Primordial black holes and magnetic fields in conformal neutrino mass models

TL;DR

This paper explores how phase transitions in conformal U(1)′ models can generate primordial black holes, magnetic fields, and gravitational waves, linking these phenomena to neutrino physics and future observational signals.

Contribution

It demonstrates the connection between phase transition scales, PBH production, magnetic field generation, and gravitational wave signals in a unified conformal neutrino mass model.

Findings

Phase transitions at seesaw scales produce detectable gravitational waves.

PBHs can account for dark matter within certain mass ranges.

Magnetic fields generated are above current observational bounds.

Abstract

Sufficiently strong and long-lasting first-order phase transitions can produce primordial black holes (PBHs) that contribute substantially to the dark matter abundance of the Universe, and can produce large-scale primordial magnetic fields. We study these mechanisms in a generic class of conformal $\mathrm{U(1)}^\prime$ models that also explain active neutrino oscillation data via the type-I seesaw mechanism. We find that phase transitions that occur at seesaw scales between $10^4$ GeV and $10^{11}$ GeV produce gravitational wave signals (from the dynamics of the phase transition and from the decay of cosmic string loops) at LISA/ET that can be correlated with microlensing signals of PBHs at the Roman Space Telescope, while scales near $10^{11}$ GeV can be correlated with Hawking evaporation signals at future gamma-ray telescopes. LISA can probe the entire range of PBH masses between $1\times 10^{-16}M_\odot$ and $8\times 10^{-11}M_\odot$ if PBHs fully account for the dark matter abundance. For Z' masses between 5 TeV and 100 TeV, and $\sim 3$ TeV right-handed neutrinos, helical magnetic fields can be produced with magnitudes $\sim 10^{-16}$-$10^{-13}$ G and coherence lengths $\sim 10^{-4}$-$10^{-2}$ Mpc, above current blazar lower bounds.