Fitting CMB data with cosmic strings and inflation

Abstract

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, we find a 2-sigma detection of strings: f_10 = 0.11 +/- 0.05, where f_10 is the fractional contribution made by strings in the temperature power spectrum (at multipole l = 10). CMB data give moderate preference to the model n = 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 and these extra data, we find that f_10 < 0.11, which corresponds to G mu < 0.7x10^-6 (where mu is the string tension and G is the gravitational constant).

Figures (2)

• Figure 1: The temperature power spectrum contribution from cosmic strings, normalized to match the WMAP data at $\ell=10$, as well as the best-fit cases from inflation only (model PL) and inflation plus strings (PL+S). These are compared to the WMAP and BOOMERANG data. The lower plot is a repeat but with the best-fit inflation case subtracted, highlighting the deviations between the predictions and the data. Note that the string contribution is identical to that shown in Fig. 14 of Bevis:2006mj, but here has a linear horizontal axis for $\ell>100$.
• Figure 2: The 2D marginalized likelihood distributions from CMB data (only) for $f_{10}$ versus $h$, $\Omega_{\mathrm{b}}h^{2}$, $A_{\mathrm{s}}^{2}$ and $n_{\mathrm{s}}$. Contours show the $68$ and $95\%$ confidence regions for model PL+S while the 400 MCMC points indicate the prefered region for HZ+S. The vertical lines on the $h$ and $\Omega_{\mathrm{b}}h^{2}$ plots show the $68$ and $95\%$ confidence limits from the HKP and BBN measurements.