Astrophysical Observables of Cosmic First Order Phase Transitions
Cosmic first order phase transitions in the early Universe can lead to several observable consequences like the production of magnetic fields and gravitational waves. Several well-motivated extensions of the Standard Model predict a first order electroweak phase transition. In the first part of this presentation, we use numerical simulations to study the production of magnetic fields in the first order electroweak phase transition, with the help of a scheme for random bubble nucleation. We find that about 10% of the latent heat is converted into magnetic energy, with most of the magnetic fields being generated after the phase transition when the Higgs oscillates around the true vacuum. The energy spectrum of the magnetic field has a peak that shifts towards larger length scales as the phase transition unfolds. By the end of our runs the peak wavelength is of the order of the bubble percolation scale, or about a third of our lattice size. In the second part of the presentation, we study the generation of gravitational waves from a first order phase transition induced by an axion-like particle (ALP) at some high energy scale fa. We show that if the ALP has a nonzero coupling to the Standard Model Higgs boson, the phase transition could be first order, thereby producing stochastic gravitational waves that are potentially observable in current and future gravitational-wave detectors such as TianQin, Big Bang Observer (BBO) and Cosmic Explorer (CE). The gravitational wave detection prospects are independent of the ALP mass and largely complementary to current laboratory, astrophysical and cosmological probes of these scenarios.