Speaker
Description
Conventional approaches to probing axions and axion-like particles (ALPs)typically rely on a coupling to photons. However, if this coupling is extremely weak, ALPs become invisible and are effectively decoupled from the Standard Model. We show that such invisible axions, which are viable candidates for dark matter, can produce a stochastic gravitational wave background in the early universe and are therefore audible. This signal is generated in models where the invisible axion couples to a dark gauge boson that experiences a tachyonic instability when the axion begins to oscillate. Quantum fluctuations in the gauge boson get exponentially amplified and source chiral gravitational waves. We present lattice calculations of the resulting GW signal and highlight its detectability. Furthermore we give an outlook on possible model implementations.
