Preheating in bubble collisions

In a landscape with metastable minima, the bubbles will inevitably nucleate. We show that when the bubbles collide, due to the dramatic oscillation of the field at the collision region, the energy deposited in the bubble walls can be efficiently released by the explosive production of the particles. In this sense, the collision of bubbles is actually highly inelastic. The cosmological implications of this result are discussed.

Figure 1

The potential with two minima, which will be used in the numerical simulations of the bubble collision in Figs. 2, 4, and the production of $\chi$-particle in collision region in Fig. 3. $\eta \equiv |{\varphi }_T-{\varphi }_F|$ is a normalized parameter with mass dimension. The parameter we used is $\eta =0.01$ for the whole paper.

Figure 2

The numerical simulation of bubble collision. The color panel describes the evolution and collision of bubbles after their nucleations, where the light gray region denotes the region in ${\varphi }_T$ while the black region denotes that in ${\varphi }_F$, and the dark gray region between them denotes the bubble wall. We can see that during the bubbles collision, the bubble walls will be oscillating around the center of the bubbles collision, which induces that at the collision region the field $\varphi$ initially in ${\varphi }_F$ overshoots to ${\varphi }_T$ and then backs to ${\varphi }_F$, and oscillates around ${\varphi }_F$. The lower panel is that of ${\varphi }_C$ in the color panel. Here $M_F\sim 0.04\eta$.

Figure 3

The numerical simulation of the evolution of $X_k$ at the collision region for the coupling (2). $\eta =0.01$, $g^2=0.5$, and the modes shown are $k=0$ and $k=0.1\eta$, respectively. We also show the evolution of ${\varphi }_C$ in dark gray lines.

Figure 4

The numerical simulation of bubble collisions, in which the release of walls energy induced by the production of particles at the time of each collision of bubble walls is included, ${\varphi }_{*}=0.4$. The color panel describes the oscillation of bubble walls during the bubble collision. What the light gray region, the black region, and the dark gray region denote are the same as that in Fig. 2. The lower panel is that of ${\varphi }_C$ in the color panel.