Collisions of Cosmic F- and D-strings

Abstract

Recent work suggests that fundamental and Dirichlet strings, and their (p,q) bound states, may be observed as cosmic strings. The evolution of cosmic string networks, and therefore their observational signals, depends on what happens when two strings collide. We study this in string perturbation theory for collisions between all possible pairs of strings; different cases involve sphere, disk, and annulus amplitudes. The result also depends on the details of compactification; the dependence on ratios of scales is only logarithmic, but this is still numerically important. We study a range of models and parameters, and find that in most cases these strings can be distinguished from cosmic strings that arise as gauge theory solitons.

Figures (7)

• Figure 1: When two strings of the same type cross, they can reconnect (intercommute).
• Figure 2: Possible reconnections of $(p_1,q_1)$ and $(p_2,q_2)$ strings; $i$ stands for $(p_i,q_i)$.
• Figure 3: F--F reconnection with strings wound on a torus. This is a closed+closed$\,\to\,$closed transition.
• Figure 4: F--D reconnection with strings wound on a torus. This is a closed$\,\to\,$open transition.
• Figure 5: D-strings after a collision that produces open F-string pairs. The upper D-string is rotated by an angle $\theta$ relative to the lower, around the axis defined by the F-strings. The angle $\phi'$ is the angle $\phi$ introduced in the text, boosted by the velocity of the vertex.