Planck 2013 results. XXV. Searches for cosmic strings and other topological defects
Abstract
Planck data have been used to provide stringent new constraints on cosmic strings and other defects. We describe forecasts of the CMB power spectrum induced by cosmic strings, calculating these from network models and simulations using lineofsight Boltzmann solvers. We have studied NambuGoto cosmic strings, as well as field theory strings for which radiative effects are important, thus spanning the range of theoretical uncertainty in the underlying strings models. We have added the angular power spectrum from strings to that for a simple adiabatic model, with the extra fraction defined as f_{10} at multipole ℓ = 10. This parameter has been added to the standard six parameter fit using COSMOMC with flat priors. For the NambuGoto string model, we have obtained a constraint on the string tension of Gμ/c^{2} < 1.5 × 10^{7} and f_{10} < 0.015 at 95% confidence that can be improved to Gμ/c^{2} < 1.3 × 10^{7} and f_{10} < 0.010 on inclusion of highℓ CMB data. For the AbelianHiggs field theory model we find, Gμ_{AH}/c^{2}< 3.2 × 10^{7} and f_{10} < 0.028. The marginalised likelihoods for f_{10} and in the f_{10}Ω_{b}h^{2} plane are also presented. We have additionally obtained comparable constraints on f_{10} for models with semilocal strings and global textures. In terms of the effective defect energy scale these are somewhat weaker at Gμ/c^{2} < 1.1 × 10^{6}. We have made complementarity searches for the specific nonGaussian signatures of cosmic strings, calibrating with allsky Planck resolution CMB maps generated from networks of postrecombination strings. We have validated our nonGaussian searches using these simulated maps in a Planckrealistic context, estimating sensitivities of up to ΔGμ/c^{2} ≈ 4 × 10^{7}. We have obtained upper limits on the string tension at 95% confidence of Gμ/c^{2} < 9.0 × 10^{7} with modal bispectrum estimation and Gμ/c^{2} < 7.8 × 10^{7} for real space searches with Minkowski functionals. These are conservative upper bounds because only postrecombination string contributions have been included in the nonGaussian analysis.
 Publication:

Astronomy and Astrophysics
 Pub Date:
 November 2014
 DOI:
 10.1051/00046361/201321621
 arXiv:
 arXiv:1303.5085
 Bibcode:
 2014A&A...571A..25P
 Keywords:

 cosmic background radiation;
 cosmological parameters;
 early Universe;
 largescale structure of Universe;
 cosmology: theory;
 cosmology: observations;
 Astrophysics  Cosmology and Nongalactic Astrophysics
 EPrint:
 20 pages, 15 figures