Musings

Cosmic Strings

I’ve blogged a bit about the resurgence of interest in cosmic strings, in the context of string theory. In the old days, it was hard to imagine that cosmic (fundamental) strings would have tensions much below the GUT scale. Recent understandings of compactifications with fluxes lead very naturally to strings with tensions much below the GUT scale. That’s exciting because such beasts might actually be observable (but, hopefully, not ruled out by existing CMB data).

Tom Kibble has a very nice review on cosmic strings, the current observational limits, and some intriguing observations of what may be gravitational lensing by an oscillating cosmic string, as well as some other candidates for cosmic string lensing. The string tension would seem to be about $G\mu \sim \text{few}\times 10^{-7}$, which would be consistent with bounds from WMAP:

where $\lambda$ is the intercommutation probability, $\lambda\lt 1$, and $B$ is the fraction of the CMB power spectrum due to cosmic strings, which certainly satisfies $B\lt 0.1$. There are some more stringent bounds that have been argued for recently, but Kibble does not seem to put much stock in them.