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Register a new userMagnetic field generation from bubble collisions during first-order phase transition
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We study the magnetic fields generation from the cosmological first-order electroweak phase transition. We calculate the magnetic field induced by the variation of the Higgs phase for two bubbles and three bubbles collisions. Our study shows that electromagnetic currents in the collision direction produce the ring-like magnetic field in the intersect regions of colliding bubbles, which may seed the primordial magnetic field that are constrained by intergalatic field observations.
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We perform the three dimensional lattice simulation of the magnetic field and gravitational wave productions from bubble collisions during the first-order electroweak phase transition. Except that of the gravitational wave, the power-law spectrum of the magnetic field strength is numerically calculated for the first time, which is of a broken power-law spectrum: $B_{xi}propto f^{0.91}$ for low frequency region of $f<f_star$ and $B_{xi}propto f^{-1.65}$ for high frequency region of $f>f_star$ in the thin-wall limit, with the peak frequency being $f_starsim 5$ Hz at the phase transition temperature 100 GeV. When the hydrodynamics is taken into account, the generated magnetic field strength can reach $B_xisim 10^{-7}$G at a correlation length $xisim 10^{-7}$pc, which may seed the large scale magnetic fields. Our study shows that the measurements of cosmic magnetic field strength and gravitational waves are complementary to probe new physics admitting electroweak phase transition.
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.
We study strongly supercooled cosmological phase transitions. We perform numerical lattice simulations of two-bubble collisions and demonstrate that, depending on the scalar potential, in the collision the field can either bounce to a false vacuum or remain oscillating around the true vacuum. We study if these cases can be distinguished from their gravitational wave signals and discuss the possibility of black hole formation in the bubble collisions.
Primordial black holes (PBHs) produced in the early Universe have attracted wide interest for their ability to constitute dark matter and explain the compact binary coalescence. We propose a new mechanism of PBH production during first-order phase transitions (PTs) and find that PBHs are naturally produced during PTs model-independently. Because of the randomness of the quantum tunneling, there always exists some probability that the vacuum decay is postponed in a whole Hubble volume. Since the vacuum energy density remains constant while radiation is quickly redshifted in the expanding Universe, the postponed vacuum decay then results in overdense regions, which finally collapse into PBHs as indicated by numerical simulations. Utilizing this result one can obtain mutual predictions and constraints between PBHs and GWs from PTs. The predicted mass function of PBHs is nearly monochromatic. We investigate two typical cases and find that 1) PBHs from a PT constitute all dark matter and GWs peak at $1$Hz, 2) PBHs from a PT can explain the coalescence events observed by LIGO-Virgo collaboration, and meanwhile GWs can explain the common-spectrum process detected by NANOGrav collaboration.
We discuss the possibility of forming primordial black holes during a first-order phase transition in the early Universe. As is well known, such a phase transition proceeds through the formation of true-vacuum bubbles in a Universe that is still in a false vacuum. When there is a particle species whose mass increases significantly during the phase transition, transmission of the corresponding particles through the advancing bubble walls is suppressed. Consequently, an overdensity can build up in front of the walls and become sufficiently large to trigger primordial black hole formation. We track this process quantitatively by solving a Boltzmann equation, and we determine the resulting black hole density and mass distribution as a function of model parameters.
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