Large-scale structure, the cosmic microwave background and primordial non-Gaussianity

Cosmic microwave background and large-scale structure data will shortly imp rove dramatically with the Microwave Anisotropy Probe and Planck Surveyor, and the Anglo-Australian 2-Degree Field and Sloan Digital Sky Survey. It is therefore timely to ask which of the microwave background and large-scale structure will provide a better probe of primordial non-Gaussianity. In thi s paper we consider this question, using the bispectrum as a discriminating statistic. We consider several non-Gaussian models and find that in each c ase the microwave background will provide a better probe of primordial non- Gaussianity. Our results suggest that if microwave background maps appear G aussian, then apparent deviations from Gaussian initial conditions in galax y surveys can be attributed with confidence to the effects of biasing. We d emonstrate this precisely for the spatial bispectrum induced by local non-l inear biasing.