Speaker: Sreemanti Chakraborti (Durham Univ.)

In this talk, I will discuss axion-like particles (ALP) as dark matter candidates in the “ultralight mass regime”. On the theory side, I will elaborate on the consistent treatment of QFT of an ALP interacting with Standard Model fields accounting for the renormalisation group running and matching to the low-energy theory. A plethora of quantum sensor experiments has been designed to search for very light ALPs that are particularly sensitive to these effects because they probe large values of the decay constant for which running effects become important. In addition, while linear axion interactions are set by its pseudoscalar nature, quadratic interactions are indistinguishable from scalar interactions. This makes the two types of interactions sensitive to different categories of experiments. I will discuss the reach of various experiments exploiting quantum technology via quantum sensors, haloscopes, helioscopes, and fifth force searches. Lastly, I will discuss the nonlinear behaviour of the ALP field close to the surface of the earth and identify the experiments impacted by this effect.