Planck2013 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 line-of-sight Boltzmann solvers. We have studied Nambu-Goto 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 = 10. This parameter has been added to the standard six parameter fit using COSMOMC with flat priors. For the Nambu-Goto 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 high-CMB data. For the Abelian-Higgs 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 non-Gaussian signatures of cosmic strings, calibrating with all-sky Planck resolution CMB maps generated from networks of post-recombination strings. We have validated our non-Gaussian searches using these simulated maps in a Planck-realistic context, estimating sensitivities of up to ∆Gµ/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 post-recombination string contributions have been included in the non-Gaussian analysis.

Constraining topological defects with temperature and polarization anisotropies

“…The relative proportions of scalar, vector and tensor perturbations are essentially fixed for a given type of defect, so a constraint on one of the modes will imply constraints on the others. It is worth noting that even though defects are highly constrained via the CMB temperature anisotropies [16][17][18][19][20][21][22], they can still contribute importantly to the B-mode polarization.…”

Observational Constraints on Cosmological Superstrings

“…In addition, it is less hope to observe so-called "light" strings (with energies less than 10 15 GeV) in CMB data, [8].…”

“…Hybrid cosmic string models become of particular interest because they are preferred both in terms of simulations [9], and from the point of view of the observational data on the CMB anisotropy (the most high upper limit from the analysis of the CMB angular spectra, [8], and from the search of individual strings, [15]). Interest in the cosmic strings is manifested by the superstring physics as such objects may be the only observational evidence for superstring models [23].…”

“…These exotic structures are predicted by theory, but have not been found yet. The strings can be responsable for no more than 4.4% of the CMB anisotropy signal (at multipole l = 10), [8].…”

“…therein) and search for cumulative restriction for string angular power spectrum in CMB data, [8]; -Direct search for individual strings through step-like temperature discontinuity, [14] (statement of Canny algorithm for future CMB experiments), [15] (method based on Haar convolution, i.e. MHF method), where the search for temperature gradients in CMB maps is discussed.…”