Gravitational Wave Signatures of Unification and Dark Matter

I will demonstrate that a new and unique gravitational wave signal is expected in particle physics models with gauge symmetries broken at vastly different energy scales. The spectrum consists of a double-peak structure consisting of a sharp peak from domain walls and a smooth bump from a first order phase transition in the early Universe. As an example, I will consider a model with baryon number and color unified into an SU(4) gauge group and lepton number generalized to an SU(2) gauge symmetry. The model contains two types of dark matter particles, explains the matter-antimatter asymmetry of the Universe, and accommodates nonzero neutrino masses. I will discuss how future gravitational wave experiments, such as LISA, Big Bang Observer, DECIGO, Einstein Telescope, and Cosmic Explorer, can search for this novel signature.