Cosmic birefringence is predicted if an axion-like particle (ALP) moves after the recombination epoch. We show that this naturally happens if the ALP is coupled to the dark matter density because it then acquires a large effective mass after the matter-radiation equality. We give a simple model to realize this scenario, where dark matter is made of hidden monopoles, which give the ALP such a...
We study new signatures associated with electromagnetic properties of axion strings. We focus
on charge deposition onto axion strings from electromagnetic fields and
the subsequent novel neutralizing
mechanisms due to bound state formation. While early universe
signatures appear unlikely, there are a plethora of late time
signatures. Axion strings passing through galaxies obtain an...
Black hole superradiance is a powerful probe of light, weakly-coupled hidden sector particles. Particles with a Compton wavelength comparable to the black hole’s radius lead to an instability, extracting mass and angular momentum from the black hole. Many ultralight candidates, such as axions, generically have self-interactions that can influence the evolution of the superradiant instability. ...
