# Intergalactic Magnetic Fields from First-Order Phase Transitions

## TL;DR

This paper investigates the generation of intergalactic magnetic fields during early Universe first-order phase transitions, analyzing models that could produce observable magnetic fields, gravitational waves, and collider signatures.

## Contribution

It compares two models for early Universe phase transitions, assessing their potential to generate detectable magnetic fields, gravitational waves, and collider signals.

## Key findings

- Bubble collisions alone are insufficient for large magnetic fields in SM+$H^6$
- Turbulence can generate magnetic fields above observational bounds in SM+$H^6$
- Both models can produce observable gravitational waves and collider signatures if magnetic fields are strong enough

## Abstract

We study the generation of intergalactic magnetic fields in two models for first-order phase transitions in the early Universe that have been studied previously in connection with the generation of gravitational waves (GWs): the Standard Model supplemented by an $|H|^6$ operator (SM+$H^6$) and a classically scale-invariant model with an extra gauged U(1) $B - L$ symmetry (SM$_{B-L}$). We consider contributions to magnetic fields generated by bubble collisions and by turbulence in the primordial plasma, and we consider the hypotheses that helicity is seeded in the gauge field or kinetically. We study the conditions under which the intergalactic magnetic fields generated may be larger than the lower bounds from blazar observations, and correlate them with the observability of GWs and possible collider signatures. In the SM+$H^6$ model bubble collisions alone cannot yield large enough magnetic fields, whereas turbulence may do so. In the SM$_{B-L}$ model bubble collisions and turbulence may both yield magnetic fields above the blazar bound unless the B$-$L gauge boson is very heavy. In both models there may be observable GW and collider signatures if sufficiently large magnetic fields are generated.