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Description
In 2023, pulsar timing array (PTA) collaborations around the globe announced evidence for a nanohertz gravitational-wave background (GWB) — a breakthrough achievement with important implications for astrophysics and particle physics. The most common interpretation of the new signal is that it originates from a cosmic population of supermassive black-hole binaries. At present, it is, however, also conceivable that it represents a gravitational-wave echo of the Big Bang. In my talk, I will focus on the latter possibility and illustrate how PTA data can be used to probe particle physics beyond the Standard Model (BSM) in the early Universe. Along the way, I will highlight certain exotic interpretations of the PTA signal, for instance, axion spectator dynamics during cosmic inflation, and comment on the gravitational-wave phenomenology of axion inflation in more general terms. Finally, I will conclude with a brief outlook and explain how future PTA data will help in discriminating between a GWB signal of astrophysical origin and a GWB signal from the Big Bang.
Organised by
Diptaparna Biswas
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