The Doppler Peaks from Cosmic Texture

We compute the angular power spectrum of temperature anisotropies on the microwave sky in the cosmic texture theory, with standard recombination assumed. The spectrum shows`Doppler' peaks analogous to those in scenarios based on primordial adiabatic uctuations such as`standard CDM', but at quite diierent angular scales. There appear to be excellent prospects for using this as a discriminant between innationary and cosmic defect theories. The cosmic microwave background (CMB) anisotropy is the cleanest probe we have of structure formation in the universe, providing our best hope for deenitively connrming or excluding theories of the origin of structure. The COBE observation 1] provided the rst solid evidence of anisotropy, but due to its limited angular resolution it provided little more than an overall normalisation and rough evidence of scale invariance. Higher resolution experiments ooer the far richer prospect of a detailed measurement of the angular power spectrum and statistical properties of the anisotropies, which will give very powerful constraints on theories. Existing theories of the origin of structure fall into two categories, based upon either the ampliication of quantum uctuations in a scalar eld during innation or upon the process 1