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...
In this talk I discuss the gravitational wave signals of dynamical axion models. In particular, I focus on models which solve the strong CP problem and include the confinement of a QCD-like gauge group at the TeV scale. Interestingly, the amplitude of the gravitational wave spectrum depends on the mass of the dynamical axion. The resulting spectra may be observed at future mid-range...
