Canny Algorithm, Cosmic Strings and the Cosmic Microwave Background

Abstract

We describe a new code to search for signatures of cosmic strings in cosmic microwave anisotropy maps. The code implements the Canny Algorithm, an edge detection algorithm designed to search for the lines of large gradients in maps. Such a gradient signature which is coherent in position space is produced by cosmic strings via the Kaiser-Stebbins effect. We test the power of our new code to set limits on the tension of the cosmic strings by analyzing simulated data with and without cosmic strings. We compare maps with a pure Gaussian scale-invariant power spectrum with maps which have a contribution of a distribution of cosmic strings obeying a scaling solution. The maps have angular scale and angular resolution comparable to what current and future ground-based smallscale cosmic microwave anisotropy experiments will achieve. We present tests of the codes, indicate the limits on the string tension which could be set with the current code, and describe various ways to refine the analysis. Our results indicate that when applied to the data of ongoing cosmic microwave experiments such as the South Pole Telescope project, the sensitivity of our method to the presence of cosmic strings will be more than an order of magnitude better than the limits from existing analyses.

Disruption of cosmic string wakes by Gaussian fluctuations

“…At this point, we will switch from natural units to units used conventionally in cosmology, namely Mpc for lengths and seconds for time. In these units c = 9.6 × 10 −15 Mpc/s, and the expression on the right hand side of (19) has to be multiplied by c n+3 . We will also use vγ(v) = c/ √ 3, z i = 1000 and t 0 = 4.35 × 10 17 s The transfer function T from ( [27] page 60) is used to obtain an analytic expression for ∆(k 3 ), which together with the approximation (k 3 (z)) −0.0145 ≈ 1 gives…”

“…The cosmic string signals are also most easily visible in position space maps (e.g. with edge detection algorithms [19]), whereas the distincitve stringy features are washed out in power spectra (see e.g. [20]).…”

Wavelet-Bayesian inference of cosmic strings embedded in the cosmic microwave background

“…Various methods have been developed to search for stringinduced contributions to the CMB, from power-spectrum constraints (Lizarraga et al 2014a(Lizarraga et al ,b, 2016Charnock et al 2016), to higher-order statistics such as the bispectrum (Planck Collaboration XXV 2014; Regan & Hindmarsh 2015) and trispectrum (Fergusson et al 2010), and tools such as edge detection (Lo & Wright 2005;Amsel et al 2008;Stewart & Brandenberger 2009;Danos & Brandenberger 2010), Minkowski functionals (Gott et al 1990;Ducout et al 2013;Planck Collaboration XXV 2014), wavelets and curvelets (Starck et al 2004;Hammond et al 2009;Wiaux et al 2010;Planck Collaboration XXV 2014;Hergt et al 2016), level crossings (Sadegh Movahed & Khosravi 2011), and peakpeak correlations (Movahed et al 2013). Current constraints on the string tension depend on the string model and simulation technique adopted.…”

Observational Constraints on Cosmological Superstrings

“…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.…”