidence of birefringence in the Planck CMB data could be an axion signal and future CMB observations have the potential to precisely probe the properties of axion dark matter.