Gravitational Waves from the Early Universe

Gravitational waves promise a new window into the highest-energy events in the evolution of the universe. The recent LIGO/Virgo detections of gravitational waves from the mergers of binary black holes and binary neutron stars and have ignited interest in the future direction of gravitational wave astronomy. A space-based laser interferometer, pioneered by NASA's LISA concept and the European Space Agency's eLISA program and ESA's recent spectacularly successful LISA Pathfinder mission, would enable direct detection of gravitational waves in the milliHertz range. A lower frequency range would allow detection of supermassive black hole mergers, tracing the galaxy merger history and serving as cosmic sirens to probe the universe's expansion history, as well as precursors for the LIGO sources. A space-based detector would also be sensitive to stochastic gravitational wave backgrounds produced by unknown physics operating in the very early universe, including an electroweak phase transition. This Nordita program will bring scientists together to engage in an effort to characterize and detect sources contributing to the gravitational wave background from the early universe, and the implications for new physics at the TeV scale and beyond.