We perform a multiparameter likelihood analysis to compare measurements of the cosmic microwave background ( CMB ) power spectra with predictions from models involving cosmic strings .
Adding strings to the standard case of a primordial spectrum with power-law tilt n _ { \mathrm { s } } , we find a 2 \sigma detection of strings : f _ { 10 } = 0.11 \pm 0.05 , where f10 is the fractional contribution made by strings in the temperature power spectrum ( at \ell = 10 ) .
CMB data give moderate preference to the model n _ { \mathrm { s } } = 1 with cosmic strings over the standard zero-strings model with variable tilt .
When additional non-CMB data are incorporated , the two models become on a par .
With variable n _ { \mathrm { s } } and these extra data , we find that f _ { 10 } < 0.11 , which corresponds to G \mu < 0.7 \times 10 ^ { -6 } ( where \mu is the string tension and G is the gravitational constant ) .