Warped Self-Gravitating U(1) Gauge Cosmic Strings in 5D

TL;DR

This paper investigates warped five-dimensional cosmic string solutions, showing how brane-world models can address issues of string mass and observational constraints by warping the string tension down to acceptable levels.

Contribution

It introduces a new warped 5D cosmic string model where the four-dimensional spacetime is warped, avoiding conical deficits and observational issues associated with traditional cosmic strings.

Findings

Warped 5D cosmic strings can have their tension warped down to GUT scale.

The induced 4D spacetime lacks conical behavior and angle deficit.

Numerical solutions support the theoretical model.

Abstract

We present the "classical" Nielsen-Olesen vortex solution on a warped five dimensional space time, where we solved the effective four-dimensional equations from the five-dimensional equations together with the junction and boundary conditions. Four dimensional cosmic strings show some serious problems concerning the mechanism of string smoothing related to the string mass per unit length, $G\mu \leq 10^{-6}$. Moreover, there is no observational evidence of axially symmetric lensing effect caused by cosmic strings. Also super-massive cosmic strings ($G\mu\gtrsim 1$), predicted by superstring theory, possess some problems. They are studied because the universe may have undergone phase transitions at scales much higher than the GUT scale. But $G\mu \gtrsim 1$ is far above observational bounds, so one needs an inflationary scenario to smooth them out. Further, it is believed that these super-massive strings could never have extended to macroscopic size. Brane-world models could overcome these problems. $G\mu$ could be warped down to GUT scale, even if its value was at the Planck scale. In our warped cosmic string model, where the string mass per unit length in the bulk can be of order of the Planck scale, we find that the four dimensional brane space time is exponential warped down. Moreover, asymptotically the induced four dimensional space time doesn't show conical behavior. So there is no angle deficit compared to its value in the bulk and the space time seems to be un-physical, at least under fairly weak assumptions on the stress-energy tensor and without a positive brane tension. The results are confirmed by numerical solutions of the field equations.