The power spectra of CMB and density fluctuations seeded by local cosmic strings

Abstract

We compute the power spectra in the cosmic microwave background and cold dark matter (CDM) fluctuations seeded by strings, using the largest string simulations performed so far to evaluate the two-point functions of their stress energy tensor. We find that local strings differ from global defects in that the scalar components of the stress-energy tensor dominate over vector and tensor components. This result has far reaching consequences. We find that cosmic strings exhibit a single Doppler peak of acceptable height at high $\ell$. They also seem to have a less severe bias problem than global defects, although the CDM power spectrum in the ``standard'' cosmology (flat geometry, zero cosmological constant, 5% baryonic component) is the wrong shape to fit large scale structure data.

Figures (2)

• Figure 1: The CMB power spectra predicted by cosmic strings decaying into loop and radiation fluids with $w^X=1/3, 0.1, 0.01, 0$. We have plotted $(\ell(\ell+1)C_\ell/2\pi)^{1/2}$ in $\mu K$, and superposed several experimental points. The higher curve corresponding to $w^X=1/3$ shows what happens if 5% of the energy goes into the radiation fluid.
• Figure 2: The power spectrum in CDM fluctuations for cosmic strings, with $w^X=0.01,0.1,1/3$. We plotted also the standard CDM scenario prediction and points inferred by Peacock and Dodds from galaxy surveys. The top 2 $w^X=1/3$ curves correspond to a 5% transfer into CDM, and a 20% transfer into baryons (top).