Y-junction intercommutations of current carrying strings

Abstract

Under certain conditions the collision and intercommutation of two cosmic strings can result in the formation of a third string, with the three strings then remaining connected at Y-junctions. The kinematics and dynamics of collisions of this type have been the subject of analytical and numerical analyses in the special case in which the strings are Nambu-Goto. Cosmic strings, however, may well carry currents, in which case their dynamics is not given by the Nambu-Goto action. Our aim is to extend the kinematic analysis to more general kinds of string model. We focus in particular on the collision of strings described by conservative elastic string models, characteristic of current carrying strings, and which are expected to form in a cosmological context. As opposed to NambuGoto strings collisions, we show that in this case the collision cannot lead to the formation of a third elastic string: if dynamically such a string forms then the joining string must be described by a more general equation of state. This process will be studied numerically in a forthcoming publication.

Revisiting Y junctions for strings with currents: Transonic elastic case

“…We re-examine the exact solution for these strings [44,47], obtain left-/right-moving modes, and in line with [20] we derive kinematic conditions under which the production of Y-junction is possible. The result obtained in this paper is in conflict with conclusion of the work [48]. The explanation of this situation is given in the end of section V.…”

“…The problem of Y-junctions for Nambu-Goto current carrying strings was initially studied in [48]. The authors developed covariant formalism to investigate under which conditions the production of Y-junctions is possible.…”

Collisions of cosmic strings with chiral currents

“…It is important to specify the difference between chiral strings, considered in this paper, and electric/magnetic strings studied in [40]. Due to the chiral conditions (Eq.…”

“…If these additional multipliers D and values of currents F 2 are not fixed separately (since they appear in equation of state only as a combination F 2 D), they allow enough freedom to avoid the overdetermination issue for the case of the chiral current. This approach is specific to the chiral type of current and won't change the previously obtained result for magnetic and electric cases [40].…”

“…We anticipate that Y junction production can also arise more generally for strings with non-trivial structure. A comprehensive study of such a situation was presented in [40]. Specifically, the authors of [40] considered collisions of strings with electric current (time-like state parameter κ < 0 -see Section II below for a more precise definition of κ) and magnetic current (space-like state parameter κ > 0).…”