The projected three-point correlation function:: Theory and observations

We report results for the angular three-point galaxy correlation function in the APM Galaxy Survey and compare them with theoretical expectations. For the first time, these measurements extend to sufficiently large scales to probe the weakly nonlinear regime. On large scales, the results are in good agreement with the predictions of nonlinear cosmological perturbation theory for a model with initially Gaussian fluctuations and linear power spectrum P(k) consistent with that inferred from the APM survey. These results reinforce the conclusion that large-scale structure is driven by nonlinear gravitational instability and that APM galaxies are relatively unbiased tracers of the mass on large scales; they also provide stringent constraints upon models with non-Gaussian initial conditions and strongly exclude the standard cold dark matter model.