Speaker
Description
Classically scale-invariant (conformal) extensions of the Standard Model with a broken $U(1)^\prime$ can provide a mechanism for neutrino mass generation and feature potentially measurable signatures in cosmology. I summarize our results for supercooled first-order phase transitions in conformal neutrino-mass models and their multi-messenger implications. The transition can produce a stochastic gravitational-wave background detectable across nHz-kHz bands, enabling interferometers and pulsar-timing arrays to constrain (or measure) the $U(1)^\prime$ breaking scale and the associated seesaw scale. We identify parameter regions where the nHz signal is naturally enhanced and can match current PTA hints while remaining consistent with cosmological bounds. I then discuss correlated outcomes of prolonged supercooling: sizeable primordial black-hole production that can constitute a substantial fraction of dark matter, and the generation of helical primordial magnetic fields with potentially observable strengths and coherence lengths. Overall, these models provide a concrete, testable link between the origin of neutrino mass and potential observations of gravitational waves, PBHs, and cosmic magnetism.
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