Cosmic strings from preheating

Abstract

We investigate nonthermal phase transitions that may occur after post-inflationary preheating in a simple model of a two-component scalar field with the effective potential $λ(φ_i^2 - {\rm v}^2)^2/4$, where $φ_1$ is identified with the inflaton field. We use three-dimensional lattice simulations to investigate the full nonlinear dynamics of the model. Fluctuations of the fields generated during and after preheating temporarily make the effective potential convex in the $φ_1$ direction. The subsequent nonthermal phase transition with symmetry breaking leads to formation of cosmic strings even for ${\rm v} \gg 10^{16}$ GeV. This mechanism of string formation, in a modulated (by the oscillating field $φ_{1}$) phase transition, is different from the usual Kibble mechanism.

Figures (7)

• Figure 1: Variances of the field components $\phi_2$ and $\phi_1$ (upper and lower solid curves respectively) as well as the zero modes of these fields (upper dotted curve is $\langle \phi_1\rangle$ and lower dotted curve is $\langle \phi_2\rangle$) are shown as functions of conformal time.
• Figure 2: Time dependence of the zero mode of $\phi_1$.
• Figure 3: Reconstruction of the effective potential in $\phi_{1}$ direction at several moments of time. Dots correspond to $\tau \approx 90$, diagonal crosses to $\tau \approx 110$, larger stars to $\tau \approx 180$ and smaller stars to $\tau \approx 215$. Solid line is the tree potential.
• Figure 4: The joint probability distribution function of $\phi_1$ and $\phi_2$ before and after the phase transition. Fields $\phi_1$ and $\phi_2$ are shown in units of ${\rm v}$.
• Figure 5: The process of string formation for ${\rm v} = 3\times 10^{16}$ GeV and $\lambda = 10^{-12}$.