Abstract
We discuss gravitational wave (GW) signals of cosmological origin, generated in the early universe. We argue that early universe GW backgrounds are always of stochastic nature and describe their general properties and their evolution during cosmological expansion. We present examples of relevant early universe GW generation mechanisms, as well as the properties of the GW backgrounds they produce. In particular, we discuss (1) GWs from first-order phase transitions and (2) GWs from topological defects, with a particular emphasis on cosmic strings. The phenomenology of early universe GW sources is extremely rich, possibly leading to GW backgrounds within the reach of near-future detectors. The detection of any of these stochastic signals would be a milestone in physics, providing crucial information on the high-energy physics characterizing the early universe, probing energy scales well beyond the reach of present and planned particle accelerators.
Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
