Global texture as the origin of cosmic structure

If a unified theory possesses non-Abelian global symmetries which are spontaneously broken it gives rise to a three-dimensional defect known as texture. In an expanding universe texture obeys a ‘‘scaling solution,’’ which produces a constant density perturbation at horizon crossing of δρ/ρ≊$m_{\mathrm{GUT}{}^2/m_{\mathrm{Planck}{}^2}}$, where $m_{\mathrm{GUT}}$ is the scale of symmetry breaking. These (isocurvature) perturbations are broadly of Harrison-Zeldovich form, but are non-Gaussian, having strong ‘‘spikes’’ in the density field. Consequences for microwave background anisotropy are briefly discussed.