NEW LOOK AT SUPERMASSIVE COSMIC STRINGS

Although it is well known that cosmic strings produced at grand-unified-theory (GUT) scales give rise to a conical spacetime, this picture must be revised for strings produced at much larger energy scales. An expression for the metric due to a supermassive cosmic string has recently been given by Laguna and Garfinkle. Here, we argue that their metric is not unique, and that a second solution exists which has different asymptotics. The existence of this new solution is verified numerically. Like the Laguna and Garfinkle metric, the solution we give is singular at finite distance from the core of the string. We further demonstrate that supermassive cosmic strings may also arise from symmetry breaking at GUT scales if the coupling between scalar and gauge fields is very weak. We argue that these low-energy supermassive strings are closely related to U(1) global strings, a result which is not surprising given their singular nature. By analogy with global strings, it is clear that the singularity of a low-energy supermassive string occurs at extremely large distances from the core of the string.