Cosmic String constraints from WMAP and the South Pole Telescope
  The predictions of the inflationary LCDM paradigm match today's
high-precision measurements of the cosmic microwave background anisotropy
extremely well. The same data put tight limits on other sources of anisotropy.
Cosmic strings are a particularly interesting alternate source to constrain.
Strings are topological defects, remnants of inflationary-era physics that
persist after the big bang. They are formed in a variety of models of
inflation, including string theory models such as brane inflation. We assume a
"Nambu-Goto" model for strings, approximated by a collection of unconnected
segments with zero width, and show that measurements of temperature anisotropy
by the South Pole Telescope break a parameter degeneracy in the WMAP data,
permitting us to place a strong upper limit on the possible string contribution
to the CMB anisotropy: the power sourced by zero-width strings must be <1.75%
(95% CL) of the total or the string tension Gmu <1.7x10^{-7}. These limits
imply that the best hope for detecting strings in the CMB will come from B-mode
polarization measurements at arcminute scales rather than the degree scale
measurements pursued for gravitational wave detection.
