Cosmic String constraints from WMAP and the South Pole Telescope

TL;DR

This paper uses WMAP and South Pole Telescope data to place stringent limits on cosmic string contributions to CMB anisotropy, constraining string tension and guiding future detection efforts.

Contribution

It provides the first strong upper limits on cosmic string tension using combined WMAP and SPT data, refining constraints on string models.

Findings

String contribution to CMB anisotropy <1.75% (95% CL)

String tension Gμ < 1.7×10^{-7}

Future detection likely via B-mode polarization at small scales

Abstract

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.