Looking for New Physics with Primordial Gravitational Waves

Our current theory of fundamental physics, the Standard Model of elementary particles, describes remarkably well the physics at the smallest scales, and the state of the Universe one trillionth of a second after the Big Bang onward. Nevertheless, it is not a complete description of Nature since many questions remain unanswered, including: What is dark matter? What is the origin of the matter-antimatter asymmetry? How do neutrinos get their masses? In this talk, I will demonstrate how measuring the primordial stochastic gravitational wave background can help us shed light on those puzzles. In particular, I will show the expected gravitational wave signatures of models with extended gauge groups addressing the most pressing issues in modern particle physics. Those signals are generated by various phenomena in the early Universe such as: first order phase transitions, dynamics of cosmic strings, and domain wall annihilation. The expected gravitational wave spectrum lies within the reach of current and upcoming experiments: gravitational wave interferometers, pulsar timing arrays, and astrometric observations.