Supersonic Electroweak Baryogenesis: Achieving Baryogenesis for Fast Bubble Walls

TL;DR

The paper tackles baryogenesis during a strongly first-order electroweak transition with supersonic bubble walls by exploiting heating behind detonations to nucleate symmetric-phase bubbles inside broken-bubble volumes. These symmetric bubbles, which nucleate near the detonation wall, slowly expand and then contract as the detonation progresses, allowing diffusion-driven baryogenesis to occur in their contracting phase and transfer to the broken phase. The authors develop a hydrodynamic framework, analyze symmetric-bubble nucleation and growth, and quantify the required volume filling factor for viable baryogenesis. They demonstrate viability in a Higgs portal model with multiple singlets, identifying regions in parameter space where T− > Tc and Υ is sizable, suggesting a potential link between baryogenesis and gravitational waves in such scenarios.

Abstract

Standard electroweak baryogenesis in the context of a first order phase transition is effective in generating the baryon asymmetry of the universe if the broken phase bubbles expand at subsonic speed, so that CP asymmetric currents can diffuse in front of the wall. Here we present a new mechanism for electroweak baryogenesis which operates for supersonic bubble walls. It relies on the formation of small bubbles of the symmetric phase behind the bubble wall, in the broken phase, due to the heating of the plasma as the wall passes by. We apply the mechanism to a model in which the Higgs field is coupled to several singlets, and find that enough baryon asymmetry is generated for reasonable values of the parameter space.

Figures (14)

• Figure 1: The solutions for the plasma velocity $v(\xi)$ (LEFT) and temperature $T(\xi)/T_N$ (RIGHT) in the case of a detonation (for $v_w = 0.76$ and $\alpha_N = 0.078$). The dashed-red horizontal line corresponds to $T_N$ and the solid-blue horizontal line corresponds to $T_c$.
• Figure 2: Motion of plasma volume elements (black lines) as the detonation wave (in grey) sweeps through them, for different values of the initial distance $r_0$ to the center of the bubble.
• Figure 3: Region in the ($\alpha_N, v_w$)-plane for which $T_- > T_c$ (\ref{['eq:Heating']}), for $a_-/a_+ = 0.85$. The dashed-red line corresponds to $v_w = \tilde{v}_w$ (lower bound on $v_w$), and the lower bound on $\alpha_N$ (dashed-black line) corresponds to the occurence of the hydrodynamic obstruction in the deflagration caseKN. The different values of $f_b$ (RIGHT) correspond to different sizes of the region where $T > T_c$ with respect to the size of the bubble (\ref{['cb']}).
• Figure 4: Region in the ($a_-/a_+, v_w$)-plane for which $T_- > T_c$ (\ref{['eq:Heating']}), for $\alpha_N = 0.1$. As in Figure \ref{['fig:3']}, the dashed-red line corresponds to $v_w = \tilde{v}_w$ (lower bound on $v_w$).
• Figure 5: LEFT: Evolution of the potential $V(\phi,T)$ with temperature in the case of a first order phase transition in the early universe (see section \ref{['symmetric_nucleation1']}). RIGHT: Local change in the potential for the case $T_{-} > T_c$ (see section \ref{['symmetric_nucleation2']}).